|| The following document is scanned from Professional Paper 901, which is
out of print and no longer available in printed form. The entire book is
present. The original book was typeset in two columns. The screen
displays the columns sequentially, one column at a time. Each page number
precedes the text on that page. No page breaks have been inserted. Long
lines such as captions would have required scrolling to read, and they were
broken into shorter lines. Codes for the figure and table numbers are in
the Contents, text, and captions; the BROWSE program allows the user to
view the figures and table 1 by selecting the codes, which are in square
brackets and look like this: [FIG_1].
EXPLANATORY TEXT TO ACCOMPANY THE
GEOLOGIC MAP OF THE UNITED STATES
By Philip B. King and Helen M. Beikman
Geological Survey Professional Paper 901
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON:1974
UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
V. E. McKelvey, Director
Library of Congress catalog - card No. 74-600169
For Sale by the Superintendent of Documents, U.S. Government Printing
Office Washington, D.C. 20402 - Price $1.25 (paper cover)
Stock Number 2401-02573
Introduction ------------------------------------------ 1
Previous geologic maps of the United States------------- 1
Sources of information ------------------------------- 1
Maps published before 1860 -------------------------- 1
Maps between 1860 and 1880 ------------------------- 7
Maps between 1880 and 1930 ------------------------- 7
The Geologic Map of the United States of 1932 ------ 9
The Geologic Map of the United States ----------------- 10
History of the present project----------------------- 10
Sources of the Geologic Map ------------------------- 11
Uses of the Geologic Map --------------------------- 18
Methods of compilation ----------------------------- 18
Contents of the Geologic Map ------------------------ 20
Classification of the rock units -------------------- 21
Symbolization of rock units ------------------------ 25
Representation of faults ---------------------------- 28
Representation of contacts -------------------------- 31
Subcrop geology ------------------------------------- 31
Northern Interior States -------------------------- 31
Eolian deposits ---------------------------------- 35
Atlantic Coastal Plain----------------------------- 36
Radiating strikes------------------------------------ 36
References cited--------------------------------------- 38
FIGURE 1 [FIG_1]. Geology of the United States as represented by Maclure
(1817) ---------------------------------------------------- 1
2 [FIG_2]. Geology of the United States and adjacent parts of Canada
as represented by Lyell (1845) --------------------------- 4
3 [FIG_3]. Geology of the United States and adjacent parts of Canada
as represented by Marcou (1855) -------------------------- 5
4 [FIG_4]. Geology of the United States and adjacent parts of Canada
as represented by Edward Hitchcock (1854) ----------------- 6
5 [FIG_5]. Index map showing areas represented geologically on McGee
map of 1885, areas added or revised on the McGee map of 1894,
and additional coverage based on less exact information on the
C. H. Hitchcock map of 1887 -------------------------------- 8
6 [FIG_6]. Index map of Texas, showing areas covered by different
sources used on the Geologic Map -------------------------- 17
7 [FIG_7]. Index map of the United States, showing areas covered by
the different sources used for the subsea contours on the
Geologic Map ---------------------------------------------- 19
8 [FIG_8ab][FIG_8c]. Geologic maps of the Sandia Mountains,
New Mexico, to illustrate the process of generalizing data
for the Geologic Map of the United States ----------------- 22
9 [FIG_9]. Map of the Great Basin in Nevada and Utah, showing
regional extent of major low-angle thrust faults that are
represented on the Geologic Map of the United States as
exposed fragments in the mountain areas ------------------- 29
1O [FIG_10]. Circular faults shown on the Geologic Map of the United
11 [FIG_11]. Maps of eastern South Dakota, to illustrate problems of
representing bedrock geology in areas with extensive cover of
surficial deposits ---------------------------------------- 32
12 [FIG_12]. Generalized geologic map of eastern Middle Western
States, to show relations of subcrop geology to preglacial
river systems --------------------------------------------- 33
13 [FIG_13]. Geologic map of northern Minnesota, showing the extent
of thin Upper Cretaceous deposits (Coleraine Formation) that
are not represented on the Geologic Map of the United
States ---------------------------------------------------- 34
14 [FIG_14]. Map of western Nebraska, showing bedrock geology as
represented on the Geologic Map of the United States,
superposed on which are the areas of Quaternary sand dunes and
drifted sand (Sand Hills Formation) as represented on the
Geologic Map of the United States of 1932 and by Thorp and
Smith (1952) ---------------------------------------------- 35
15 [FIG_15]. Geologic map of the Atlantic Coastal Plain in Maryland,
Delaware, and New Jersey, showing the relation of the bedrock
units that appear on the Geologic Map of the United States to
surficial deposits of Quaternary and late Tertiary age ---- 37
16 [FIG_16]. Map of the southern Midcontinent region in Oklahoma,
Arkansas, and Texas, showing "radiating strikes" in Paleozoic
and Cretaceous rocks -------------------------------------- 38
[TABLE_1]. Comparison between "American" and "International" systems
of coloring stratified rocks on maps ---------------------- 27
EXPLANATORY TEXT TO ACCOMPANY THE
GEOLOGIC MAP OF THE UNITED STATES
By Philip B. King and Helen M. Beikman
The U.S. Geological Survey has published a new
Geologic Map of the United States (exclusive of Alaska
and Hawaii) on a scale of 1:2,500,000, which was com-
piled between 1967 and 1971 by Philip B. King and
Helen M. Beikman, with geologic cartography by Ger-
trude J. Edmonston. The map replaces the now outdated
Geologic Map of the United States on the same scale,
which was compiled by George W. Stose and Olof A.
Ljungstedt and was issued by the U.S. Geological Sur-
vey in l932.
This report is intended to supplement the new map
and to provide background information to assist its user
in interpreting it. It describes the historical antecedents
of the map and the sources from which the map was
compiled and discusses various general topics related to
it. Succeeding reports will amplify the necessarily brief
descriptions of the map units which appear in its legend
and will deal at length with specific geological problems
in the United States, insofar as they relate to represen-
tation of the features in map form.
PREVIOUS GEOLOGIC MAPS OF
THE UNITED STATES
SOURCES OF INFORMATION
Source data for previous geologic maps of the Un-
ited States are plentiful, so we have chosen here to
present a narrative account, describing the circum-
stances under which the maps were prepared and com-
menting on their more interesting features, rather than
list details which the reader can find in the published
sources. Maps that appeared before the mid-188O's have
been listed and annotated by Marcou and Marcou (1884,
p. 23-32) and have been described at length by C. H.
Hitchcock (1887); Jillson (1950) has extended the list-
ing to 1946. In our account we have ignored many maps
that appear in these published lists as being merely
reprints in the same or slightly different form by a
single author, or copies of such maps in textbooks and
other media. Much information on the circumstances of
geologic maps published by the U.S. Geological Survey
can be found in the Annual Reports of the Survey. In-
teresting contemporary reviews of some of the maps are
cited in "Geologic literature on North America,
1785-1918" (Nickles, 1923). For our narrative, we have
obtained background information from Merrill's "Con-
tributions to the history of American Geology" down to
1880 (1906), and from biographies of later geologists,
such as the Memorials of the Geological Society of
America, Darrah's "Powell of the Colorado" (1951),
Stegner's "Beyond the Hundredth Meridian" (1954),
and Willis's autobiographical "A Yanqui in Patagonia"
(1947, especially p. 30-35). Copies of most of the maps
referred to here are in the files of the Library of the U.S.
Geological Survey, and we are indebted to Mark Pang-
born, curator of these maps, for his generous assist-
MAPS PUBLISHED BEFORE 1860
Efforts to portray on a map the geology of what is now
the United States extend back more than two centuries.
The first recorded attempt is a "Mineralogic map, show-
ing the nature of the terrains of Canada and Louisiana"
("Carte minralogique o l'on voit la nature des ter-
rains du Canada et de la Louisiane"), by the French
geologist Jean tienne Guettard, published in 1752, at
a time when a large part of the region was still French
territory. Whether he visited North America is not cer-
tain, and most of his information was compiled from
reports of French officers. A belt of marl and clay is
shown extending from the Gulf of Mexico to Cape Bre-
ton Island, and thence inland toward Quebec. Between
it and the coast is a sandy belt, and west of it a schistose
and metalliferous belt. Different signs and annotations
indicate the places where rocks and minerals were re-
ported between the Atlantic Coast and the Rocky Moun-
Aside from this primitive effort, the first geologic map
of the United States is that published by William Mac-
lure in 1809, of which a revised version appeared in
1817 [FIG_1]. Maclure was a Scotsman who came to
America as a merchant and after his retirement became
interested in the sciences; for 22 years he was president
of the Philadelphia Academy of Natural Sciences. To
Figure 1 [FIG_1].--Geology of the United States as represented by Maclure
(1817). Original map in color. Note: To facilitate comparison of figures 1
through 4, the original geological representations have been replotted on
the same projection and base. State and national boundaries are retained as
they existed at the times of publication; in figures 3 and 4 the geography
west of the Mississippi River and within the coastlines is retained as on
assemble his map, he traveled widely through what was
then the United States, and especially the part east of
the Mississippi River. Both editions of his map were
accompanied by an explanatory text, including "re-
marks on the effect produced on the nature and fertility
of the soils by the decomposition of the different classes
In accord with the prevailing thinking of his day,
Maclure classified the rocks on Wernerian principles,
dividing them into Primitive, Transition, Secondary or
Floetz (including a unit of Old Red Sandstone), and
Alluvial. On the map of 1817, a line is marked along the
Appalachians "to the westward of which is found the
greatest part of the Salt and Gypsum." In modern terms,
his "Primitive Rock" corresponds to the Precambrian
and other crystalline rocks of the Adirondack Moun-
tains, New England, and the Piedmont Province; his
"Transitional Rock" to the folded Paleozoic of the Ap-
palachians; his "Secondary Rock" to the flat-lying
Paleozoic farther west; his "Old Red Sandstone" to the
Triassic Newark Group; and his "Alluvial Rock" to the
Cretaceous and Tertiary deposits of the Coastal Plain.
No significant geologic maps of the whole United
States appeared for many years after Maclure's publica-
tion, but important maps of parts of the region were
made. The most notable was that by James Hall which
accompanied his classic Part 4 of "Geology of New York"
(1843), dealing with the western part of the State and
establishing the fundamentals of Paleozoic stratig-
raphy in a large part of the country. The map includes
not only Hall's survey in New York but also his recon-
naissance observations farther west and represents in
fair detail the Northern States as far south as Virginia
and as far west as the Mississippi River on a scale of
1:1,850,000. In addition, geology was also sketched on
maps showing the routes of some of the exploring exped-
itions, such as that of Major S. H. Long's expedition to
the Rocky Mountains (James, 1823), and David Dale
Owen's to the northern Middle Western States (1843).
In 1845, Sir Charles Lyell published an account of his
epochal travels in North America in 1841 and 1842,
which was accompanied by a "Geological Map of the
United States, Canada, etc., compiled from the State
Surveys of the U.S. and other sources" on a scale of
1:7,620,000 [FIG_2]. (The sources of the map are de-
scribed at length at the end of the book: v. 2, p. 198-219.)
Wernerian concepts had by now disappeared, and the
rocks were divided into conventional systems and series
(Hypogene, Potsdam, Lower Silurian, Upper Silurian,
Devonian, Coal Measures, New Red Sandstone, Cre-
taceous, Eocene, Miocene, and others). These are shown
in much detail westward as far as the Mississippi River,
and more vaguely for several hundred miles farther
west. The map illustrates vividly the improvements
that had been made in representation since the last
Maclure map of 1817, as a result of geological mapping
in the United States during the intervening 28 years.
Between 1845 and 1853 the territory of the United
States was extended northward, southward, and west-
ward to its present conterminous limits by various ac-
quisitions, which greatly expanded the field for geologi-
cal exploration and mapping and also enlarged the
problem of making a geological map of the United
Between 1853 and 1858, Jules Marcou produced a
succession of geological maps of the United States, the
later ones extending to the Pacific Coast [FIG_3]. Marcou
was a Frenchman, who came to this country as a protege
of Louis Agassiz and became a controversial figure. His
representation of the western country was based in part
on his service with some of the exploring expeditions for
the Pacific Railroad, but to an even greater extent on
freehanded extrapolation and speculation. His maps
received harsh reviews from his none-too-friendly
American colleagues (Hall, 1854; Blake, 1856), one of
whom stated that "there is here a disregard of published
results and an audacious attempt at generalization that
has seldom been equalled." Viewed from a distance of
more than a century, one can deplore Marcou's failure to
use available data yet commend his bold attempt to
present the general geological aspect of the western
country, which his contemporaries had been reluctant
James Hall, one of Marcou's critics, in collaboration
with J. P. Lesley, compiled a geological map of the
region west of the Mississippi for the report of the
United States and Mexican Boundary Survey (Hall and
Lesley, 1857), based not only on the results of the boun-
dary survey, but also on the Pacific Railroad surveys
and other expeditions. Their map represented only the
areas of outcrop that had been identified or reasonably
inferred and left the remaining areas uncolored. Thus,
no regional picture emerges, such as the one attempted
Less commendable than these was a contemporary
map of the United States by Edward Hitchcock, profes-
sor of geology at Amherst College, which accompanied
his "Outlines of the geology of the globe, and of the
United States in particular" (1854) [FIG_4]. This map
was made by combining Lyell's geologic map of the
eastern part of the country with the representation of
the western part from Bou's "Geological Map of the
World," with a few emendations--with such absurd re-
sults that the map would not deserve notice except for
the eminence of its author.
Figure 2 [FIG_2].--Geology of the United States and adjacent parts of
Canada as represented by Lyell (1845). Original map in color.
Figure 3 [FIG_3].--Geology of the United States and adjacent parts of
Canada as represented by Marcou (1855) Original map in color.
Figure 4 [FIG_4].--Geology of the United States and adjacent parts of
Canada as represented by Edward Hitchcock (1854). Original map in color.
MAPS BETWEEN 1860 AND 1880
After the Civil War period, notable improvements
were made in geological map publishing, as color
lithography replaced the former laborious method of
coloring printed geological maps by hand. Also, rep-
resentation of the western country passed from the
realms of fantasy to fact as a result of mapping by the
Territorial Surveys and other official organizations.
A noteworthy product of this period is the geologic
map (scale 1:1,584,000) that accompanied Sir William
Logan's report on "The Geology of Canada" (Logan and
others, 1863; the map is dated 1866, but was not issued
until 1869). It included not only Canadian territory, but
also the part of the United States north of the fortieth
parallel and east of the ninety-sixth meridian, based on
data supplied by James Hall (see footnote 1).
Footnote 1. This map is highly praised by C. H. Hitchcock (1887, p. 478-
481), who notes that it was omitted from the listing by Marcou and Marcou
(1884), and comments that this "must be compared to the celebrated
performance of Hamlet where, owing to infelicitous circumstances, the part
of Hamlet was omitted!"
As a result of the new surveys assembling a reasona-
bly expressive geologic map of the whole country be-
came possible. Compilation of such a map on a scale of
1:7,000,000 was made by Charles H. Hitchcock and
William P. Blake and appeared in various official re-
ports, notably in the "Statistical Atlas of the United
States" that accompanied the report of the Ninth Cen-
sus of 1870 (1874), a volume which also contains an
explanation by the compilers of their sources and
methods. Hitchcock was the son of Edward Hitchcock
and was himself an eminent New England geologist;
Blake had had long experience in western exploration
and was at the time professor at California College (the
predecessor of the University of California). Aside from
the many virtues of the map, one can note adversely
that they assigned the granites and other plutonic rocks
in the Sierra Nevada and eastward into the Great Basin
to the "Archean"; this echoed the conclusion of the
geologists of the Fortieth Parallel Survey and many
contemporaries, even though a reviewer (Anonymous,
1873) had requested that those in the Sierra Nevada be
transferred to the Triassic and Jurassic. More curious is
the complete omission of the Idaho batholith, or broad
granitic terrane, of central Idaho; its area is represented
as being geologically like the Great Basin, consisting of
half a dozen strips of Cambrian and Archean rocks,
separated by strips of Cenozoic.
Hitchcock himself also published privately a geologic
wall map of the United States (1881) on a scale of
1:1,226,200, measuring 13 feet long and 8 feet high--
the largest geologic map of the whole country that has
ever been issued. Although the geographic base of this
map is much more detailed that that of the smaller
geologic maps by Hitchcock and Blake, the geologic
representation shows no greater refinement, nor indeed
was any possible from information available at the time
(compare Anonymous, 1881).
MAPS BETWEEN 1880 AND 1930
In 1882, 3 years after the U.S. Geological Survey was
organized, it was instructed by Congress "to complete a
geological map of the United States." This gave the
Survey authority to conduct geological investigations
in all parts of the country, and it also obligated the
Survey to prepare a national geologic map. In the
summer of 1883, Director J. W. Powell instructed W J
McGee to compile such a map in time for Congressional
hearings the following spring; the map was published in
the Fifth Annual Report of the Survey (McGee, 1885b)
on a scale of 1:7,115,000, with the title "Map of the
United States exhibiting the present status of know-
ledge relating to the areal distribution of the geological
groups." Although the published map states that it was
"compiled by W J McGee," he gives generous credit in
his administrative report to the assistance of C. H.
Hitchcock for his "experience and skill in geologic car-
tography, his extended personal knowledge of Ameri-
can terranes, and his familiarity with American geolog-
ical literature" (McGee, 1885a, p. 35).
On McGee's map the two-thirds of the country east of
the one hundred and third meridian is completely col-
ored, but in the western third only the areas mapped by
the various Territorial Surveys are colored, the re-
mainder being left blank [FIG_5]. As McGee explains
(1885a, p. 38),
Much of the western part of the United States remains unexplored
geologically; repeated efforts were made to gain access to the unpub-
lished material of the now suspended Geological Survey of California,
and to establish correspondence with the State Geologist of Oregon,
but without success; the maps prepared by the earliest western ex-
plorers can seldom be accurately coordinated with those recently pub-
lished, either geographically or geologically; and it became necessary
to leave the following States and Territories either partially or wholly
uncolored: Arizona, California, Idaho, Montana, Nevada, New Mex-
ico, Oregon, Texas, Utah, Washington.
On completion of this work for McGee, Hitchcock
obtained permission from Director Powell to fill in the
remaining western part of the map from less exact data,
and the results were published in the Transactions of
the American Institute of Mining Engineers (Hitch-
cock, 1887), with an explanatory text. His additions to
the Survey map closely resemble the representation on
the earlier maps by Hitchcock and Blake, but there are
changes and refinements.
