Source data for previous geologic maps of the United States are plentiful, so we have chosen here to present a narrative account, describing the circumstances under which the maps were prepared and commenting 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 listing 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. Interesting 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 "Contributions 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 Pangborn, curator of these maps, for his generous assistance.


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, showing the nature of the terrains of Canada and Louisiana" ("Carte minéralogique où l'on voit la nature des terrains du Canada et de la Louisiane"), by the French geologist Jean Étienne 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 certain, 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 Breton 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 reported between the Atlantic Coast and the Rocky Mountains.

Aside from this primitive effort, the first geologic map of the United States is that published by William Maclure in 1809, of which a revised version appeared in 1817. 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.

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Figure 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 the originals.

FIGURE 1 (Full Resolution - 365 kb)

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To 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 "remarks on the effect produced on the nature and fertility of the soils by the decomposition of the different classes of rocks."

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 Mountains, New England, and the Piedmont Province; his "Transitional Rock" to the folded Paleozoic of the Appalachians; 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 publication, 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 stratigraphy in a large part of the country. The map includes not only Hall's survey in New York but also his reconnaissance 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 expeditions, 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. (The sources of the map are described 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, Cretaceous, 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 westward to its present conterminous limits by various acquisitions, which greatly expanded the field for geological exploration and mapping and also enlarged the problem of making a geological map of the United States.

Between 1853 and 1858, Jules Marcou produced a succession of geological maps of the United States, the later ones extending to the Pacific Coast. 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 to do.

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 boundary 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 by Marcou.

Less commendable than these was a contemporary map of the United States by Edward Hitchcock, professor of geology at Amherst College, which accompanied his "Outlines of the geology of the globe, and of the United States in particular" (1854). 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 Boué's "Geological Map of the World," with a few emendations--with such absurd results that the map would not deserve notice except for the eminence of its author.

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Figure 2.--Geology of the United States and adjacent parts of Canada as represented by Lyell (1845). Original map in color.

FIGURE 2 (Full Resolution - 338 kb)

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Figure 3.--Geology of the United States and adjacent parts of Canada as represented by Marcou (1855) Original map in color.

FIGURE 3 (Full Resolution - 401 kb)

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Figure 4.--Geology of the United States and adjacent parts of Canada as represented by Edward Hitchcock (1854). Original map in color.

FIGURE 4 (Full Resolution - 356 kb)

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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, representation 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).

As a result of the new surveys assembling a reasonably expressive geologic map of the whole country became 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 reports, notably in the "Statistical Atlas of the United States" that accompanied the report of the Ninth Census 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).


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 knowledge 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 cartography, his extended personal knowledge of American terranes, and his familiarity with American geological 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 colored, but in the western third only the areas mapped by the various Territorial Surveys are colored, the remainder being left blank. 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 unpublished 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 explorers can seldom be accurately coordinated with those recently published, 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 Mexico, 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 (Hitchcock, 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 revised version of the official map, again with the authorship 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."

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Figure 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.

FIGURE 5 (Full Resolution - 369 kb)

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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, especially 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 obscured 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 afterwards, when Willis became Geological Assistant to Director C. D. Walcott, Stose became Map Editor; nevertheless, Willis and Stose continued their collaboration 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 permanent 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 Géologique de l'Amérique du Nord" (Willis, 1906). It then appeared more desirable to perfect this preliminary rendering of North American geology than to continue on the proposed Geologic Map of the United States. An improved version of the Geologic Map of North America was virtually 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 71 (1912).

On the Geologic Map of North America of 1912 extensive 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, northern 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 assembled 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 and 1929.


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, although 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 Congress 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 compilations 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 obtain manuscript data, especially from State Maps that were in process of compilation. Nevertheless, adequate source maps were still