In 1894 the U.S. Geological Survey published a re-
vised version of the official map, again with the author-
ship of McGee and on the same scale as before, entitled
"Reconnaissance map of the United States, showing the
distribution of the geologic systems so far as known."
Figure 5 [FIG_5].--Index map showing areas represented geologically on
McGee map of 1885, areas added or revised on the McGee map of 1894, and
additional coverage based on less exact information on the C. H. Hitchcock
map of 1887.
Important improvements were made in the previously
colored area east of the one hundred and third meridian,
especially in the Great Plains from Kansas to Texas,
and in the Appalachians. Parts of the area farther west
that had hitherto been left blank were filled in, espe-
cially in the Sierra Nevada and elsewhere in California,
but based on new mapping by U.S. Geological Survey
personnel, as the results of the Geological Survey of
California had never been obtained. Unfortunately, the
compilers of the revised map chose to group the volcanic
and plutonic rocks in the Sierra Nevada and elsewhere
in the west into a single "igneous" unit, thus ignoring
fundamental distinctions for which many data were
already available. Representation of the bedrock in the
northern tier of States and Territories was also obs-
cured by overprinting a pattern of glacial deposits.
When McGee transferred to the Bureau of American
Ethnology in 1894, responsibility for national geologic
maps devolved on Bailey Willis as Map Editor. In 1895
his staff was augmented by George W. Stose as geologist
and Olof A. Ljungstedt as cartographer. Shortly after-
wards, when Willis became Geological Assistant to Di-
rector C. D. Walcott, Stose became Map Editor;
nevertheless, Willis and Stose continued their collab-
oration for many years. Willis was part of a Survey
committee on a Geologic Map of the United States, and
plans were formulated for a new map which was to be on
a scale of 1:2,500,000. Stose assembled a manuscript
copy of such a map which formed part of the Survey
exhibit at the Louisiana Purchase Exposition in St.
Louis in 1904, but attempts to put it into more perma-
nent form were hindered because of lack of an adequate
geographic base and the need for more large-scale
geologic maps of the States to serve as source material.
Also, the impending Tenth International Geological
Congress to be held in Mexico in 1906 indicated the need
for a Geologic Map of North America, and Willis and his
assistants quickly produced a preliminary version of
this map on a scale of 1:5,000,000 with the cooperation
of the Governments of Canada and Mexico, which was
published by the Congress as "Carte Gologique de
l'Amrique du Nord" (Willis, 1906). It then appeared
more desirable to perfect this preliminary rendering of
North American geology than to continue on the pro-
posed Geologic Map of the United States. An improved
version of the Geologic Map of North America was vir-
tually completed by 1910 and published in 1911 under
the authorship of Willis and Stose; it was also included
as a companion to Willis' monumental "Index to the
Stratigraphy of North America" in Professional Paper
On the Geologic Map of North America of 1912 exten-
sive areas north and south of the United States could
not be adequately represented on account of lack of
geological knowledge, and some areas in Alaska, north-
ern Canada, and Central America were left uncolored.
However, the geology of the United States and southern
Canada were shown in much detail; the part in the
United States no doubt included the data thus far as-
sembled for the postponed Geologic Map of the United
States. For the succeeding 20 years the North America
map was the standard reference work for United States
geology--including King's student days between 1920
THE GEOLOGIC MAP OF THE UNITED STATES OF 1932
For a considerable period after Willis left the Survey,
Stose had to devote his efforts to the preparation or
editing of State Geologic Maps on larger scales, al-
though the eventual objective of a Geologic Map of the
United States was not forgotten. Actual compilation of
this map began in 1927 and was accelerated by the
decision of the Fifteenth International Geological Con-
gress held in South Africa in 1929 to hold its Sixteenth
Congress in the United States in 1933. Work proceeded
with sufficient rapidity that printed copies of the map
were distributed to participants of this Congress in the
summer of 1933 (but with a publication date of 1932).
Stose assumed primary responsibility for preparation
of the map. He compiled the Appalachian part, in which
he had long been interested, and supervised the compila-
tions of his associates; initial compilations of many
areas outside the Appalachians were made by O. A.
Ljungstedt, who was not a professional geologist but
who had had long experience as a geologic cartographer
in the Map Editor's office. Stose traveled widely to ob-
tain manuscript data, especially from State Maps that
were in process of compilation. Nevertheless, adequate
source maps were still lacking for much of the north-
western part of the country, so Stose and Ljungstedt,
with the aid of local specialists, made original compila-
tions of Nevada, Idaho, Oregon, and Washington on
scales of 1:1,000,000 or larger. In addition, Anna I.
Jonas (later Mrs. G. W. Stose) was added to the staff to
complete a reconnaissance of the Piedmont province
which she had already begun in connection with prep-
aration of a Geologic Map of Virginia.
The resulting map, attractively printed in many col-
ors, served as a reference work on the geology of the
United States for the succeeding forty years; it was
reprinted in 1960 when the stock of the original print-
ing was exhausted. The map represents the best sum-
mary that could be made in its time, not only of the areal
geology of the country, but also of the prevailing geolog-
ical philosophy. Any apparent imperfections that we
might now see in the map should be viewed in this
Many geologic features of the country were poorly
coordinated at the time; consequently greater emphasis
was given to rock-stratigraphic than to time-
stratigraphic units. The geology is treated in terms of
nine geological subdivisions or provinces, shown on an
index map, for each of which there is a separate legend.
The sequences in some of the provinces are very
different--for example, those in the Lake Superior re-
gion and the Coastal Plains--but others partly overlap
in age, and correspondence between these from one
legend to another is not always clear.
Some of the stratigraphic classifications have
changed since 1932, resulting in improvements in rep-
resentation not possible at the time. Thus, the "Car-
boniferous System" is now divided into the Mississip-
pian, Pennsylvanian, and Permian Systems, creating
changes in letter symbols, coloring, and even to some
extent in geological concepts. Also, separation of the
Paleocene from the Eocene has clarified relations in the
northern Rocky Mountains and Great Plains, where the
two series have different depositional patterns and
areal distributions; it has also disposed of the so-called
"Laramie question" that had plagued American geology
since the days of the Hayden Survey (Merrill, 1906, p.
647-658), traces of which still lingered in 1932.
Many improvements have also been made in correla-
tion of the nonfossiliferous crystalline rocks, by means
of radiometric dating. Classification of the Precambrian
on the 1932 map was made on the basis of the now-
discredited "Archean" and "Algonkian" Systems, with
results that are no longer acceptable. The ages of
Phanerozoic plutons are now known with greater preci-
sion. The so-called "Carboniferous" granites shown in
the Southern Appalachians on the 1932 map are now
known to be of many Paleozoic ages, mostly pre-
Carboniferous. Similarly, the so-called "Jurassic" gra-
nites of the Western States are now known mainly to be
Cretaceous (for which no provision was made on the
1932 legend), and to be Jurassic only in small part.
The crystalline rocks of the Piedmont province were
poorly known in 1932, and only small parts of them had
been mapped in detail. By the time of compilation, Ar-
thur Keith's rendering of the province for the North
America map of 1912 was no longer useful, so Jonas
undertook a new reconnaissance. Because of the need to
cover a large area rapidly, her reconnaissance was
made on the basis of a general theory, outlined in a
contemporary journal article (Jonas, 1932). The theory
involved, among other things, correlation of large parts
of the Piedmont rocks with the Glenarm Series of sup-
posed "Algonkian" age (which had been studied in some
detail in Maryland and Pennsylvania) and a concept of
regional belts of retrogressive metamorphism above
throughgoing low-angle thrusts, in which the already-
formed crystalline rocks were further altered into
mylonites and diapthorites. The Piedmont province is
better known now as a result of extensive field surveys,
and only parts of these concepts have been substan-
tiated by later work; much greater complexity and
many more local peculiarities have been discovered.
Similar problems existed in New England in 1932,
where the sequences and ages of the crystalline rocks
were still unresolved over large areas, and where they
were considered to be largely Precambrian. B. K. Emer-
son (1917) had indeed made perceptive age assignments
in Massachusetts, but his rendering of this small area
had to be suppressed in favor of the overall picture.
Elsewhere in the country, large areas had already
been adequately portrayed on State Maps (at least for
purposes of the 1:2,500,000 scale), and few differences in
gross geologic patterns have arisen in the intervening
years. Differences in detail have resulted from changes
in stratigraphic classification, from greater precision in
surface mapping, and from more extensive subcrop data
in the heavily drift covered region of the Northern In-
THE GEOLOGIC MAP OF THE UNITED STATES
HISTORY OF THE PRESENT PROJECT
By 1955, it had become apparent that the Geologic
Map of the United States of 1932 had passed its peak of
usefulness, and plans were made by the U.S. Geological
Survey for a new and greatly revised map. Philip B.
King was asked to undertake this project, and facilities
for the work were set up at the Menlo Park office of the
A considerable interval elapsed, however, before the
project could be activated. King had to complete reports
on other projects, and he contributed much time to re-
viewing work that was being done by others who were
revising the Tectonic Map of the United States (Cohee,
1962) and the Geologic Map of North America (God-
dard, 1965). In preparation for the project, however, he
traveled widely in the United States to visit U.S.
Geological Survey field parties and to join formal
A further postponement occurred in 1960, during the
Twenty-first International Geological Congress in
Copenhagen, when the U.S. Geological Survey accepted
responsibility for preparing a Tectonic Map of North
America at the request of the Subcommission for the
Tectonic Map of the World. King was assigned the task
of compilation of this map; only after its completion, in
1967, could actual work on the Geologic Map of the
United States be started.
The long delay that followed inception of the project,
although unfortunate, resulted ultimately in a better
product. Acceptable modern geologic data for many
parts of the country did not become available until the
mid-196O's and even later. During the delay, new State
Maps were published covering extensive parts of the
country, and U.S. Geological Survey personnel com-
pleted new mapping of hitherto poorly known territory,
such as Nevada and eastern Oregon. Many more
radiometric dates became available, so age assignments
of the Precambrian rocks, the Phanerozoic plutons, and
the Cenozoic volcanics could be made with greater
Also, a competent staff had been assembled. Gertrude
J. Edmonston, who had assisted in completion of the
Tectonic Map of North America as geologic cartog-
rapher, continued these duties on the United States
map. Helen M. Beikman was enlisted as geologist and
fellow-compiler and prepared nearly half of the even-
A first draft of the compilation was nearly completed
early in 1970, after which Beikman left the project to
begin work on a companion Geologic Map of Alaska.
Several areas, however, were still left in a tentative
state or uncolored, pending receipt of additional infor-
mation, or further review of outstanding problems.
Final decisions on the Piedmont province, the State of
Texas, the Precambrian of the country, and the
Cenozoic volcanic rocks of the Western United States
were thus postponed.
In the last half of 1970 and during 1971 King and
Beikman traveled widely to obtain additional informa-
tion on these matters. Representation of the Precam-
brian was clarified at a Geological Society of America
Penrose Conference in Wyoming and during subse-
quent deliberations of a special panel on the Precam-
brian of the U.S. Geological Survey under the chair-
manship of Max D. Crittenden. A visit to the offices of
the Texas Bureau of Economic Geology was made to
complete the compilation for Texas, and several jour-
neys were made to the Southeastern States to obtain
data on the Piedmont Province. These journeys were
supplemented, especially for the Piedmont province, by
extensive correspondence and literature review. Data
on the volcanic rocks of the West were obtained mainly
from the Geological Survey staff at Menlo Park.
Geological plotting of the eastern half of the map was
completed in July 1971 and of the western half in Feb-
ruary 1972, after which each was reviewed by appro-
priate Survey geologists, whose corrections were incor-
porated in the final map. The completed map and legend
were transmitted for publication in midsummer of
1972, and a hand-colored manuscript copy formed a part
of the U.S. Geological Survey's exhibit at the Twenty-
fourth International Geological Congress in Montreal
in August l972.
SOURCES OF THE GEOLOGIC MAP
During the course of our compilation we consulted all
pertinent geologic maps and texts, including State
geologic maps. We also obtained large amounts of un-
published data, revisions, and criticisms from our col-
leagues on the staffs of the U.S. Geological Survey, the
State Geological Surveys, universities, and other re-
search institutions. To all these kind friends, col-
laborators, and contributors we express our deepest
thanks and appreciation.
The sources from which the map was compiled are
summarized below alphabetically by States and are
cited further at various places in the ensuing text. For
each State, the first entry is the most recently published
State Geologic Map, customarily on a scale of 1:250,000
or smaller. The data taken from all these maps, espe-
cially from the older ones, have been somewhat
modified and revised, those from the older maps the
most extensively, on the basis of sources listed in the
following order: (l) Regional maps on scales of
1:250,000 or smaller. (2) Detailed maps of quadrangles,
counties, or other small areas on scales of 1:24,000 to
1:62,500, which are summarized rather than
specifically cited. (3) Other maps and reports in geologi-
cal journals and elsewhere, published and unpublished.
(4) Significant reviews and corrections by U.S. Geologi-
cal Survey colleagues, and others.
Alabama.--Geologic Map of Alabama, 1926, by G. I.
Adams, Charles Butts, L. W. Stephenson, and C. W.
Cooke: Alabama Geological Survey, scale 1:500,000.
Northern Alabama Paleozoic area (including Valley and
Ridge province): Verified, or modified in detail from
county maps of Alabama Geological Survey published
after 1960. Piedmont province: Remapped from: R. D.
Bentley and T. L. Neathery, 1970, Geology of the Bre-
vard zone and related rocks of the Inner Piedmont of
Alabama: Alabama Geol. Society 8th Ann. Field Trip
Guidebook; approx. scale 1:500,000. Also manuscript
map of province furnished through the courtesy of P. E.
LaMoreaux, State Geologist, Alabama Geol. Survey,
1970; scale l:l,000,000. Coastal Plain: Revised from: W.
H. Monroe, 1945, Geologic map of the Upper Cretaceous
formations in central Alabama, in C. W. Carlston,
Ground-water resources of the Cretaceous area in
Alabama: Alabama Geol. Survey Spec. Rept. 18; scale
1:500,000. F. S. MacNeil, 1946, Geologic map of the
Tertiary formations of Alabama: U.S. Geol. Survey Oil
and Gas Inv. Prelim. Map 45; scale 1:500,000. Minor
data from county maps of Alabama Geol. Survey.
Arizona.--Geologic Map of Arizona, 1969, by E. D.
Wilson, R. T. Moore, and J. R. Cooper: U.S. Geol. Sur-
vey; scale 1:500,000. Radiometric dates of Precambrian
rocks compiled by Maureen G. Johnson, U.S. Geol. Sur-
Arkansas.--Geologic Map of Arkansas, 1929, edited
by H. D. Miser and G. W. Stose; scale 1:500,000.
Northwestern Paleozoic area: Manuscript map sum-
marizing data assembled for the new Geologic Map of
Arkansas, by B. R. Haley and E. R. Glick, U.S. Geol.
Survey; scale 1:2,500,000. Additional fault data from C.
G. Stone, Arkansas Geol. and Conserv. Div.
Southwestern Cretaceous and Tertiary area: Little
modified from map of 1929. Eastern Cenozoic area (Mis-
sissippi Embayment): Map showing Quaternary de-
posits, in manuscript 1971, by R. T. Saucier, Waterways
Exp. Sta., Vicksburg, Miss.; scale 1:1,000,000. Geologic
map (of) alluvial valley floor; sedimentary rocks under-
lying Recent alluvium, in H. N. Fisk, 1944, Geological
investigation of the alluvial valley of the lower Missis-
sippi River: Mississippi River Commission, Vicksburg,
Miss., pl. 10, sheet 1; scale 1:500,000; with modifications
from later data.
California.--Geologic Map of California, 1958-69, by
C. W. Jennings and others, California Div. Mines and
Geol., 2-degree atlas sheets; scale 1:250,000. Revisions
from: Geologic Map of California, in manuscript 1972,
by C. W. Jennings and others, California Div. Mines
and Geol.; scale 1:750,000. Maps and other data in: E. H.
Bailey, editor, 1966, Geology of northern California:
California Div. Mines and Geol. Bull. 190; and W. R.
Dickinson and Arthur Grantz, 1968, Proceedings of con-
ference on geologic problems of San Andreas fault sys-
tem: Stanford Univ. Pubs. Geol. Sci., v. 11. Also, P. E.
Hotz, 1971; Geology of lode gold deposits in the Klamath
Mountains, California and Oregon: U.S. Geol. Survey
Bull. 1290, pl. 1; scale 1:500,000. J. E. Evernden and R.
W. Kistler, 1970, Chronology of emplacement of
Mesozoic batholithic complexes in California and west-
ern Nevada: U.S. Geol. Survey Prof. Paper 623 (for
radiometric ages on plutonic rocks). Maps and other
data, partly unpublished, from P. E. Hotz, E. H. Bailey,
W. P. Irwin, L. D. Clark, P. C. Bateman, J. G. Vedder,
and T. W. Dibblee, Jr., of U.S. Geol. Survey, and B. M.
Page of Stanford University.
Colorado.--Geologic Map of Colorado, 1935, compiled
by W. S. Burbank, T. S. Lovering, E. N. Goddard, and E.
B. Eckel: U.S. Geol. Survey; scale 1:500,000. Geologic
maps of 2-degree quadrangles, scale 1:250,000, issued
as U.S. Geol. Survey Misc. Inv. Maps, as follows: Moab,
1964, by P. L. Williams, Map I-360; La Junta, 1968, by
G. R. Scott, Map I-629; Trinidad, 1969, by R. B. John-
son, Map I-558; Cortez, 1972, by D. D. Haynes and
others, Map I-629. Great Plains, eastern Colorado: Few
changes, except for revised age assignments. Rocky
Mountains and Colorado Plateau, western Colorado:
Compiled by Helen M. Beikman and Philip B. King
from published and unpublished data of U.S. Geol. Sur-
vey geologists. Radiometric ages of Precambrian rocks
and of Cretaceous-Tertiary instrusives from: Z. E.
Peterman and C.E. Hedge, 1968, Chronology of Pre-
cambrian events in the Front Range, Colorado: Cana-
dian Jour. Earth Sci., v. 5, no. 3, pt. 2, p. 749-756; and
written communications by Ogden Tweto. Final review
and correction of compilation by Ogden Tweto, U.S.
Geol. Survey, December 1971.
Connecticut.--See New England.
Florida.--Geologic Map of Florida, 1964, scale ap-
prox. 1:2,000,000, in H. S. Puri and R. O. Vernon, Sum-
mary of the geology of Florida and a guidebook to the
classic exposures: Florida Geol. Survey Spec. Pub. 5, pl.
2. Supplemented by Geologic Map of Florida, 1945, scale
1:1,000,000, in C. W. Cooke, Geology of Florida: Florida
Geol. Survey Bull. 29, pl. 1. Quaternary of northeastern
Florida adjusted from F.S. MacNeil, 1950, Pleistocene
shorelines of Florida and Georgia: U.S. Geol. Survey
Prof. Paper 221-F, pl. 1. Pliocene age assignment of
Caloosahatchee Formation of southern Florida from J.
E. Hazel, U.S. Geol. Survey, September 1971.
Georgia.--Geologic Map of Georgia, 1939, compiled
by C. W. Cooke, G. W. Crickmay, and Charles Butts:
Georgia Div. Mines, Mining, and Geol.; scale 1:500,000.
Valley and Ridge province, northwestern Georgia: Little
revision, but verified from county geologic maps of
Georgia Geol. Survey published after 1960. Blue Ridge
and Piedmont provinces: Compiled by Philip B. King
and Michael W. Higgins from large-scale published
maps of Georgia Geol. Survey, U.S. Geol. Survey, Coosa
Valley Planning and Devel. Comm., and Central
Savannah River Planning and Devel. Comm.; also
manuscript maps furnished through courtesy of Geor-
gia Geol. Survey; with extrapolations in intervening
areas. Published maps include: Western Piedmont by J.
S. Clarke, 1952; R. D. Bentley and T. L. Neathery, 1970
(see under Alabama); V. J. Hurst and T. L. Crawford,
1969; T. L. Crawford and J. H. Medlin, 1970. Central
Piedmont by L. A. Hermann, 1954; and M. W. Higgins,
1968. Eastern Piedmont by W. H. Grant, 1958; and T. L.
Crawford, 1968. Northeastern Blue Ridge by R. D.
Hatcher, Jr., 1971. Coastal Plain: F. S. MacNeil, 1947,
Geologic map of the Tertiary and Quaternary forma-
tions of Georgia: U.S. Geol. Survey Oil and Gas Inv.
Prelim. Map 72; scale 1:500,000. D. H. Eargle, 1955,
Stratigraphy of the outcropping Cretaceous rocks of
Georgia: U.S. Geol. Survey Bull. 1014, pl. 1, scale
1:500,000. Maps of seven counties in eastern Coastal
Plain by John Sandy, under direction of V. J. Hurst for
Central Savannah River Planning and Devel. Comm.,
Idaho.--Geologic Map of the State of Idaho, 1947,
compiled by C. P. Ross and J. D. Forrester: U.S. Geol.
Survey; scale 1:500,000. Extensively revised by Philip
B. King, as follows: Belt Supergroup and associated
rocks, northern Idaho: A. B. Griggs, 1975, Geologic map
of the Spokane quadrangle, Washington, Idaho, and
Montana: U.S. Geol. Survey Misc. Geol. Inv. Map I-768;
scale 1:250,000. Published geologic quadrangle maps by
J. E. Harrison and others, U.S. Geol. Survey, and syn-
thesis by Harrison. Anna Hietanen, 1962-68,
Metamorphic and igneous rocks along the northwestern
border zone of the Idaho batholith: U.S. Geol. Survey
Prof Paper 344-A-E; geologic maps on scale 1:48,000.
Idaho batholith and vicinity, west-central Idaho: Pub-
lished and unpublished maps by F. W. Cater, Jr., War-
ren Hamilton, B. F. Leonard, and D. L. Schmidt, U.S.
Geol. Survey; and R. R. Reid, Idaho Bur. Mines and
Geol. R. C. Newcomb, 1970, Tectonic structure of the
main part of the basalt of the Columbia River Group,
Washington, Oregon, and Idaho: U.S. Geol. Survey
Misc. Geol. Inv. Map I-587; scale 1:500,000.
Precambrian, Paleozoic, and Tertiary rocks, east central
Idaho: Published and unpublished maps by W. J. Mapel,
E. T. Ruppel, Betty A. L. Skipp, and others of U.S. Geol.
Survey. Robert Scholten and L. D. Ramspott, 1968, Tec-
tonic mechanism indicated by structural framework of
central Beaverhead Range, Idaho-Montana: Geol. Soc.
America Spec. Paper 104, pl. 1; scale 1:62,500. Upper
Cenozoic volcanic rocks, Snake River Plain: H. E. Malde,
1965, Snake River Plain, in H. E. Wright, Jr., and D. G.
Frey, editors, The Quaternary of the United States:
Princeton Univ. Press, p. 255-264, fig. 1, scale
1:1,583,000. H. E. Malde, H. A. Powers and C. H. Mar-
shall, 1965, Reconnaissance geologic map of west-
central Snake River Plain, Idaho: U.S. Geol. Survey
Misc. Geol. Inv. Map I-373; scale 1:125,000. Revisions
and corrections by H. E. Malde, U.S. Geol. Survey,
November 1970. Paleozoic, Mesozoic, and Tertiary
rocks, southeastern Idaho: Published and unpublished
geologic quadrangle maps by F. C. Armstrong, S. S.
Oriel, E. H. Pampeyan, D. E. Trimble, and others of
U.S. Geol. Survey, revising and extending earlier map-
ping by G. R. Mansfield and associates.
Illinois.--Geologic Map of Illinois, 1967, compiled by
H. B. Willman and others: Illinois Geol. Survey; scale
1:500,000. Time-stratigraphic units of Pennsylvanian
System according to: R. M. Kosanke and others, 1960,
Classification of the Pennsylvanian strata in Illinois:
Illinois Geol. Survey Rept. Inv. 214, pl. 1.
Iowa.--Geologic Map of Iowa, 1969: Iowa Geol. Sur-
vey; scale 1:500,000.
Indiana.--Map of Indiana Showing Bedrock Geology,
1970: Indiana Geol. Survey Misc. Map 16; scale
1:2,000,000. Minor modifications from 2-degree sheets
of Regional Geol. Map Series, partly in manuscript
1970, scale 1:250,000, supplied through courtesy of
Robert H. Shaver, Indiana Geol. Survey, November
Kansas.--Geologic Map of Kansas, 1964, compiled by
J. M. Jewett and others: Kansas Geol. Survey; scale
1:500,000. Supplemented by Geologic Map of Kansas,
1937, compiled by R. C. Moore, K. K. Landes, and
others; Kansas Geol. Survey; scale 1:500,000.
Kentucky.--Geologic Map of Kentucky, 1954: Ken-
tucky Geol. Survey Ser. 9; scale 1:1,000,000. Sup-
plemented by Geologic Map of Kentucky, 1929, by W. R.
Jillson: Kentucky Geol. Survey Ser. 6; scale 1:500,000.
Revised map compiled by Helen M. Beikman, using
where available 7 1/2-minute quadrangle maps, scale
1:24,000, published by U.S. Geol. Survey in 1962 and
later; and where not available the two State Maps.
Tertiary units of Mississippi Embayment from Geologic
Map of Jackson Purchase Region, Kentucky, 1972,
compiled by W. W. Olive, in Kentucky Geol. Society
Field Conf. Guidebook; scale 1:250,000.
Louisiana.--Generalized Geological Map of
Louisiana, 1959, L. W. Hough, State Geologist:
Louisiana Geol. Survey; scale approx. 1:1,500,000. Sup-
plemented by two earlier State Maps: Geologic Map of
State of Louisiana, 1946, compiled by W. E. Wallace,
Jr.: Shreveport Geol. Society; scale 1:500,000. Geologi-
cal Map of Louisiana, in manuscript 1948, compiled by
Rufus LeBlanc, Shell Oil Co.; scale 1:500,000.
Mississippi Embayment: Map showing Quaternary de-
posits, in manuscript 1971, by R. T. Saucier, Waterways
Exp. Sta., Vicksburg, Miss.; scale 1:1,000,000. Geologic
map (of) alluvial valley floor; sedimentary rocks under-
lying Recent alluvium, in H. N. Fisk, 1944, Geological
investigation of the alluvial valley of the Mississippi
River: Mississippi River Comm., Vicksburg, Miss., pl.
10, sheet 2: scale 1:500,000. Outcrops of Citronelle For-
mation (Pliocene): From J. A. Doering, 1956, Review of
Quaternary surface formations of Gulf Coast region:
Am. Assoc. Petroleum Geologists Bull., v. 40, p.
1816-l852, figs. 8-9. Outcrop areas of Midway Group:
Advice from H. B. Stenzel, written communication,
Maine.--See New England.
Maryland (and Delaware).--Geologic Map of Maryland, 1968, compiled
by K. N. Weaver and others: Maryland Geol. Survey; scale 1:250,000.
Supplemented by Map of Maryland (and Delaware) Showing Geological
Formations, 1933, E. B. Mathews, State Geologist:
Maryland Geol. Survey; scale 1:380,160. Valley and
Ridge provinces: Not revised. Piedmont province : Revi-
sions by M. W. Higgins, 1972, Age, origin, regional
relations, and nomenclature of Glenarm Series, central
Appalachian Piedmont; a reinterpretation: Geol. Soc.
America Bull., v. 83, p. 989-1026, especially pl. 1.
Coastal Plain of Maryland and Delaware: State Map
supplemented by Engineering Geology of the Northeast
Corridor, Washington, D.C., to Boston, Mass.; Coastal
Plain and surficial geology (compiled by J. P. Owens):
U.S. Geol. Survey Misc. Inv. Map I-514-B, sheets 2 and
3; scale 1:250,000.
Massachusetts.--See New England.
Michigan.--Bedrock of Michigan, 1968, compiled by
R. W. Kelley: Michigan Geol. Survey Small-Scale Map
2; scale 1:2,500,000. Precambrian in Northern Penin-
sula: Supplemented from: Centennial Geologic Map of
Michigan (Northern Peninsula), 1936, compiled by H.
M. Martin: Michigan Geol. Survey Pub. 39, Geol. Ser.
33; scale 1:500,000. Geologic Map of the Lake Superior
Region and Structure Sections, 1935, scale 1:1,000,000,
in C. K. Leith, R. J. Lund, and Andrew Leith, Precam-
brian rocks of the Lake Superior Region; a review of
newly discovered geologic features and a revised
geologic map: U.S. Geol. Survey Prof. Paper 184. R. W.
Bayley and W. R. Muehlberger, 1968, Basement rock
map of the United States (exclusive of Alaska and
Hawaii): U.S. Geol. Survey; scale 1:2,500,000.
Minnesota.--Geologic Map of Minnesota; bedrock
geology, 1970, by P. K. Sims: Minnesota Geol. Survey
Map M-14; scale 1:1,OOO,OOO. Representation of
Paleozoic formations in southeastern Minnesota sup-
plemented from: Geologic Map of Minnesota; St. Paul
Sheet, 1966, compiled by R. E. Sloan and G. S. Austin:
Minnesota Geol. Survey; scale 1:250,000.
Mississippi.--Geologic Map of Mississippi, 1969,
compiled by A. R. Bicker, Jr.: Mississippi Geol. Survey;
scale 1:500,000. With additional data from Geologic
Map of Mississippi, 1945, compiled by W. E. Belt and
others: U.S. Geol. Survey and Mississippi Geol. Society;
Missouri.--Geologic Map of Missouri, 1961, compiled
by M. H. McCracken and others: Missouri Div. Geol.
Survey and Water Res.; scale 1:500,000.
Montana.--Geologic Map of Montana, 1955, compiled
by C. P. Ross, D. A. Andrews, and I. J. Witkind: U.S.
Geol. Survey; scale 1:500,000. Great Plains, eastern
Montana: No revisions of State Map. Rocky Mountains,
western Montana: New compilation by Philip B. King
and Helen M. Beikman, from following sources: Belt
Supergroup and associated rocks, northwestern Mon-
tana: Geologic quadrangle maps by A. B. Campbell, J.
E. Harrison, M. R. Mudge, W. H. Nelson, and others of
U.S. Geol. Survey, and W. M. Johns, Montana Bur.
Mines and Geol. Correlations by A. G. Smith and W. C.
Barnes, 1966, Correlation and facies changes in the
carbonaceous, calcareous, and dolomitic formations of
the Belt-Purcell Supergroup: Geol. Soc. America Bull.,
v. 77, p. 1399-1426. Radiometric dates from J. D.
Obradovich and Z. E. Peterman, 1968, Geochronology of
the Belt Series, Montana: Canadian Jour. Earth Sci., v.
5, no. 3, pt. 2, p. 737-747. Synthesis by J. E. Harrison,
U.S. Geol. Survey. Boulder batholith and vicinity,
central-western Montana: Geologic quadrangle maps by
M. R. Klepper, G. D. Robinson, E. T. Ruppel, Betty A. L.
Skipp, H. W. Smedes, and others of U.S. Geol. Survey
and J. C. Maxwell and others of Princeton University.
Summarized in part by G. D. Robinson, M. R. Klepper,
and J. D. Obradovich, 1970, Overlapping plutonism,
volcanism, and tectonism in the Boulder batholith re-
gion, western Montana, in R. R. Coats, R. L. Hay, and C.
A. Anderson, editors, Studies in volcanology: Geol. Soc.
America Mem. 116, p. 557-576. Southwestern Mon-
tana: Published and unpublished quadrangle maps by
H. L. James, J. B. Hadley, W. B. Meyers, I. J. Witkind,
and others of U.S. Geol. Survey. Robert Scholten and
others, 1955, Geology of the Lima region, Montana and
Idaho: Geol. Soc. America Bull., v. 66, p. 345-404, pl. 1;
scale approx. 1:125,000. Precambrian radiometric dates
compiled by Maureen G. Johnson, U.S. Geol. Survey;
Precambrian geology reviewed by H. L. James, U.S.
Nebraska.--Geologic Bedrock Map of Nebraska,
1969, compiled by R. R. Burchett: Nebraska Geol. Sur-
vey; scale 1:1,000,000.
Nevada.--No adequate published State Map availa-
ble. Compiled by Philip B. King from: Manuscript
sheets for Geologic Map of Nevada, by J. H. Stewart and
J. E. Carlson, U.S. Geol. Survey, in preparation 1974;
scales 1:250,000 and 1:500,000. County geologic maps
by geologists of U.S. Geol. Survey and Nevada Bur.
Mines, published since 1960 as Nevada Bur. Mines Bul-
letins, as U.S. Geol. Survey Misc. Inv. Maps, or in man-
uscript; scale 1:250,000.
New England.--Compiled by Philip B. King from:
State Geologic maps: Preliminary Geologic Map of
Maine, 1967, compiled by A. M. Hussey II and others:
Maine Geol. Survey; scale 1:500,000. Geologic Map of
New Hampshire, 1955, compiled by M. P. Billings: U.S.
Geol. Survey; scale 1:250,000. Centennial Geologic Map
of Vermont, 1961, compiled by C. G. Doll and others:
Vermont Geol. Survey; scale 1:250,000. Geologic Map of
Massachusetts and Rhode Island, 1917, in B. K. Emer-
son, Geology of Massachusetts and Rhode Island: U.S.
Geol. Survey Bull. 597; scale 1:250,000. Bedrock
Geologic Map of Rhode Island, 1971 in A. W. Quinn,
Bedrock geology of Rhode Island: U.S. Geol. Survey
Bull. 1295; scale 1:125,000. Preliminary Geologic Map
of Connecticut, 1956, compiled by John Rodgers and
others: Connecticut Geol. and Nat. Hist. Survey; scale
1:253,440. With modifications from: (l) 7 1/2-minute
geologic quadrangle maps in Massachusetts, Rhode Is-
land, and Connecticut, mostly published by U.S. Geol.
Survey; scale 1:24,000. (2) New England Intercollegiate
Geol. Conf. Guidebooks, especially for Connecticut val-
ley of Massachusetts, 1967; New Haven, Connecticut,
and vicinity, 1969; and Rangely Lakes-Dead River
Basin region, Maine, 1970. (3) Articles and maps in:
E-an Zen, W. S. White, J. B. Hadley, and J. B. Thomp-
son, Jr., editors, 1968, Studies of Appalachian geology;
Northern and Maritime: Interscience Pub., New York;
especially on nappes and gneiss domes in New Hamp-
shire, Massachusetts, and eastern Connecticut (J. B.
Thompson, Jr., and others; H. R. Dixon and L. W.
Lundgren, Jr.) and on Maine (P. H. Osberg and others;
J. C. Green and V. C. Guidotta; A. M. Hussey II). (4)
Manuscript maps on northern and southeastern Maine,
supplied by Louis Pavlides, E. L. Boudette, D. B.
Stewart, and D. R. Wones; distribution of Paleozoic vol-
canic rocks in New England, compiled by D. W. Rankin;
all of U.S. Geol. Survey, 1971. (4) Radiometric dates in
eastern Massachusetts and vicinity from R. E. Zartman
and R. F. Martin, 1971, Radiometric age (Late Ordovi-
cian) of the Quincy, Cape Ann, and Peabody Granites
from eastern Massachusetts: Geol. Soc. America Bull.,
v. 82, p. 937-958; also oral communications from R. E.
Zartman, 1971. Original compilations reviewed and
corrected by: John Rodgers of Yale University and
James Skehan of Boston College, 1969 and 1971; and by
K. G. Bell, H. R. Dixon, Richard Goldsmith, D. S. Har-
wood, N. L. Hatch, L. R. Page, D. W. Rankin, E-an Zen,
and others of U.S. Geol. Survey, 1971.
New Hampshire.--See New England.
New Jersey.--Geologic Map of New Jersey, 1910-12
(reprinted 1950), by J. V. Lewis and H. B. Kmmel: New
Jersey Dept. Cons. and Econ. Devel. Atlas Sheet 40;
scale 1:250,000. With revisions as follows: Precambrian
and Paleozoic of Reading Prong: A. A. Drake, Jr., 1970,
Structural geology of the Reading Prong, in G. W.
Fisher, F. J. Pettijohn, J. C. Reed, Jr., and K. N. Weaver,
editors, Studies in Appalachian geology; Central and
Southern: Interscience Pub., New York, p. 271-291.
Also manuscript map by A. A. Drake, Jr., U.S. Geol.
Survey, June 1971; scale 1:1,000,000. Coastal Plain:
Engineering geology of the Northeast Corridor,
Washington, D.C., to Boston, Mass.; Coastal Plain and
surficial geology (compiled by J. P. Owens): U.S. Geol.
Survey Misc. Inv. Map I-514-B, sheet 1, 1967; scale
New Mexico.--Geologic Map of New Mexico, 1965, by
C. H. Dane and G. O. Bachman: U.S. Geol. Survey; scale
1:500,000. With additions and modifications from vari-
ous sources, including: Subdivisions of Precambrian,
Preliminary geologic and relief map of the Precambrian
rocks of New Mexico, 1961, by R. W. Foster and T. F.
Stipp: New Mexico Bur. Mines and Min. Res. Circ. 57;
scale 1:500,000. Faults and other tectonic features from
maps by V. C. Kelley and others, such as: Upper Rio
Grande area, 1954, U.S. Geol. Survey Oil and Gas Inv.
Map OM-157; Ruidoso-Carrizozo area, 1964, New Mex-
ico Geol. Society 15th Field Conf.; Zuni-Defiance region,
1967, New Mexico Geol. Society, 18th Field Conf. Com-
pilation reviewed by G. 0. Bachman, U.S. Geol. Survey,
New York.--Geologic Map of New York, 1962, com-
piled by J. G. Broughton, D. W. Fisher, Y. W. Isachsen,
and L. V. Rickard: New York State Mus. and Sci. Serv.,
Geol. Survey Map and Chart Ser. 5; scale 1:250,000.
Taconic region of eastern part of State revised from
E-an Zen, 1967, Time and space relationships of the
Taconic allochthon and autochthon: Geol. Soc. America
Spec. Paper 97, pl. 1; scale approx. 1:500,000.
North Carolina:--Geologic Map of North Carolina,
1958, J. L. Stuckey, State Geologist: North Carolina
Div. Min. Res.; scale 1:500,000. Coastal Plain: No revi-
sions. Blue Ridge and Piedmont provinces: Extensively
revised from many sources, including: J. B. Hadley and
A. E. Nelson, 1971, Geologic Map of the Knoxville
Quadrangle, North Carolina, Tennessee, and South
Carolina: U.S. Geol. Survey Misc. Inv. Map I-654; scale
1:250,000. D. W. Rankin and G. H. Espenshade, 1972,
Geologic Map of the Abingdon Quadrangle, Virginia,
North Carolina, and Tennessee, western half: U.S.
Geol. Survey Misc. Inv. Map I-709-A; scale 1:250,000
(eastern half in manuscript). J. R. Conley and G. L.
Bain, 1965, Composite geologic map of the Carolina
Slate Belt in North Carolina, west of the Deep River
-Wadesboro Triassic basin: Southeastern Geol., v. 6,
no. 8; scale approx. 1:500,000. J. M. Parker III, 1968,
Structure of easternmost North Carolina Piedmont:
Southeastern Geol., v. 9, no. 3; scale approx. 1:500,000;
and written communications from Parker, May 1971.
Maps and articles by J. B. Hadley, D. W. Rankin, J. C.
Reed, Jr., and others, in G. W. Fisher, F. J. Pettijohn, J.
C. Reed, Jr., and K. N. Weaver, editors, 1970, Studies of
Appalachian geology; Central and Southern: Intersci-
ence Pub., New York. Radiometric and other age data
on plutons in North Carolina, South Carolina, and east-
ern Georgia, from: P. D. Fullagar, 1971, Age and origin
of plutonic intrusions in the Piedmont of the southeast-
ern Appalachians: Geol. Soc. America Bull., v. 82, p.
2845-2862. J. R. Butler, 1972, Age of Paleozoic reg-
ional metamorphism in the Carolinas, Georgia, and
Tennessee: Am. Jour. Sci., v. 272, p. 319-333. Also writ-
ten communications from Fullagar and Butler, 1971.
North Dakota.--Bedrock Geologic Map of North
Dakota, 1969, compiled by C. G. Carlson: North Dakota
Geol. Survey Misc. Map 10; scale 1:1,000,000.
Ohio.--Geologic Map of Ohio, 1920 (reprinted 1947),
by J. A. Bownocker: Ohio Geol. Survey; scale 1:500,000.
Subcrop extent of Silurian subdivisions and other fea-
tures revised by Arie Janssens of Ohio Geol. Survey,
written communication, December 1970. Minor revi-
sions of other areas from published county and quad-
rangle maps of Ohio Geol. Survey and U.S. Geol. Sur-
Oklahoma.--Geologic Map of Oklahoma, 1954, by H.
D. Miser: U.S. Geol. Survey; scale 1:500,000.
Oregon.--Western half: Geologic Map of Oregon west
of 121st Meridian, 1961, by F. G. Wells and D. L. Peck:
U.S. Geol. Survey; scale 1:500,000. Klamath Mountains
area revised from: P. E. Hotz, 1971, Geology of lode gold
deposits in the Klamath Mountains, California and
Oregon: U.S. Geol. Survey Bull. 1290, pl. 1; scale
1:500,000. R. G. Coleman, 1972, The Colebrooke Schist
of southwestern Oregon and its relation to the tectonic
evolution of the region: U.S. Geol. Survey Bull. 1339, pl.
1; scale 1:125,000. Eastern half: Geologic Map of Oregon
East of 121st Meridian, in preparation 1974, compiled
by G. W. Walker: U.S. Geol. Survey; scale 1:500,000.
Also covered in part by earlier published 2-degree
geologic quadrangle maps by G. W. Walker and others:
U.S. Geol. Survey Misc. Inv. Maps; scale 1:250,000.
Generalizations by Philip B. King, assisted by G. W.
Pennsylvania.--Geologic Map of Pennsylvania, 1960,
compiled by Carlyle Gray and others: Pennsylvania
Topog. and Geol. Survey; scale 1:250,000. Reading
Prong of eastern Pennsylvania revised from manuscript
map by A. A. Drake, Jr., U.S. Geol. Survey, June 1971;
Rhode Island.--See New England.
South Carolina.--No adequate published State Map
available; partial maps as follows: W. C. Overstreet and
Henry Bell III, 1965, Geologic map of the crystalline
rocks of South Carolina: U.S. Geol. Survey Misc. Inv.
Map I-413; scale 1:250,000. W. C. Overstreet and Henry
Bell III, 1965, Geologic map and inferred age relations
of the crystalline rocks of South Carolina, in The crys-
talline rocks of South Carolina; U.S. Geol. Survey Bull.
1183, pl. 1; scale 1:500,000. C. W. Cooke, 1936, Cretace-
ous and Tertiary formations of South Carolina, in Geol-
ogy of the Coastal Plain of South Carolina: U.S. Geol.
Survey Bull. 867, pl. 2; scale 1:500,000. Piedmont pro-
vince: Extensively revised from publications of South
Carolina State Devel. Board Div. of Geol., including:
Detailed maps by R. D. Hatcher, Jr., and V. S. Griffin,
Jr., in north-western South Carolina, and reconnais-
sance maps elsewhere. County and quadrangle maps by
D. T. Secor, H. D. Wagener, J. R. Butler, J. F. McCauley,
and others. Coastal Plain: Revised from data compiled
by S. D. Heron for Geological Highway Map of the
Mid-Atlantic Region, 1970: Am. Assoc. Petroleum
Geologists Geologic Highway Map Ser. 4; scale approx.
South Dakota.--Geologic map (of) South Dakota,
1953, compiled by B. C. Petsch: South Dakota Geol.
Survey; scale 1:500,000. Supplemented by Geologic
Map of South Dakota, 1951, compiled by N. H. Darton:
U.S. Geol. Survey; scale 1:500,000. Subdrift geology
east of Missouri River from R. F. Flint, 1955, Pleis-
tocene geology of eastern South Dakota: U.S. Geol. Sur-
vey Prof Paper 262, fig. 4. Precambrian of Black Hills
area revised from data of R. W. Bayley, U.S. Geol. Sur-
vey open-file map, 1972.
Tennessee.--Geologic Map of Tennessee, 1966, by W.
D. Hardeman, R. A. Miller, and G. D. Swingle; Tennes-
see Div. Geol.; scale 1:250,000. Tertiary units of Missis-
sippi Embayment area, western Tennessee, revised by
W. S. Parks, Water Resources Div., U.S. Geol. Survey,
written communication, November 1971.
Texas.--Geologic Map of Texas, 1937, by N. H. Dar-
ton, L. W. Stephenson, and Julia Gardner: U.S. Geol.
Survey; scale 1:500,000. Extensively revised as follows
(letter symbols refer to [FIG_6]): (A) Eastern, northern,
and westernmost Texas, where available, from sheets of
Geologic Atlas of Texas, 1965-72, by V. E. Barnes and
others: Texas Univ. Bur. Econ. Geology; scale
1:250,000. (B) Llano region, central Texas, from manu-
script maps by V. E. Barnes, F. B. Plummer, and others,
Texas Univ. Bur. Econ. Geology; scales 1:125,000 and
1:250,000. (C) Edwards Plateau region from manuscript
maps by F. E. Lozo, Jr., Shell Oil Co.; scale 1:250,000.
(D) South Texas Coastal Plain compiled by Helen M.
Beikman from manuscript data for Geologic Atlas of
Texas; manuscript maps by D. H. Eargle, U.S. Geol.
Survey; Geologic Map of Texas, 1937; and other sources.
(E) Trans-Pecos region compiled by Philip B. King from
published quadrangle maps of Texas Univ. Bur. Econ.
Geology and U.S. Geol. Survey, and from personal
knowledge. (F) Northwestern Texas, where not other-
wise covered, from Geologic Map of Texas, 1937, with
revisions of Paleozoic area by D. H. Eargle, U.S. Geol.
Utah.--Geologic Map of Utah, 1961-63, compiled by
W. L. Stokes, J. H. Madsen, Jr., and L. F. Hintze: Utah
State Land Board and Univ. of Utah; scale 1:250,000.
With additions and corrections by M. D. Crittenden and
H. T. Morris, U.S. Geol. Survey, 1970-71.
Vermont.--See New England.
Virginia.--Geologic Map of Virginia, 1963, compiled
by R. C. Milici, C. T. Spiker, Jr., and J. M. Wilson:
Virginia Div. Min. Res.; scale 1:500,000. Valley and
Ridge and Blue Ridge provinces.--Minor revisions only.
Piedmont province.--Extensive revisions as follows:
North of James River revised by M. W. Higgins from
maps by D. L. Southwick, J. C. Reed, Jr., S. K. Neuschel,
and others, and by extrapolations based on reconnais-
sance. South of James River revised in part by Philip B.
King from published and unpublished maps by D. W.
Rankin, G. H. Espenshade, J. F. Conley, O. T. Tobisch,
and Lynn Glover III. Coastal Plain.--No revision.
Washington.--Geologic Map of Washington, 1961,
compiled by M. T. Huntting, W. A. Bennett, V. E.
Figure 6 [FIG_6].--Index map of Texas, showing areas covered by different
sources used on the Geologic Map. Letter symbols are explained on
Livingston, Jr., and W. S. Moen: Washington Div.
Mines and Geol.; scale 1:500,000. Extensively revised
by Philip B. King, as follows: Olympic Peninsula,
northwestern Washington: From published and unpub-
lished maps by W. M. Cady, R. W. Tabor, H. D. Gower, P.
D. Snavely, Jr., and others of U.S. Geol. Survey. Coast
Ranges, southwestern Washington: From published
quadrangle maps by Holly Wagner, E. H. Wolfe, H. D.
Gower, P. D. Snavely, Jr., and others, U.S. Geol. Survey.
Volcanic rocks, southern Cascade Range: Revised by C.
A. Hopson, Univ. of California, Santa Barbara, written
communication, February 1972. Prevolcanic rocks,
northern Cascade Range: Peter Misch, 1966, Tectonic
evolution of northern Cascades of Washington State, in
Symposium on the tectonic history and mineral deposits
of the western Cordillera: Canadian Inst. Min. and
Geol. Spec. Volume 8, p. 101-148. Maps and other data,
in part unpublished, by D. F. Crowder, F. W. Cater, R.
W. Tabor, and C. A. Hopson. Northern and northeastern
Washington: A. B. Griggs, 1966, Geologic map of west-
ern half of Spokane quadrangle, Washington and Idaho:
U.S. Geol. Survey Misc. Geol. Inv. Map I-464; scale
1:250,000. General and detailed maps, in part unpub-
lished, by C. D. Rinehart, J. F. Fox, Jr., R. G. Yates, F.
K. Miller, G. E. Becraft, and others, U.S. Geol. Survey.
Columbia Plateau: R. C. Newcomb, 1970, Tectonic
structure of the main part of the basalt of the Columbia
River Group, Washington, Oregon, and Idaho: U.S.
Geol. Survey Misc. Geol. Inv. Map I-587; scale
West Virginia.--Geologic Map of West Virginia,
1968, compiled by D. H. Cardwell, R. B. Erwin, and H. P.
Woodward: West Virginia Geol. and Econ. Survey; scale
Wisconsin.--Geologic Map of Wisconsin, 1949, Wis-
consin Geol. and Nat. Hist. Survey; scale 1:1,000,000.
Precambrian rocks, edge of Cambrian overlap, and
faults revised from: C. E. Dutton and R. F. Bradley,
1970, Lithologic, geophysical, and mineral commodity
maps of Precambrian rocks of Wisconsin: U.S. Geol.
Survey Misc. Geol. Inv. Map I-631; scale 1:500,000;
especially sheets 3 and 5. In the main Precambrian area
of northern Wisconsin, contacts of Precambrian units
extrapolated by Philip B. King beyond their extent as
mapped by Dutton and Bradley.
Wyoming.--Geologic Map of Wyoming, 1955, com-
piled by J. D. Love, J. L. Weitz, and R. K. Hose: U.S.
Geol. Survey; scale 1:500,000. Revised in part, as fol-
lows: Precambrian rocks from published and unpub-
lished data by R. W. Bayley, Harry Granger, R. C.
Pearson, and others, U.S. Geol. Survey, and R. S. Hous-
ton, Univ. of Wyoming. Heart Mountain fault, north-
western Wyoming: From W. G. Pierce, U.S. Geol. Sur-
vey, 1972. Volcanic rocks, Yellowstone National Park:
From Geologic Map of Yellowstone National Park,
1972, by geologists of U.S. Geol. Survey: U.S. Geol.
Survey Misc. Geol. Inv. Map I-711; scale 1:125,000. W.
R. Keefer, 1972, The geological story of Yellowstone
National Park: U.S. Geol. Survey Bull. 1374, pl. 1; scale
approx. 1:500,000; and written communication from R.
L. Christiansen, U.S. Geol. Survey, November 1970.
Tertiary sedimentary rocks revised by J. D. Love, writ-
ten communication, January 1971. Compilation of
Wyoming reviewed by J. D. Love, U.S. Geol. Survey,
and staff of Dept. Geol., Univ. of Wyoming, written
communication, January 1971.
Phanerozoic metamorphism.--Areas of Phanerozoic
metamorphism in western United States, from many
sources; in Appalachian region from B. A. Morgan,
1972, Metamorphic map of the Appalachians: U.S. Geol.
Survey Misc. Geol. Inv. Map I-724; scale 1:2,500,000.
Limits of Pleistocene glacial deposits.--Glacial Map of
the United States East of the Rocky Mountains, 1959, R.
F. Flint, chairman, Geol. Soc. America; scale
1:1,750,000. Major revisions, based on later data, made
by Roger B. Morrison, U.S. Geol. Survey, 1974, as fol-
lows: Montana and North Dakota from R. W. Lemke
and R. B. Colton. South Dakota, Nebraska, Kansas,
Missouri, and Iowa from the respective State Geological
Surveys. Indiana from R. V. Ruhe, Indiana University.
Ohio and Kentucky from Jane L. Forsyth, Bowling
Green State University. Pennsylvania, New Jersey,
and New York from C. S. Denny, U.S. Geol. Survey.
Subsea bathymetry.--Subsea contours compiled by
Philip B. King and Gertrude J. Edmonston from the
following sources, the locations of which are indicated
in [FIG_7]: (l) and (2) International map of the World,
United States, scale 1:1,000,000, by the U.S. Geol. Sur-
vey. Sheet NL-10, Cascade Range, 1951. Sheet NK-10,
Mount Shasta, 1951. Sheet NI-11, Los Angeles, 1952.
Subsea contours in metres. (3) State of California, base
map with shaded relief and offshore contours, by the
U.S. Geol. Survey, 1968, scale 1:1,OOO,OOO. Contours in
fathoms, converted to metres. (4) D. C. Krause, 1965,
Tectonics, bathymetry, and geomagnetism of the south-
ern continental borderland west of Baja California,
Mexico: Geol. Soc. America Bull., v. 76, fig. 1, p. 260.
Mercator projection; contours in metres. (5) and (6)
Bathymetry of the northeast Pacific, by Scripps Institu-
tion of Oceanography and Underseas Surveillance
Oceanographic Center, 1970. Sheets l and 2. Mercator
projection; contours in fathoms converted to metres. (7)
Submarine topography of the Gulf of California by R. L.
Fisher, G. A. Rusnak, and F. P. Shepard, in T. H. van
Andel and G. G. Shor, Jr., editors, Marine geology of the
Gulf of California: Am. Assoc. Petroleum Geologists
Mem. 3, 1964. Mercator projection; contours in fathoms,
converted to metres. (8) Elazar Uchupi, 1968, Map
showing relation of land and submarine topography.
Mississippi Delta to Bahia de Campeche; U.S. Geol.
Survey Misc. Inv. Map I-521. Elazar Uchupi, 1966, Map
showing relation of land and submarine topography, De
Soto Canyon to Great Bahama Bank: U.S. Geol. Survey
Misc. Geol. Inv. Map I-475. Both maps, scale
1:1,000,000, contours in metres. (9) Elazar Uchupi,
1965, Map showing relation of land and submarine to-
pography, Nova Scotia to Florida: U.S. Geol. Survey
Misc. Geol. Inv. Map I-451. Scale 1:1,000,000, contours
in metres. (1O) R. M. Pratt, 1968, Physiography and
sediments of the deep-sea basin, in Atlantic continental
shelf and slope of the United States: U.S. Geol. Survey
Prof Paper 529-B, pl. 1. Mercator projection, contours
in metres. (11) U.S. Naval Oceanographic Service, Con-
toured position plotting sheet BG-895. Mercator projec-
tion; contours in fathoms, converted to metres.
USES OF THE GEOLOGIC MAP
Sometimes, when we explain to nongeologists our
project for a Geologic Map of the United States, we are
dismayed when asked, "What good is it?" We compilers,
enmeshed in our many problems of assembling, collat-
ing, and generalizing the source data for the map, find it
difficult to produce a ready answer to this question.
Nevertheless, the values and uses of an accurate
Geologic Map of the United States are manifold, not
only to geologists, but to the public at large.
First of all, of course, the map displays the rocky
foundations on which our country is built and is a sum-
mation of the nearly two centuries of investigation of
this foundation by a succession of geologists. It is thus a
reference work that present and future geologists of the
country can consult and is of prime importance in the
education of earth scientists in schools and colleges.
Further, it can be consulted by geologists in other coun-
tries and continents who wish to learn about the geol-
ogy of the United States; they will compare the map
with similar national or continental maps of their own
In terms of resources useful to man, the Geologic Map
lays out accurately the major regions of bedrock in the
United States upon which many facets of our economy
depend. It illustrates the areas of stratified rocks that
are the sources of most of our fuels, and the areas of
crystalline, plutonic, and volcanic rocks that contain
important parts of our mineral wealth. The map shows
areas of complex folding and faulting, parts of which are
still tectonically unstable and subject to earthquake
hazards. To some extent the bedrock represented on the
map also influences the surface soils, which are of in-
terest in agriculture and engineering works.
Beyond this, the practical value of the map is less
tangible, although it can be an important tool for the
discerning user. Clearly, the map will not pinpoint the
location of the next producing oil well or the next
bonanza mine, nor will it give specific advice for the
location of a dam or a reactor site; these needs can only
be satisfied on maps on much larger scales, designed for
specific purposes. Nevertheless, the sapient exploration
geologist can find upon it significant regional features
not apparent to the untrained user. Many great petro-
leum pools occur in stratigraphic traps, or "wedge belts
of porosity," caused by overlap or truncation, the reg-
ional occurrence of which can be seen on the map. Im-
portant mineral deposits cluster along regional tectonic
trends or chains of plutons of specific ages. Finally, the
Geologic Map will be used in national planning ac-
tivities in conjunction with other national maps show-
ing environmental features such as climate, vegetation,
and land use--for the location of power transmission
corridors, highways, National Parks, wilderness areas,
reclamation projects, and the like.
METHODS OF COMPILATION
Many people, including a surprising number of
trained geologists, ask the question: How does one go
about compiling a geologic map of the United States (or
any small-scale regional geologic map)? No doubt vari-
ous methods of compilation are possible, yet some gen-
eral principles apply to all, if an acceptable product is to
be obtained. We can explain our own methods, which we
have evolved through trial and error.
First of all, compilation involves geological com-
prehension and human skill; no mechanical shortcuts
Figure 7 [FIG_7].--Index map of the United States, showing areas covered by
the different sources used for the subsea contours on the Geologic Map.
Numbers are explained on page 18.
are possible. High-altitude or satellite imagery is un-
doubtedly valuable for interpreting the geology of other
planets, or even of poorly known regions of the earth,
but it is merely of peripheral interest in regions where
large amounts of ground data are available, as in the
United States. Such images illustrate the broad
geomorphic features and tectonic lineaments, but they
reveal little of the nature, relations, or sequences of the
rocks from which these features are made; also, in the
United States, wide areas covered by the imagery show
more of the soil, vegetation, and the works of man than
of the fundamental geology. Further, there appears to
be little value in reducing large-scale data into small-
scale data by computer. We are not familiar with the
details of research that has been done on this matter,
but it is our impression that the computer simply re-
duces selected lines from the source maps in a manner
that could be done as well by photography. Precision of
linework is attained, but there is no generalization that
would make the product comprehensible.
We begin instead, where possible, with geologic
source maps on medium scales, approximately between
1:500,000 and 1:250,000, or five to ten times our final
scale of 1:2,500,000 [FIG_8ab][FIG_8c]. A certain amount of
generalization has already been made on these
medium-scaled geologic maps, yet they still retain
much of the original geology in manageable form.
Where only the raw geologic data are available, on
scales of 1:24,000 to 1:62,500, it has been necessary for
us to make our own generalization to the medium scale
before proceeding further. On the other hand, source
materials on scales of 1:1,000,000 or smaller are ordi-
narily ill adapted for our purpose, unless they cover
areas of very simple geology. On these, the hand of
another compiler has been interposed between us and
the sources; we must accept on faith his judgment as to
what should be represented rather than making judg-
ments of our own.
Beginning with the ideal medium-scaled source
maps, we make an effort to comprehend the geological
meaning of the area represented--its geologic history,
stratigraphy, and tectonics--in order to determine
what features can most appropriately be selected for use
on the final map. We then trace these features on clear
plastic. Some items on the original maps can easily be
sacrificed, such as subdivisions within gross strati-
graphic units, convolutions of contacts produced by ero-
sion or topography, little faults unrelated to the gross
tectonic pattern, patches of some ubiquitous lava or
gravel scattered over bedrock, and strips of river al-
luvium. Other items should be emphasized or even ex-
aggerated, such as inliers of Precambrian rocks amidst
younger rocks, and the lay of formations and contacts
produced by folding and faulting.
Something should be said about the rock units
selected for tracing. The compiler of each State Map or
other source map classifies the rocks in a manner most
appropriate for his area, but which may be inappro-
priate for an adjoining State or area. In compiling a
Geologic Map of the United States it would be a simple
matter merely to accept and copy without coordination
the classifications in the different areas, but this would
not result in a meaningful representation for the whole
country. The compiler of a national map must therefore
have in mind what he wishes to achieve in a unified
classification for the country and make his tracings
accordingly--although this tentative classification may
have to be more or less modified as the work proceeds.
These tracings are then reduced photographically
and replotted. Ordinarily the reduction is to some in-
termediate scale--1:1,000,000 in regions of complex
geology, and 1:2,000,000 in regions of simpler geology.
The results are expressive for their scales, but when a
further reduction is made to the final 1:2,500,000 scale,
it is obvious that still greater sacrifices will be neces-
The final generalization is always painful to the com-
piler, because he is thoroughly aware of the significant
geological features he wishes to portray, yet has very
little space in which to do so. He is constrained by the
limits of legible printing of lines and colors, and by the
eventual user's limits of comprehension. Reduction and
generalization of the geology to the 1:2,500,000 scale
brings it down to about the limit at which actual ground
features can be represented; on smaller scales the com-
piler must indulge in fantasy. On the 1:2,500,000 scale
he must endeavor to retain some grasp of reality and to
present a digest of the significant aspects of the geology.
For some complex areas this is not possible, even on
the 1:2,500,000 scale. For these areas King recalls the
sage advice of Nelson Horatio Darton, a master com-
piler of an earlier generation: Do not attempt to show
details of geologic pattern or structure; show merely
"what is there"--patches of the significant formations,
not necessarily arranged in any meaningful picture. In
parts of the United States Map, especially in the Basin
and Range province of the Western States, we reluc-
tantly have cast our ideals aside and resorted to this
drastic procedure, producing within the mountain
ranges a crazy quilt of colored patches of selected units,
leaving the user to consult maps on larger scales for the
CONTENTS OF THE GEOLOGIC MAP
The present Geologic Map of the United States fol-
lows the same format as the preceding Geologic Map of
the United States of 1932. Ideally, both have been de-
signed to represent the geological features that the user
could find if he should visit any locality within its limits,
that is, the bedrock formations that lie at the surface at
that locality. In many parts of the country, especially in
the arid regions of the Southwest, this is literally true.
In other parts of the country there are lesser or greater
departures from this ideal, owing mainly to conceal-
ment of the bedrock by surficial material.
Thus, the geologic map is primarily a bedrock map
and not a surficial geology map. Surficial geology maps
represent in much detail the surface geology and mater-
ials, mainly of Quaternary age, that overlie the bedrock
and classify them as to kind and origin. Bedrock is
shown, at most, only in actual outcrops; hence, these
maps can give little hint as to the fundamental bedrock
pattern and structure. Making a surficial geology map
is a worthy enterprise in itself but one with which we
are not involved; such maps of all or large parts of the
country have already been prepared by others (Thorp
and Smith, 1952; Flint, 1959).
Consequently, the Geologic Map of the United States
does not represent the glacial and other deposits of
Pleistocene age that blanket large parts of the Northern
Interior States, and loess or drifted sand which are
extensive in other places. In such areas our representa-
tion of the bedrock must perforce be a subcrop or sub-
drift map sometimes based more on the results of drill-
ing and geophysical data than on outcrops. In the
Northern Interior States we have marked the limits of
the later and earlier glaciations to suggest areas in
which the bedrock is likely to be extensively concealed.
The Geologic Map does, however, represent the Quater-
nary deposits along the Atlantic and Gulf Coasts and in
intermontane areas in the West, where they are essen-
tial features of the bedrock pattern. Details of procedure
are discussed at several places further on (see p. 31).
The Geologic Map of the United States is not a tectonic
map. Tectonic maps classify the surface bedrock accord-
ing to its tectonic rather than its stratigraphic evolu-
tion, and they sometimes represent rocks and struc-
tures at considerable depths beneath the surface. They
also symbolize the folding and faulting to which the
rocks have been subjected and classify the faults as to
kind and origin. Again, the making of a tectonic map is
a worthy enterprise in itself with which we are not here
involved (although King has been so involved in the
past); tectonic maps of the United States and of North
America have already been published (Longwell, 1944;
Cohee, 1962; King, 1969).
Nevertheless, the bedrock patterns on a geologic map
have tectonic implications, and these should not be
slighted. Where the rocks have been folded, the folding
should be emphasized by the patterns of the formations,
and where the formations have been displaced by faults,
the faults should be represented. Some small-scale
geologic maps have omitted faults entirely; others have
shown them only where they offset a map unit. On the
present map, faults are shown not only to explain offsets
of the map units, but for their own sake, to illustrate the
structural grain of the region (see p. 28).
The Geologic Map of the United States is not con-
structed according to any particular tectonic principle
or theory--the permanence of continents, the oceaniza-
tion of continental material, continental accretion, con-
tinental displacement, plate tectonics, or the like. If
such theories have a place on maps, it is on tectonic
rather than geologic maps. A geologic map should pre-
sent a reasonably factual statement of the bedrock that
actually exists on the continent. It contains the data on
which a theoretician can build, if he chooses, and hope-
fully it provides constraints for the more exuberant
manifestations of theoretical geology.
The Geologic Map of the United States represents
only the geology of the continental territory of the Un-
ited States; the geology of the continental territory of
Canada and Mexico within the limits of the geographic
base is not represented. National geologic maps of
Canada and Mexico have been published (Geological
Survey of Canada, 1969; Sanchez Mejorada and Lopez
Ramos, 1968). For our own edification, we have plotted
on our copy of the United States Map the geology of
Canada and Mexico within the limits of the base, as
shown on the national maps of those countries. The
results are interesting, and the general fit across the
international boundaries is satisfactory, but there are
problems in detail of classification and unification that
it would be presumptuous for us to attempt to resolve.
Finally, the map does not represent the offshore geol-
ogy on the continental shelves and continental slopes.
Geologic maps of variable quality have been made of
parts of the offshore areas by marine geologists
(see footnote 2), but the geology of other parts is still
imperfectly known; accurate representation of all the offshore
areas of the United States is still a project for the future.
On the Geologic Map we have, however, represented the posi-
tions of the continental shelves and slopes by means of
the first 200-metre contour, and of 500-metre contours
thereafter, and with this guidance the user can, if he
wishes, mark whatever additional data meet his fancy.
The sources from which the contours were compiled
have been listed earlier (see p. 18 and [FIG_7]).
Footnote 2. See, for example, the geologic map of the sea bottom in the
North Atlantic and Gulf of Mexico adjacent to North America by Emery and
Uchupi (1972, fig. 87)
CLASSIFICATION OF THE ROCK UNITS
The general plan of classification of the rock units on
the Geologic Map of the United States is illustrated by
Figure 8 [FIG_8ab][FIG_8c].--Geologic maps of the Sandia Mountains, N.M.,
to illustrate the process of generalizing data for the Geologic Map of the
United States. A, Representation of the area on the primary source, the
Geologic Map of New Mexico of 1965; original scale 1:500,000. B, The
area when generalized, somewhat revised, and replotted on a scale of
1:1,000,000. C, The area as shown on the Geologic Map of the
United States, a further generalization from B; original scale
1:2,500,000. The representation in C appears crude by comparison
with A and B, but contains the maximum detail possible for
the map legend. The legend of the present map differs
from that of the previous map of 1932 in that all items
are combined into a single tabulation, rather than being
broken up into separate tabulations for each of the
geologic provinces. This change is now possible because
of the progress that has been made during the interven-
ing 40 years in correlation and coordination of the geol-
ogy of the country.
On the legend, the Phanerozoic rock units are
classified according to both age and kind. (The Precam-
brian rocks are treated in a similar manner so far as
possible, but they have special problems and will be
treated in a later report.) Rocks of approximately the
same age are shown at the same horizontal level in the
legend--for example, Lower Cretaceous strata and
Lower Cretaceous granitic rocks. Successive vertical
columns show different kinds of rocks. Classification
begins in the first column with what might be consi-
dered as the "normal stratified sequence," largely
marine and obeying the classic laws of superposition,
and in succeeding columns proceeds to various group-
ings of the units, then to other facies of similar age such
as continental and eugeosynclinal, to contemporaneous
volcanic and plutonic rocks, and finally to the metamor-
phic equivalents of the others.
The classification of the rock units is, if possible,
time-stratigraphic--that is, units which are of approx-
imately the same geologic ages at all places, such as
systems, series, and stages. Rock-stratigraphic units,
which may be of different ages from place to place, are
used only where they illustrate some special geologic
feature, or where the age classification is uncertain.
Unlike the legend for the Geologic Map of 1932, very
few formations and other specific stratigraphic units
are mentioned; discussion of these will be taken up in
The first column of the normal stratified sequence
lists the smaller subdivisions that are used on the map,
commonly series or groups within the systems. Ordinar-
ily, these can be shown on a map of this scale only in
regions of simple geology, where the systems occupy
wide outcrop bands. Places where such subdivisions can
be represented differ from one system to another, hence
the first column does not represent a sequence that
occurs in a single region. In general, the Paleozoic sys-
tems can be divided in most detail in the Eastern In-
terior Region, the Permian in the Western Interior, the
Cretaceous in the Western Interior and the Atlantic and
Gulf Coastal Plains, and the Tertiary in the Coastal
Plains. In a few places, the rocks of the time-
stratigraphic units dip so gently, or are so thick, that
they occupy areas too broad to express the geologic
features adequately, and smaller subdivisions are de-
sirable. The Lower Ordovician of the Ozark Plateau,
and the Montana Group in the northern Montana plains
are thus further divided into units O1a and b, and uK3a
and b, respectively.
Most of the geologic systems that form wide outcrop
bands can be divided on the map into three or four
comprehensive time-stratigraphic units, but the situa-
tion is less satisfactory in the Permian. The Permian
dips gently and forms wide outcrops in the Midconti-
nent Region, New Mexico, and northern Arizona. The
Permian forms smaller, less continuous areas in west-
ern Texas, but the rocks here are of fossiliferous marine
facies and are the basis for the standard subdivision of
the system. In each of these areas the Permian can be
subdivided in some detail. Especially impressive is the
long belt of outcrop in the Midcontinent Region, from
north-central Texas to Nebraska, where six subdivi-
sions can be traced, to a large extent on continuity of
outcrops. Nevertheless, the obvious subdivisions in
each area are not necessarily correlative, and their cor-
relation is in part controversial. In the Permian, unlike
other systems, recourse therefore had to be made to
"operational units," which are illustrated in a diagram
in the lower part of the legend. Permian stratigraphic
problems will be treated at greater length in a later
In the remainder of the United States, the geologic
systems must be shown as single map units, or several
systems must be combined, as shown in the second and
third columns of the legend. Map units that combine the
systems into more comprehensive groupings are both a
necessity and a plague to the compiler. In strongly de-
formed regions, where the strata are turned up steeply,
outcrop bands of even the major units become very nar-
row, and the niceties of stratigraphic differentiation,
appropriate for areas of simpler geology, are out of the
In the Eastern United States, we therefore resort to
hybrids--DS for Devonian and Silurian, OC for Ordovi-
cian and Cambrian, and the like. This means either that
the two systems form outcrop bands too narrow to be
separated successfully on a map of this scale, or else that
the two systems form a homogeneous body of rocks. In
making our compilations we have discovered that some
geologists have used the hybrids in another sense--DS
for Devonian or Silurian when they are not certain
which. Where possible, we have avoided this second
meaning and have made arbitrary decisions; if the
weight of evidence is more toward a Devonian than a
Silurian age, the unit is mapped as Devonian; if we are
in error, the error can be corrected later.
In the Cordilleran region of the Western United
States, even this hybridization is insufficient, and we
have resorted to the more general groupings of lPz, uPz,
and lMz, for lower Paleozoic (Cambrian to Devonian),
upper Paleozoic (Mississippian to Permian), and lower
Mesozoic (Triassic and Jurassic), respectively. This
usage will make stratigraphers and other precisionists
unhappy; it will fail to reveal to them, for example, the
nearly complete absence of the Silurian in most of the
Rocky Mountains, or the Triassic in the Sierra Nevada.
The alternative would have been to resort to complex
letter combinations, varying from one part of the map to
another, such as CD (Carboniferous and Devonian),
DSO (Devonian, Silurian, and Ordovician) and DC (De-
vonian, Silurian, Ordovician, and Cambrian) used on
the Geologic Map of North America of 1965 (Goddard,
1965)--each requiring a separate color on the map and
box in the legend.
Within the Paleozoic areas of the West, the Cambrian
and Permian at the base and top of the sequence occupy
significantly large areas in a few places, and are of
interest both stratigraphically and structurally. These
large areas are separately shown; elsewhere the two
systems are merged with the lower and upper Paleozoic.
Following the normal stratigraphic sequence are col-
umns for various facies. In the Tertiary deposits of the
West it is important to distinguish between marine and
continental deposits--the marine Tertiary along the
Pacific and Gulf Coasts, and the continental Tertiary of
the interior, which forms wide areas in the Great Plains
and the intermontane basins of the Rocky Mountains.
Problems multiply in the pre-Tertiary rocks, and con-
sistent separation of continental deposits becomes im-
possible. How should one classify coal measures, red
beds and evaporites, or sheets of fossil sand dunes, all of
which form broad units in normal stratified sequences,
which are continental in a sense, yet have at least some
tenuous marine connections? In general, these are not
shown as continental deposits on the map. In the pre-
Tertiary rocks, only the more obvious continental de-
posits are so indicated--Cretaceous adjoining orogenic
areas in the Rocky Mountains, Jurassic in the Northern
Interior, Permian near the Wichita Mountain axis in
Oklahoma, and Devonian in the Northern Ap-
Another facies that is separated comprises the
eugeosynclinal deposits. Modern tectonic studies indi-
cate that "eugeosynclinal" is a broad generic term that
embraces many specific kinds of rocks formed in differ-
ent environments--marginal seas, island arcs, deep-sea
trenches, and ocean floors. Be that as it may, the
eugeosynclinal suite embraces rocks markedly differ-
ent from the usual marine and continental deposits of
the interior of the continent--immature clastic sedi-
ments, cherts, and large volumes of volcanics and vol-
caniclastic sediments. While the generic characters are
plain, separation into specific varieties is likely to be
subjective and would, further, unduly clutter represen-
tation on the scale of the Geologic Map of the United
Eugeosynclinal deposits are represented in the
coastward parts of the Appalachians (where they are of
lower Paleozoic age), and the Cordillera (where they are
of Paleozoic and Mesozoic ages). In addition, eugeosyn-
clinal deposits of Tertiary age, very much like those of
the earlier ages, occur in the Olympic Peninsula of
northwestern Washington and are separately mapped.
Differentiation of rocks of eugeosynclinal facies em-
phasizes important structural features in the United
States, as where they have been thrust for many miles
over normal marine carbonate rocks of similar age in
the Northern Appalachians and the Great Basin.
Volcanic rocks likewise form stratified or quasi-
stratified sequences, which are equivalent to, or merge
laterally into the stratified sedimentary sequences.
Those of Cenozoic age occur primarily in the Cordille-
ran region of the Western States, where they are areally
extensive and offer the greatest opportunities for
classification and subdivision. On the present map, we
have intentionally avoided use of the units Tv and QPv
of the 1932 map, for undifferentiated volcanic rocks,
believing that the data are now sufficient, or nearly so,
to permit a meaningful regional subdivision. Basis for
classification is primarily by age (based on fossils and
radiometric data), but felsic or siliceous varieties are
differentiated where data are available; in addition,
several other compositional varieties are shown in the
Pacific Northwest. Details of classification of the
Cenozoic volcanic rocks will be considered in later
In the pre-Tertiary systems, volcanic rocks are dis-
tinguished in few places. They unquestionably form
large volumes of the eugeosynclinal deposits, but as
these are in part volcanic by definition, their volcanic
components can generally be surmised. In the lower
Paleozoic eugeosynclinal deposits of the Appalachians,
however, volcanic rocks form well-marked entities, the
areally more extensive of which are separately mapped.
Among the plutonic rocks, granitic varieties are the
most extensive and the most amenable to classification
by age, mainly on the basis of radiometric data but
partly on their geologic relations to the country rocks.
Mafic varieties are less extensive and are not sub-
divided in detail. The ultramafic rocks are a class by
themselves and are not designated by age; large parts of
them, at least, are fragments of mantle material of
enigmatic age which have arrived at their present posi-
tions by tectonic rather than magmatic processes.
Metamorphic rocks are indicated primarily by over-
prints on the parent rock units, except in parts of the
Piedmont province of the Appalachians and in the Cas-
cade Range of the Pacific Northwest, where the ages of
the parent rocks are as yet undetermined; such rocks
are designated as "metamorphic complexes." The
metamorphic overprint is not used in the Precambrian
rocks; the designation of certain units as "orthogneiss"
or "paragneiss" seems sufficient to indicate their
Rocks shown as "metamorphic" are primarily those of
amphibolite grade or higher, that is, with garnet, kya-
nite, sillimanite, and other diagnostic minerals. Rocks
that have been altered to greenschist grade, with chlo-
rite, biotite, and similar diagnostic minerals, are not
represented as metamorphic. Near the West Coast, in
California and Oregon, upper Mesozoic eugeosynclinal
rocks (uMze, Ke) have been subjected to high-pressure
low-temperature metamorphism, producing various
blueschist minerals. In this domain regionally
metamorphosed rocks containing glaucophane, lawso-
nite, and pumpellyite are shown as metamorphic; lower
grade rocks with laumontite and similar minerals are
not. In a few places on the map the metamorphic over-
print is used to express geologically significant
metamorphic rocks or metamorphic contrasts, without
regard to mineral content; thus some of the rocks of the
Olympic Mountains, Wash., are shown as metamorphic,
even though they are low grade mineralogically.
SYMBOLIZATION OF ROCK UNITS
On the Geologic Map itself, the rock units are dif-
ferentiated by colors, patterns, and letter-number sym-
bols. Of these, the colors present the greatest problems
and hence will be dealt with in most detail.
Colors on a geologic map have two facets--geological
philosophy and the technology of lithography and print-
ing. The latter need not concern us greatly here, as it is a
matter of the techniques of producing colored maps;
these change from generation to generation, although
the general results are much the same. The geological
philosophy is more fundamental, and one upon which
there are still significant differences of opinion and
One can, if one wishes, produce an empirical rep-
resentation, in which the choice of colors on the map has
no general meaning--usually for the purpose of creat-
ing contrasts between map units, thereby enhancing
legibility. An excellent example is the Geologic Map of
Pennsylvania (Gray and others, 1960), in which the
colors are used unsystematically, yet eloquently por-
tray the structure and stratigraphy of the State. This
method is best adapted to large-scale maps, or regional
maps of restricted areas, and would be inappropriate for
the Geologic Map of the United States.
The best alternative is to match the orderly sequence
of rock units from oldest to youngest with an orderly
sequence of prismatic colors (consult the Munsell color
notation system, which has been adopted by the Ameri-
can Standards Association). As stated by Willis (1912,
Let it be agreed that the sequence red, purple, violet, blue,
green, and yellow shall be adopted to represent the succession
of formations, groups, or series of sedimentary rocks from older
to younger and let the order of colors be invariable according
to the principle stated above, no matter what part or how much
of the geologic column is represented. Then red will always
represent something older than that which is shown in purple,
or violet, or blue, etc. Blue will always be older than that shown
in green or yellow. In looking at any geologic map thus colored
the student would at once know which were the older and which
were the younger sedimentary rocks. The essential features of the
sequence and structure would be immediately obvious.
Most systems of coloring geologic maps use this general
principle, although with greater or lesser departures
from it, as we shall see.
Efforts to achieve a systematic scheme for coloring
geologic maps are nearly a century old, and their his-
tory is pertinent. By the 1870's, the proliferation of
geological investigations in both Europe and North
America made obvious the need to systematize
results--in stratigraphy, mineralogy, paleontology,
and the making of geologic maps. This led to the conven-
ing of the First International Geological Congress in
Paris in 1878, the results of which were inconclusive.
Decisions were therefore deferred until the Second
Congress (Bologna) in 1881 and the Third Congress
(Berlin) in 1885 (see footnote 3). Only the results
that pertain to the making of geologic maps need concern
us here; many of the recommendations made on the other
subjects have only historical interest.
Footnote 3. The results have been published in the respective
reports of the first three congresses, in which the official
language was French. For the American reader, they were usefully
summarized by the secretary of the American Committee, Persifor
Frazer (1888). In addition, G. K. Gilbert (1887) presented a
lengthy critique of the results of the Third Congress.
The prime need at the time was a comprehensive
scheme of symbolization for use on a Geologic Map of
Europe, then being compiled by an international com-
mittee. Although some geologists protested that the
results were provisional and experimental and applied
only to the European project (Frazer, 1888, p. 95), there
were misgivings by others at the time that they would
crystallize into a permanent general usage (Gilbert,
1887, p. 432)--a foreboding that has been amply
justified by subsequent events. Immediately thereafter,
the color scheme adopted by the 1881 and 1885 Con-
gresses was used by C. H. Hitchcock (1887, p. 466-467)
for coloring his Geologic Map of the United States (see p.
7), and today it is commonly referred to as the "Inter-
national system" by European geologists, who have
urged its adoption on a worldwide basis.
Meanwhile, however, J. W. Powell was appointed
second Director of the U.S. Geological Survey in March
1881, and in his first official report, written a few
months later, announced a scheme of stratigraphic
nomenclature, map coloring, and patterns to be used
thenceforth in Survey publications (Powell, 1882, p.
xliii-liii) even though: "On the 26th of September next
(1881) a congress of geologists of the world will assemble
at Bologna, Italy, to confer on this subject. It is unfortu-
nate that advantage cannot be taken of the delibera-
tions of so great a body of savants in the publication of
these monographs, but the exigencies of the work will
not permit of longer delay even for so important a pur-
pose" (p. xlii). Viewed from the perspective of nearly a
century the justification for this precipitate action
seems specious; it was probably dictated by immediate
political problems in Washington (see footnote 4). Somewhat later he
presented the methods used by the U.S. Geological Sur-
vey to an international audience in a paper at the Berlin
Congress (Powell, 1888, especially p. 236-239), deli-
vered in his behalf by W J McGee.
Footnote 4. Stegner (1954, p. 271-272) presents some interesting
speculations on the circumstances.
The scheme proposed by Powell has laid the ground-
work for usage in publications of the U.S. Geological
Survey to the present time. Detailed specifications for
usage in these publications were promulgated in 1890,
after areas of diverse geology in many parts of the coun-
try had been sampled by mapping, and after conferences
with 18 of the leading Survey geologists of the time
(Powell, 1890, p. 56-79); they differ in detail from the
original proposal of 1881, but the broader features re-
main the same. Thus, Powell's original map colors, with
subsequent elaborations, have become the United
States, or "American color system."
The principal differences between the "American"
and the "International" color systems are in the
stratified sedimentary rocks; the intrusive and volcanic
rocks in both systems are shown in more brilliant tints,
with a preference for the reds and oranges. The two
systems are compared in table 1; the original proposal
for each is followed by samples of subsequent usage,
including that on the present Geologic Map of the Un-
The reasons for the differences between the two sys-
tems are ably explained by Willis (1912, p. 24-26):
The European international color scheme embodies the results of
prolonged consideration by the international committee who were
charged by the Geological Congress with the duty of preparing the
map of Europe. In it can be recognized some elements of the French
usage, particularly in the colors employed for the Mesozoic and Ter-
tiary terranes. German influence appears in the selection of tones for
the Paleozoic terranes, and the familiar association of gray with
Carboniferous and of pink with the ancient crystalline schists is an
obvious result of general practice. So also is the use of strong
brilliant colors for the igneous rocks. The writer is not definitely
informed regarding the discussion of principles through which the result
was reached, but a study of the color schemes in the light of what is
published concerning the controlling principles, it would seem that
the committee recognized (l) established usage, (2) the order of pris-
matic colors from purple through blue and green to yellow for that
portion of the scheme relating to the Triassic and post-Triassic ter-
ranes, and (3) the arbitrary principle that Mesozoic terranes should be
distinguished from Paleozoic by a very decided contrast of light and
shade, the Paleozoic terranes being indicated by dark colors.
The European color scheme is exceedingly well adapted to delineate
the geology of Europe and would apply very well to that portion of
western North America in which the Mesozoic and Tertiary forma-
tions occupy large areas in contrast to the Paleozoic terranes, as they
do in Europe also. The color scheme thus commends itself through the
beautiful appearance of the map. It must not be forgotten, however,
that Europe represents a special form of geologic structure. The conti-
nent is made up of extensive areas of Mesozoic and Tertiary strata
surrounding relatively small exposures of Paleozoic terranes. This
arrangement of younger strata about older nuclei is, from the stand-
point of the cartographer, the most important feature which the con-
tinent presents. The committee with good reason sought to emphasize
the fact and through that emphasis the map of Europe gains in
expression and educational value. The greater part of the map is
easily legible, being covered only by the light colors which are used
for the Mesozoic and Tertiary, and the difficulties which arise in
attempting to read the geology of the minor Paleozoic areas are not
forced upon the attention.
But the international scheme is unfitted to lands in which the
Paleozoic terranes predominate and are minutely subdivided, for the
density of the colors selected for the Paleozoic would produce a map
that would offend good taste and be illegible. Moreover, inasmuch as
the range of prismatic colors from purple, blue, and green to yellow is
preempted in the European color scheme for Mesozoic and Tertiary
terranes and the reds assigned to the ancient crystalline and eruptive
rocks, the choice of colors remaining available for the Paleozoic is
much too limited for satisfactory discriminations. This is at once
evident on an examination of the Paleozoic areas as represented on
the international map--such, for instance, as the coal fields of Bel-
gium and France, or the peninsula of Brittany, or Wales and Scotland.
Although the distinctions are limited to a few great systems they are
recognizable only on close inspection and the areas are indistinguish-
able from one another at a little distance. A geologic map of eastern
North America printed in these dark colors with so little difference of
hue or shade would fail to present adequately the great Appalachian
zone as distinguished from the broad plateaus of the coal measures
and the domelike uplifts of the Cincinnati axis. In the Precambrian
also the number of formations recognized in North America is greatly
in excess of those distinguished in Europe, and the simplicity of the
European scheme renders it insufficient to delineate the geology of the
Lake Superior region and the Canadian Shield.
The validity of Willis' evaluation is substantiated by
the results of attempts to apply the so-called "Interna-
tional system" to continents where the gross geologic
structure and surface distribution of the geologic sys-
tems differ significantly from those of Europe. The in-
adequacy of the "International system" for Australia is
lamentably evident on the otherwise beautifully
printed sheets for this part of the Geological Map of the
World (Bureau of Mineral Resources, Geology, and
TABLE 1. Comparison between "American" and "International" systems of
coloring stratified rocks on maps
Geophysics, 1965). The Tectonic Map of the country
(Tectonic Map Committee, Geological Society of Au-
stralia, 1971) and recent maps of individual states use
an approximation of the "American system" and pro-
duce a much clearer picture of the regional geology. It is
of interest to compare the systems of Europe and the
United States with that adopted on the Geological Map
of Canada (Geological Survey of Canada, 1969); as in
the "American system" it follows a prismatic scale, but
the blue colors are extended downward to the base of the
Paleozoic, reserving the red, orange, and brown colors
for the Precambrian, in which rocks of many kinds and
ages must be differentiated.
The colors used on the present Geologic Map of the
United States conform as far as possible to the tradi-
tional "American system," in which the prismatic scale
of colors embraces the whole geological sequence, from
earliest Precambrian into the Quaternary. Some depar-
tures are necessary, it is true, due to modern methods of
lithography, and to obtain greater emphasis of some
units. (Similar freedom has been exercised within the
so-called "International system," as is evident in the
last two columns of table 1. In order to clarify the
growing complexity of the Precambrian sequence, the
rocks of division X are separated from the prevailing
reds and browns of the other divisions by the use of tints
of bluish gray; and the Oligocene and Miocene Series of
the Tertiary are distinguished from the prevailing yel-
lows of the others by the use of flesh and pale-brown
Traditionally, on geologic maps published by the U.S.
Geological Survey, the meaning of colors has been en-
hanced by the use of patterns, as explained in the text
that accompanied all the folios of the Geologic Atlas:
"Patterns composed of parallel straight lines are used to
represent sedimentary formations deposited in the sea,
in lakes, or in other bodies of standing water. Patterns
of dots and circles represent alluvial, glacial, and eolian
formations. Patterns of triangles and rhombs are used
for igneous formations. Metamorphic rocks of unknown
origin are represented by short dashes irregularly
placed; if the rock is schist the dashes may be arranged
in wavy lines parallel to the structure planes." Use of
patterns was more feasible with the older methods of
lithography than the methods used at present, in which
it is more practical to use flat tints; but they can still be
achieved by overprints on the flat colors--as has been
done on recent maps of the U.S. Geological Survey and
on maps published in the Soviet Union and elsewhere.
One need only to study a map without patterns to be-
come painfully aware of their mnemonic value; not even
the use of vivid, contrasting colors for plutonic rocks and
lavas (as on the Geologic Map of France, 1968) conveys
the distinctions as clearly and immediately as do pat-
On the Geologic Map of the United States, over-
printed patterns are used to indicate plutonic rocks,
metamorphic rocks, and some of the volcanic rocks. For
the granitic class of plutonic rocks we have used the
"short dashes irregularly placed" (there is no better
descriptive term for this excellent and expressive pat-
tern); it implies massive crystalline rocks, so that its
former use in the folios for metamorphic rocks has be-
come inappropriate. The pattern is superposed on a
color expressing the age of the granitic pluton (which
can now be determined from radiometric data). For
metamorphic rocks a dense halftone overprint is substi-
tuted; the "random dashes" of earlier maps were too
weak to differentiate these rocks clearly. For the vol-
canic rocks we use various v-patterns, a simplified form
of the "rhombs and triangles" of the folios.
It is most desirable that colors on a map be identified
by letter/number symbols to assist the user in compar-
ing the map with its legend. The handicap of a colored
map without symbols is at once apparent to the user of
the otherwise excellent sheets of the 1:200,000 Geologic
Map of Switzerland, in whose complex parts there are
many small patches and bands of color that he must
endeavor to match with one of an assortment of similar
colors in the legend.
The simplest form of symbolization is by numbers,
which are appropriate where there are only a few units,
but confusing when they number 50 or more, as on some
Canadian maps. Being entirely noncommittal, num-
bers have no mnemonic value--an advantage or a dis-
advantage, depending on the circumstances.
Much more common are single or multiple letters, or
letters combined with numbers, several systems of which
have been used--no one better than the other. In the
specifications for the Geologic Map of Europe adopted by
the International Geological Congress, geologic ages of
strata were expressed by roman lowercase letters,
modified by suffixed numbers, and different kinds of
eruptive rocks were shown by Greek letters. On many
other geologic maps, including those of the U.S. Geolog-
ical Survey, general age is expressed by capital roman
letters representing the geological systems, modified by
suffixed lowercase letters. The symbols used on the
Geologic Map of the United States resemble those of the
latter system; variants are introduced by prefixing the
initials l, m, and u (for "lower," "middle," and "upper"),
to avoid complicating the suffix, and by use of suffixed
numerals rather than letters for the smaller age divi-
sions, reserving lowercase letters for descriptive
modifiers, such as c for "continental" and v for "vol-
canic." Throughout, we have avoided long strings of
modifying suffixed letters, which often become annoy-
ing acronyms. The only exceptions are the symbols for
Tertiary eugeosynclinal deposits of the Olympic Penin-
sula, Wash.--Tmoe and Toee, for "Tertiary Miocene-
Oligocene eugeosynclinal" and "Tertiary Oligocene-
Eocene eugeosynclinal." Not all the units shown on the
Geologic Map require qualification by a lowercase
suffixed letter. Many of them represent a whole geologic
system (or several systems); for these, the capital letters
alone are sufficient.
REPRESENTATION OF FAULTS
As indicated earlier (p. 21), faults are shown on the
Geologic Map of the United States, not only to explain
offsets of map units, but for their own sake, to express
the structural grain of the area. The density of faults
represented on the geologic map thus equals that which
would appear on a tectonic map of the country, but they
are marked simply as faults, not as low-angle or high-
angle thrust faults, normal faults, or strike-slip faults;
for this information the user should consult the appro-
priate tectonic map.
By the method adopted, faults are shown not only at
contacts between map units, but within map units.
Some of these are major faults with large displace-
ments. In Arkansas, the great frontal thrusts of the
Ouachita Mountains all lie within the combined
Atokan and Morrowan Series (Pennsylvanian1), which is here more
than 4 miles thick; the lower part of the unit is displaced
against the upper, as would be evident on a more de-
tailed map. Other faults within map units are them-
selves minor, but are components of major structures;
those lying in the volcanic units of eastern Oregon are
merely a sampling of the dense swarms that appear on
maps of larger scale, which are arranged in regional
sets of several directions.
In the Basin and Range province of the Western
United States we have made a special effort to represent
range-front faults where geomorphic evidence (steep
mountain faces, even base lines, and the like) requires
their existence; more timid compilers often fail to show
them, thereby creating the illusion of an unfaulted ter-
rane. Commonly, the range-front fault lies a short
distance out from the foot of the range beneath the al-
luvium; on a large-scale map it would be shown as a
dotted line parallel to and closely adjacent to the bed-
rock contact of the range. On the small scale of the
present Geologic Map, only the fault itself is shown, and
the bedrock contact is not.
Although the faults on the geologic map are
unclassified, their patterns suggest something of their
geometry. For example, in the Taconic region of eastern
New York State, an array of sinuous fault traces (many
closing on themselves) expresses flat or gently dipping
thrusts and contrasts strongly with the straight or an-
gularly bent traces of the high-angle faults of the
Adirondack uplift and those on the borders of the belts
of Triassic rocks.
Low-angle thrust faults geometrically like those in
the Taconic area of eastern New York State are compo-
nents of the internal structure of the ranges in the Great
Basin section of the Basin and Range province [FIG_9].
They are older than the range-front faults just men-
tioned, which greatly disrupt them. The major low-
angle thrusts of the Great Basin section are recogniza-
ble from range to range by distinctive rocks on their
upper and lower plates, but their original continuity is
difficult to represent on the geologic map because of the
confusing array of other rocks and structures; dotted
lines are used in a few places to suggest the obvious
The regional extent of these faults is indicated on the
accompanying figure [FIG_9], which shows the inferred traces of
the frontal thrusts of the Sevier orogenic belt in Utah (of
mid-Cretaceous age), of the Roberts thrust in north-
central Nevada (of late Devonian-early Mississippian
age), and of the Golconda thrust a little farther west (of
late Permian-early Triassic age). On large-scale maps
the experienced eye could detect each of these by its
characteristic "trademark," but these "trademarks" are
necessarily blurred on the much generalized, small-
scale Geologic Map of the United States. Nevertheless,
even on this map the different segments of the Roberts
thrust are apparent from the juxtaposition of
FIGURE 9 [FIG_9].--Map of the Great Basin in Nevada and Utah, showing
regional extent of major low-angle thrust faults that are represented
on the Geologic Map of the United States as exposed fragments in
the mountain areas. The thrusts involve only the Paleozoic and
Mesozoic strata, whereas the mountain areas also include plutonic
and stratified rocks younger than the thrusting.
eugeosynclinal lower Paleozoic rocks (lPze) and normal
lower Paleozoic rocks (lPz) on its upper and lower plates.
Explanation is needed of the nearly circular fault
traces of small to medium diameters which appear in
places on the Geologic Map [FIG_10]. They are of multi-
ple origins, some being the rims of calderas (produced by
terrestrial volcanism), others the edges of astroblemes
(produced by extraterrestrial impact). Parts of these are
shown by dashes, not to imply that they are hypotheti-
cal but to suggest that the marginal faulting around the
central structure is discontinuous. As with the other
faults, they are not further symbolized on the geologic
map. Moreover, they are shown only where they con-
spicuously affect the surface bedrock pattern. Many
more calderas and astroblemes could be represented on
a tectonic map, but they would not conspicuously affect
surface geology; such calderas are old, worn down, and
largely buried, and the astroblemes are little structures
within single map units. We have made one exception of
the great caldera rim in Yellowstone National Park,
nearly 40 mi (65 km) in diameter, even though it is
extensively concealed by ash-flow tuffs and rhyolite
FIGURE 10 [FIG_10].--Circular faults shown on the Geologic Map of the
United States. A and B are associated with calderas, C and
D with astroblemes. A, Yellowstone and Island Park calderas
northwestern Wyoming and adjacent Montana. B, Calderas in
San Juan Mountains, Colorado. C, Monson structure, central
Iowa. D, Wells Creek Basin, west Tennessee. Contacts are
the same as on the Geologic Map, but units are grouped in the
flows resulting from the eruption; it is one of the major
structural features of the United States and should not
REPRESENTATION OF CONTACTS
Throughout the Geologic Map of the United States,
contacts between map units (where not faulted) are
represented by fine solid lines except where one set of
map units merges with another along the strike; here
the colors of the two are juxtaposed without a contact
line. A conspicuous example is in northwestern Iowa
and south-western Minnesota, where subdivisions of
the Upper Cretaceous that are separately shown to the
west give place eastward to undifferentiated Upper
Cretaceous. Along the outcrop belts in the folded Ap-
palachians, subdivisions of the Paleozoic systems simi-
larly give place along the strike to undivided systems,
but these features are of smaller areal extent, and are
only apparent on close inspection of the map.
A "state-line unconformity" occurs between North
and South Dakota, in an area of heavy drift cover where
the contact between the Colorado and Montana Groups
of the Upper Cretaceous (uK2 and uK3) fails to match by
several counties on the bedrock maps of the respective
States, the contact has been reconciled by sketching
across the state line. Other "state--line unconformities"
(discrepancies between map units as represented in ad-
joining States) abounded on our initial compilations but
were resolved upon inquiry.
Subdivisions of the Eocene Series in the Mississippi
Embayment of western Tennessee and the Atlantic
Coastal Plain of southwest Georgia are inaccurately
located; in Tennessee the contact between Te2 and Te3 is
concealed by a blanket of Pleistocene loess, and in Geor-
gia by residuum. The location of the contacts between
the Eocene and the Oligocene (To) and the Oligocene
and the Miocene (Tm) in Georgia are also in doubt.
Drilling beneath these blankets is insufficient to clarify
the actual bedrock pattern, and for want of better in-
formation we have projected the contacts hypothetically
The southwestern part of the Blue Ridge province of
northern Georgia was inadequately mapped at the
time of compilation, but a hypothetical contact between
supracrustal rocks (Z) and basement rocks (Ym) was
mapped. For a more accurate representation, see the
new Geologic Map of Georgia (in press, 1974).
Dotted lines, expressing contacts buried by younger
deposits, are used sparingly on the Geologic Map, for the
most part to indicate connections between closely adja-
cent areas of outcrop but also in southwestern Min-
nesota and in the Mississippi Embayment.
Those in Minnesota are boundaries between Precam-
brian units beneath a blanket of Upper Cretaceous
strata and glacial drift, as shown on the Bedrock
Geologic Map of Minnesota (Sims, 1970), and are sup-
ported by a variety of drilling and geophysical data.
Those in the Mississippi Embayment are contacts
between various series of the Tertiary and subdivisions
within the Eocene Series buried beneath the Quater-
nary deposits of the alluvial valley of the Mississippi
River. The Quaternary deposits (Pleistocene and
Holocene) are several hundred feet thick and are an
essential feature of the bedrock pattern. The Tertiary
units are exposed on each side of the alluvial valley and
are connected beneath it in subcrop, where they are
represented by dotted lines. These lines explain buried
features of interest, especially the large outliers of
Jackson Group (Te3) north of the normal belt of outcrop,
where they are preserved in the downwarp of the Desha
basin. The extent of the Tertiary units in subcrop is well
known from many drill data, which were first assem-
bled by Fisk (1944, pl. 10); representation on the
Geologic Map includes some later refinements.
In the areas on the Geologic Map where extensive
subcrop is represented by dotted contacts, it is clarified
by letter symbols of the buried units in parentheses.
The present Geologic Map of the United States, like
the map of 1932, is intended to represent bedrock rather
than surficial deposits. The map shows principally the
distribution of the Tertiary and older rocks, and the
surficial deposits of the country are largely of Quater-
nary age. Quaternary deposits are shown on the map
where they are thick enough, or tectonically significant
enough, to be an essential part of the bedrock pattern. In
some parts of the country, bedrock is represented even
where the cover of surficial deposits is extensive and
outcrops are sparse; here, outcrops must be sup-
plemented by drill and geophysical data to produce a
subcrop map. The most extensive area of such surficial
cover is in the part of the Northern Interior States
subjected to continental glaciations during Pleistocene
time, but smaller areas occur elsewhere outside the
NORTHERN INTERIOR STATES
In the Northern Interior States the extent of the
surficial cover is suggested on the geologic map by lines
showing the limits of the latest (Wisconsin) glaciations
and of the older glaciations. Concealment of the bedrock
is greatest in the area of the Wisconsin glaciations, but
it is nearly equalled in a few parts of the area of the older
The extent of the concealment is illustrated by the
accompanying maps of eastern South Dakota [FIG_11].
West of the Missouri River there is little surficial cover,
and the bedrock is mapped from outcrops. East of the
FIGURE 11 [FIG_11].--Maps of eastern South Dakota, to illustrate problems
of representing bedrock geology in areas with extensive cover of surficial
deposits. A, Surficial, or Quaternary glacial deposits, generalized from
Flint (1959). B, Bedrock geology as shown on Geologic Map of the United
States. Outcrops of bedrock east of Missouri River are from Geologic Map
of South Dakota of 1953; contacts elsewhere, shown by dotted lines, are
those shown on the Geologic Map of the United States and are subcrop
representations based on subsurface data.
river the cover of Wisconsin glacial deposits is nearly
complete, including massive terminal moraines, and
intervening areas of ground moraine, outwash, and
lacustrine deposits. Bedrock emerges only in a few
places along the streams, with two or three outcrops to a
county at most, and in some counties none at all.
Most of the glaciated region in the Northern Interior
States is a terrane of gently dipping Paleozoic strata
that had been dissected into a dendritic pattern by
stream erosion prior to the glaciations. The contacts
between the map units show the crenulations charac-
teristic of such dissection, including long narrow projec-
tions of older units into areas of younger, which express
preglacial stream valleys, now filled and obliterated.
Especially striking examples of these features occur
along the Ordovician-Silurian contact in western Ohio
and eastern Indiana. Segments of preglacial stream
valleys have been known in this region from water-well
drilling since the turn of the century, but only in the last
few decades has it been recognized that they are all
parts of a single major river system, quite different from
the present major Ohio River system (Horberg, 1945, p.
356-359; Janssen, 1952). The master stream was the
Teays River, named for a now-empty valley near
Charleston, W. Va. (Tight, 1903, p. 50). Its headwaters
were the present New and Kanawha Rivers, which
drain from the Appalachian Highlands. Northwest of
the present Ohio River, the valley of the Teays passes
under glacial deposits and has no surface expression,
but it can be traced in subcrop across Ohio and Indiana
(where it and its tributaries produced the crenulations
in the above-noted Ordovician-Silurian contact), and
into central Illinois, where it joined the ancestral Mis-
sissippi River near the present course of the Illinois
Other preglacial valleys in northwestern Missouri
are illustrated on an inset map accompanying the
Geologic Map of Missouri (McCracken and others, 1961)
and produce crenulations in the contacts between Penn-
sylvanian map units unrelated to modern drainage.
Another crenulation, on the Precambrian-Cambrian
contact in central Wisconsin, has been shown on many
earlier geologic maps and was thought to have been
produced by the ancestral Wisconsin River; however,
modern reviews of the subcrop data indicate that this
valley, if it exists, does not penetrate the top of the
Precambrian in this manner (Dutton and Bradley,
1970, sheet 5).
In the northern two-thirds of Minnesota the prevail-
ing terrane is Precambrian rather than Paleozoic, and
in its western part the amount of surficial cover again
requires recourse to subcrop mapping. On the Geologic
Map of 1932, this part was mostly represented as
Quaternary, for want of better data. Much more infor-
mation on the bedrock is available now, from drilling
and geophysical surveys, so the patterns of Precam-
brian units can be extended westward across the State
to join the Precambrian in the valley of the Red River
FIGURE 12 [FIG_12].--Generalized geologic map of eastern Middle Western
States, to show relation of subcrop geology of preglacial river systems.
Preglacial drainage compiled from Tight (1903), Horberg (1945), and
shown on the bedrock geologic map of North Dakota
(Sims, 1970; Carlson, 1969).
The situation is complicated by the fact that in part of
northern Minnesota a thin sheet of unconsolidated Cre-
taceous deposits intervenes between the Pleistocene
and the Precambrian [FIG_13]. These deposits are the
Coleraine Formation (Sloan, 1964, p. 8-15), which has
been exposed in mine workings on the south flank of the
Mesabi Range and is known elsewhere from dril-
ling and sparse natural outcrops. Part of the formation
is marine, and its fossils indicate that it is equivalent to
the Upper Cretaceous Colorado Group (uK2) that occurs
in North and South Dakota to the west.
We believe that, for purposes of the Geologic Map of
the United States, the feature of primary interest in
northern Minnesota is the Precambrian bedrock, and
we have accordingly extended it in subcrop across most
of this part of the State. The Pleistocene deposits can be
sacrificed without regret, even though they attain
thicknesses of many hundreds of feet in places. Omis-
sion of the Cretaceous Coleraine Formation is less de-
fensible, and under other circumstances it should
perhaps be represented, yet to do so here would greatly
obscure the essential Precambrian pattern. We have
FIGURE 13 [FIG_13].--Geologic map of northern Minnesota, showing the extent
of thin Upper Cretaceous deposits (Coleraine Formation) that are
not represented on the Geologic Map of the United States. Compiled
from Sloan (1964) and Sims (1970).
therefore classified the Cretaceous with the Pleistocene
as part of the overburden on the Precambrian subcrop
but have shown its known extent in [FIG_13].
In several places outside the glaciated area of the
United States, eolian deposits of Pleistocene and
younger age cover areas so extensive that the bedrock
beneath them is represented in subcrop (see Thorp and
In northwestern Nebraska an area of about 20,000
square miles was shown as Quaternary on the Geologic
Map of 1932, on the authority of N. H. Darton and G. E.
Condra [FIG_14]. This is the Sand Hills region, whose
dunes and drifted sand, or Sand Hills Formation, lie on
the Pliocene continental deposits of the Ogallala For-
mation (Tpc), from which they were ultimately derived
(Reed and others, 1965, p. 199). Although the Nebraska
Sand Hills are a prominent geomorphic feature of the
Great Plains, they are merely surficial cover and hence
are omitted from the present Geologic Map.
East of the alluvial valley of the Mississippi River, in
Mississippi, Tennessee, and Kentucky, the Tertiary
bedrock of the uplands is mantled by loess, a windblown
dust derived from the alluvial valley, when it was in its
braided-channel phase during the late Pleistocene, and
before it entered its present meander-belt phase
(Krinitzsky and Turnbull, 1967, p. 7-9; Snowden and
Priddy, 1968, p. 129-140). The loess is as much as 100
feet (30 m) thick in the bluffs next to the alluvial valley
but thins irregularly eastward to a featheredge. On the
State geological maps the loess belt is shown as about 25
miles (40 km) wide in Mississippi and more than 50
miles (80 km) wide in Tennessee; it actually extends
east of the alluvial valley for 100 to 150 miles (160-250
km), but the remainder is thinner and less continuous
(Thorp and Smith, 1952). Although the Mississippi Val-
ley loess is appropriately shown on the State geologic
maps, it would be inappropriate on the Geologic Map of
the United States. In Tennessee it conceals the
Claiborne-Jackson contact (Te2-Te3).
In southeastern Washington and adjacent States
another loess deposit, the Palouse Formation, exten-
sively covers the basalts of the Columbia River Group
(Tmv) and was probably derived during Pleistocene
time from the front of the Cordilleran ice sheet to the
north (Richmond and others, 1965, p. 238). On the
Geologic Map of Washington (Huntting and others,
1961), much of this part of the State is mapped as
Quaternary, including not only the Palouse (Qce), but
also various units of glacial outwash and stratified drift,
so that the true bedrock pattern is not apparent. Actu-
FIGURE 14 [FIG_14].--Map of western Nebraska, showing bedrock geology
as represented on the Geologic Map of the United States, superposed
on which are the areas of Quaternary sand dunes and drifted sand
(Sand Hills Formation) as represented on the Geologic Map of the
United States of 1932 and by Thorp and Smith (1952).
ally, the Palouse Formation is a surficial cover on the
Columbia River Group in the uplands, whereas the
other Quaternary deposits occur in structural depres-
sions where they lie on older Pleistocene and on
Tertiary deposits. On the Geologic Map of the United States
we have therefore omitted the Quaternary deposits in
the uplands but have retained those in the depressions,
in the same manner as shown by Newcomb (1970).
ATLANTIC COASTAL PLAIN
In the Atlantic Coastal Plain, from South Carolina
northward to New Jersey, we have followed the usage
on the Geologic Map of 1932 and have shown the
Quaternary only in the coastal areas and represented
the inland areas as bedrock of Miocene age and older.
Actually, Pleistocene and possible Pliocene deposits
cover parts of the surface of the inland areas, in places to
such an extent that representation of the older strata
must be by subcrop mapping.
The surficial deposits are shown separately on the
Geologic Map of Maryland (Weaver and others, 1968)
and as overprints on the geologic maps of New Jersey
and Virginia (Lewis and Kmmel, 1910-12; Milici and
others, 1963); map data for the other States are less
definite [FIG_15]. The deposits have been variously in-
terpreted as between marine and continental, as to
whether they are classifiable according to altitude (that
is, whether they formed on surfaces representing differ-
ent stands of the sea during the Pleistocene), their rela-
tion to glaciation, and their relation to crustal warping;
the place for resolution of these problems should be on a
surficial geology map, rather than on the Geologic Map
of the United States.
On the source maps, the older surficial deposits are
better defined than the younger, as they form erosional
remnants and outliers on the higher divides of the coun-
try. One of them, the Brandywine Formation is pre-
served on the uplands between Chesapeake Bay and the
Potomac River in southern Maryland. Another, the
Bridgeton Formation, is extensive in southern New
Jersey, and a little farther north are smaller remnants
of the apparently older Beacon Hill Formation. All of
these are alluvial or fluviatile deposits whose ages are
speculative at best. The Brandywine may be Pliocene
(Hack, 1955, p. 25-40), as well as the Beacon Hill; the
Bridgeton may be early Pleistocene, yet it is not clearly
separable from the presumably younger Pensauken
Formation (Richards, 1965, p. 130-131). These forma-
tions resemble in origin and geographic habit the Cit-
ronelle Formation of the Gulf Coast (differentiated on
the Geologic Map as a continental deposit of Pliocene
age, Tpc), although they are not necessarily of the same
age. There is something to be said for showing the de-
posits in Maryland and New Jersey in the same manner
as the Citronelle, but to do so would obscure the already
small-scaled pattern of the bedrock outcrops, and it
would be difficult to know how far to extend them be-
cause their correlation with surficial deposits in other
parts of the Coastal Plain is uncertain; they are there-
In closing this general discussion of the Geologic Map
of the United States, a few remarks should be made
about a curious feature (or pseudofeature) apparent to
anyone who views the map from a little distance--the
"radiating strikes" or belts of outcrop which fan out in
all directions from the Arbuckle Mountains uplift in the
southern Midcontinent Region of southern Oklahoma.
The feature was observed years ago by Arthur Keith (see footnote 5) on
the basis of the general mapping available at the time;
it is much more apparent on the Geologic Maps of the
United States of 1932 and 1974.
Footnote 5. Arthur Keith, lecture at University of Texas, Austin,
while visiting professor, 1926. We have been unable to find a reference
to the subject in his publications.
The "radiating strikes" involve a number of disparate
geological elements that can be sorted out as follows
(1) Strikes of belts of Pennsylvanian and Permian
strata in the Prairie Plains homocline, across Ok-
lahoma into Kansas on the north, and into north-
central Texas on the south.
(2) Tectonic features of Paleozoic age that cross the
homocline transversely in Arkansas and Oklahoma.
East of the Arbuckle area they include the south flank of
the Ozark uplift and folds and faults in the Arkoma
basin and Ouachita Mountains. West of the Arbuckle
area they include the axes of the Anadarko basin and
the Wichita Mountains uplift.
(3) Strikes of homoclinal belts of Cretaceous rocks on
the north and west flanks of the East Texas embayment
in the Gulf Coastal Plain.
The southern Midcontinent Region is geologically
and tectonically complex, with many features of differ-
ent ages crossing each other or superposed, only parts of
which are revealed in the surface bedrock pattern;
abundant subsurface data indicate many other features
and in places quite a different history than would be
inferred from the surface geology alone. Hence, many of
the "radiating strikes" are illusory, or coincidental at
most. The only truly valid features are the radiating
strikes of the belts of Pennsylvanian and Permian
strata in the Prairie Plains homocline. Their con-
vergence toward the Arbuckle Mountains uplift indi-
cates that tilting of the strata near the uplift was more
FIGURE 15 [FIG_15].--Geologic map of the Atlantic Coastal Plain in
Maryland, Delaware, and New Jersey, showing the relation of the bedrock
units that appear on the Geologic Map of the United States to surficial
deposits of Quaternary and late Tertiary age. Compiled from
state geologic maps and from Owens (1967).
steeply westward than farther north or south--al-
though even where steepest it amounts to no more than
a few feet per mile.
Despite the questionable nature of this feature it has
recently been exploited by Burke and Dewey (1973, p.
420-421), with the aid of some subsurface data, as a
triple or quadruple rift junction in the continental plate
produced by global tectonic movements during late
Paleozoic time (styled the "Dallas junction"). The
merits of this proposal remain to be evaluated.
Figure 16 [FIG_16].--Map of the southern Midcontinent Region in Oklahoma,
Arkansas, and Texas, showing "radiating strikes" in Paleozoic and
Cretaceous rocks. Lines are generalized from contacts shown on Geologic
Map of the United States.
Anonymous, 1873, (Review of) Geological map of the United States,
compiled for the 9th Census, by C. H. Hitchcock and W. P. Blake:
Am. Jour. Sci., 3d ser., v. 6, p. 64-66.
----- 1881, (Review of) Geological map of the United States, compiled
by C. H. Hitchcock: Am. Jour. Sci., 3d ser., v. 21, p. 505-506.
Blake, W. P., 1856, Review of a portion of the geological map of the
United States and British Provinces in North America by Jules
Marcou: Am. Jour. Sci., 2d ser., v. 22, p. 383-388.
Bureau of Mineral Resources, Geology, and Geophysics, 1965, Geo-
logical map of the World; Australia, and Oceania, sheets 6, 7, 11,
12: Canberra, Australia. Scale 1:5,000,000.
Burke, Kevin, and Dewey, J. F., 1973, Plume-generated triple junc-
tions; key indicators in applying plate tectonics to old rocks: Jour.
Geology, v. 81, p. 406-433.
Butts, Charles, 1945, Description of the Hollidaysburg and Hunting-
don quadrangles, Pennsylvania: U.S. Geol. Survey Geol. Atlas
Carlson, C. G., 1969, Bedrock geologic map of North Dakota: North
Dakota Geol. Survey Misc. Map M-10. Scale 1:1,000,000.
Cohee, G. V., chm., 1962, Tectonic map of the United States, exclusive
of Alaska and Hawaii, by the United States Geological Survey
and American Association of Petroleum Geologists: U.S. Geol.
Survey, Scale 1:2,500,000.
Darrah, W. C., 1951, Powell of the Colorado: Princeton Univ. Press,
Princeton, N.J., 426 p.
Dutton, C. E., and Bradley, R. E., 1970, Lithologic, geophysical, and
mineral commodity maps of Precambrian rocks in Wisconsin:
U.S. Geol. Survey Misc. Geol. Inv. Map I-631. Scale 1:500,000.
Emerson, B. K., 1917, Geology of Massachusetts and Rhode Island:
U.S. Geol. Survey Bull. 597, 289 p.; map, scale 1:250,000.
Emery, K. O., and Uchupi, Elazar, 1972, Western North Atlantic
Ocean; topography, rocks, structure, water, life, and sediments:
Am. Assoc. Petroleum Geologists Mem. 17, 532 p.
Fisk, H. N., 1944, Geological investigation of the alluvial valley of the
lower Mississippi River: Mississippi River Comm., Vicksburg,
Miss., 78 p., maps.
Flint, R. F., chm., 1959, Glacial map of the United States east of the
Rocky Mountains, compiled and edited by a committee of the
Division of Earth Sciences, National Research Council: Geol. Soc.
America. Scale 1:1,750,000.
Frazer, Persifor, 1888, A short history of the origin and acts of the
International Congress of Geologists, and of the American Com-
mittee delegates to it: Am. Geologist, v. 1, p. 3-11, 86-100.
Geological Survey of Canada, l969, Geological map of Canada, R. J.
W. Douglas, compiler: Canada Geol. Survey Map 1250A. Scale
Gilbert, G. K., 1887, The work of the International Congress of
Geologists: Am. Jour. Sci., 3d ser., v. 34, p. 430-451.
Goddard, E. N., chm., 1965, Geologic map of North America, by the
North American Geologic Map Committee: U.S. Geol. Survey.
Gray, Carlyle, and others, 1960, Geologic map of Pennsylvania: Penn-
sylvania Geol. Survey. Scale 1:250,000.
Guettard, J. E., 1752, Carte minralogique o l'on voit la nature des
terraines du Canada et la Louisiane, in Mmoire dans laquel on
compare la Canada la Suisse par rapport ses mineraux: His-
toire de l'Acadmie Royal des Sciences, Paris, 189 p. Map.
Hack, J. T., 1955, Geology of the Brandywine area and origin of the
upland of southern Maryland, in Geology and soils of the Bran-
dywine area, Maryland: U.S. Geol. Survey Prof. Paper 267-A, p.
Hall, James, 1843, Geology of New York, Part 4, comprising the
survey of the Fourth Geological District: Albany, N. Y., 683 p.
Map, scale 1:1,850,000.
(Hall, James), 1854, Notice of a geological map of the United States
and the British Provinces of North America, with explanatory
text, geological sections, and plates of fossils which characterize
the formations, by J. Marcou: Am. Jour. Sci., 2d ser., v. 17, p.
Hall, James, and Lesley, J. P., 1857, Map illustrating the general
geological features of the country west of the Mississippi River, in
Emory, W. H., Report of the United States and Mexican Boundary
Survey: U.S. 34th Cong., 1st Sess., Senate Ex. Doc. 108, 2 v.
Hitchcock, C. H., 1881, Geological map of the United States (with
explanatory text, 29 p.): New York. Scale 1;1,266,200.
----- 1887, The geological map of the United States: Am. Inst. Min.
Eng. Trans., v. 15, p. 465-488. Map, scale 1:7,000,000.
Hitchcock, C. H., and Blake, W. P., 1874, Geological map of the United
States, compiled from sources mentioned in the text, in Walker,
F. W., ed., Statistical Atlas of the United States, based on the
results of the Ninth Census, 1870, compiled under the authority
of Congress: Washington, pl. 12-14, and p. 6-9. Scale 1:7,000,000.
Hitchcock, Edward, 1854, Outlines of the geology of the globe, and of
the United States in particular, with two geological maps, and
sketches of characteristic American fossils: Boston, 136 p., maps.
Horberg, Leland, 1945, A major buried valley in east-central Illinois
and its regional relationships: Jour. Geology, v. 53, no. 5, p.
Huntting, M. T., Bennett, W. A., Livingston, V. E., Jr., and Moen, W.
S., 1961, Geologic map of Washington: Washington Div. Mines
and Geology. Scale 1:500,000.
James, Edwin, 1823, Account of an expedition from Pittsburgh to the
Rocky Mountains, performed in the years 1819 and 1820, under
the command of Major Steven H. Long: Philadelphia, 2 v., 503 and
442 p., map.
Janssen, R. E., 1952, The history of a river: Sci. American, v. 186, p.
Jillson, W. R., 1950, The geological map of the United States--a
narrative outline and annotated bibliography, 1752-1946:
Frankfort, Roberts Printing Co., 23 p.
Jonas, A. I., 1932, Structure of the metamorphic belt of the southern
Appalachians: Am. Jour. Sci., 5th ser., v. 24, no. 9, p. 228-243.
King, P. B., compiler, 1969, Tectonic map of North America: U.S.
Geol. Survey, scale 1:5,000,000.
Kransky, L. I., 1964, Geological map of the northwestern part of the
Pacific mobile belt within the U.S.S.R.: Ministry of Geology of the
R.S.F.S.R. Scale 1:1,500,000.
Krinitzsky, E. L., and Turnbull, W. J., 1967, Loess deposits of Missis-
sippi: Geol. Soc. America Spec. Paper 95, 64 p.
Lewis, J. V., and Kmmel, J. B., 1910-12, Geologic map of New Jersey
(revised in 1931 by H. B. Kmmel, in 1950 by M. E. Johnson): New
Jersey Dept. Cons. and Econ. Devel. Atlas Sheet 40. Scale
Logan, W. E., and others, 1863, Report on the geology of Canada:
Canada Geol. Survey Rept. Prog. to 1863, 983 p.
Logan, W. E., (and Hall, James), 1866, Geological map of Canada and
the adjacent regions, including part of other British Provinces
and of the United States: Canada Geol. Survey. Scale 1:1,584,000
Longwell, C. R., chm., 1944, Tectonic map of the United States, pre-
pared under the direction of the Committee on Tectonics, Na-
tional Research Council: Am. Assoc. Petroleum Geologists. Scale
Lyell, Charles, 1845, Travels in North America in the years 1841 and
1842, with geological observations on the United States, Canada,
and Nova Scotia: New York and London, 2 v., 316 and 272 p. Map,
scale 1:7,620,000. (For sources of map, see v. 2, p. 198-219.)
McCracken, M. H., and others, 1961, Geologic map of Missouri: Mis-
souri Div. Geol. Survey and Water Resources. Scale 1:500,000.
McGee, W J, l885a, Administrative report: U.S. Geol. Survey 5th
Ann. Rept. for 1883-84, p. 34-41.
-----compiler, 1885b, Map of the United States exhibiting the pres-
ent state of knowledge relating to the areal distribution of the
geologic groups: U.S. Geol. Survey 5th Ann. Rept. for 1883-84, pl.
2, scale 1:7,115,000.
----- 1894, Reconnaissance map of the United States, showing the
distribution of the geologic systems so far as known: U.S. Geol.
Survey 14th Ann. Rept. for 1892-93, pl. 2, scale 1:7,115,000.
Maclure, William, 1809, Observations on the geology of the United
States, explanatory of a geological map: Am. Philos. Soc. Trans.,
v. 6, 411 p. Map.
----- 1817, Observations on the geology of the United States of
America; with some remarks on the effect produced on the nature
and fertility of soils, by the decomposition of the different classes
of rocks: Am. Philos. Soc. Trans., n. ser., v. 1; also Philadelphia,
Abraham Small, 127 p. Map.
Marcou, Jules, 1855, Rsum explicatif d'une carte gologique des
tats-Unis et des provinces anglais de l'Amrique du Nord: Soc.
Gol. France Bol., 2d ser., v. 12, p. 813-936. Map.
Marcou, Jules, and Marcou, J. B., 1884, Mapoteca geologica
Americana; a catalogue of geological maps of America (North and
South), 1752-1881: U.S. Geol. Survey Bull. 7, 184 p.
Merrill, G. P., l906, Contributions to the history of American geology:
U.S. Nat Mus. Rept. for 1904, no. 135, p. 189-734.
Milici, R. C., Spiker, C. T., Jr., and Wilson, J. M., 1963, Geologic map
of Virginia: Virginia Div. Mineral Resources. Scale 1:500,000.
Newcomb, R. C., 1970, Tectonic structure of the main part of the
basalt of the Columbia River Group, Washington, Oregon, and
Idaho: U.S. Geol. Survey Misc. Geol. Inv. Map I-587. Scale
Nickles, J. M., 1923, Geologic literature on North America,
1785-1918: U.S. Geol. Survey Bull. 746, pt. 1, 1167 p. (1924).
Owen, D. D., 1843, On the geology of the Western States of North
America: Geol. Soc. London Quart. Jour., v. 2, p. 433-447, map.
Owens, J. P., compiler, 1967, Engineering geology of the Northeast
Corridor, Washington, D.C., to Boston, Massachusetts; Coastal
Plain and surficial geology: U.S. Geol. Survey Misc. Geol. Inv.
Map I-514-B. Scale 1:250,000.
Powell, J. W., 1882, Report of the Director: U.S. Geol. Survey 2d Ann.
Rept. for 1880-81, p. xi-lv.
-----1888, Methods of geological cartography in use by the United
States Geological Survey: Internat. Geol. Cong., 3d, Berlin, 1888,
Comptes rendus, p. 221-240.
-----1890, Report of the Director: U.S. Geol. Survey 10th Ann. Rept.
for 1888-89, p. 1-80.
Reed, E. C., Dreezen, V. H., Bayne, C. K., and Schultz, C. B., 1965, The
Pleistocene in Nebraska and northern Kansas, in Wright, H. E.,
Jr., and Frey, D. G., eds., The Quaternary of the United States:
Princeton Univ. Press, p. 187-202.
Richards, H. G., 1965, Pleistocene stratigraphy of the Atlantic
Coastal Plain, in Wright, H. E., Jr., and Frey, D. G., eds., The
Quaternary of the United States: Princeton Univ. Press, p.
Richmond, G. M., Fryxell, Roald, Neff, G. E., and Weis, P. L., 1965,
The Cordilleran ice sheet of the northern Rocky Mountains and
related Quaternary history of the Columbia Plateau, in Wright,
H. E., Jr., and Frey, D. G., eds., The Quaternary of the United
States: Princeton Univ. Press, p. 231-242.
Snchez Mejorada, S. H., and Lopez Ramos, Ernesto, compilers, 1968,
Carta geolgica de la Repblica Mexicana: Comite de la Carta
Geolgica de Mexico. Scale 1:2,000,000.
Service de la Carte Gologique de la France; Bureau de Recherches
Gologiques et Minires, 1968, Carte gologique de la France.
Sims, P. K., 1970, Geologic map of Minnesota; bedrock geology: Min-
nesota Geol. Survey Misc. Map M-14. Scale 1:1,000,000.
Sloan, R. E., 1964, The Cretaceous System in Minnesota: Minnesota
Geol. Survey Rept. Inv. 5, 64 p., 2 pl.
Snowden, J. O., Jr., and Priddy, R. R., 1968, Geology of Mississippi
loess, in Loess investigations in Mississippi: Mississippi Geol.
Survey Bull. III, p. 13-203.
Stegner, Wallace, 1954, Beyond the hundredth meridian; John Wes-
ley Powell and the second opening of the west: Houghton Mifflin
Co., Boston, 438 p.
Stose, G. W., and Ljungstedt, O. A., 1932, Geologic map of the United
States: U.S. Geol. Survey. Scale 1:2,500,000.
Tectonic Map Committee, Geological Society of Australia, 1971, Tec-
tonic map of Australia and New Guinea: Geol. Soc. Australia.
Thorp, James, and Smith, H. T. U., chm., 1952, Pleistocene Eolian
deposits of the United States, Alaska, and parts of Canada, com-
piled by the National Research Council Committee for the Study
of Eolian Deposits, Division of Geology and Geography: Geol. Soc.
America. Scale 1:2,500,000.
Tight, W. G., 1903, Drainage and modifications in southeastern Ohio
and adjacent parts of West Virginia and Kentucky: U.S. Geol.
Survey Prof. Paper 13, 111 p.
Weaver, K. N., and others, 1968, Geologic map of Maryland: Mary-
land Geol. Survey. Scale 1:250,000.
Willis, Bailey, 1906, Carte gologique de l'Amrique du Nord:
Internat. Geol. Cong., 1Oth, Mexico, 1906. Scale 1:5,000,000.
----- 1912, Index to the stratigraphy of North America: U.S. Geol.
Survey Prof. Paper 71, 894 p. Map by Bailey Willis and G. W.
Stose, scale 1:5,000,000.
----- 1947, A Yanqui in Patagonia, a bit of autobiography; Stanford
Univ. Press, Stanford, Calif., x., 152 p.
Willis, Bailey, and Stose, G. W., 1911, Geologic map of North America,
compiled by the United States Geological Survey in cooperation
with the Geological Survey of Canada and Instituto Geologico de
Mexico. Scale 1:5,000,000. (Also in Prof. Paper 71, 1912.)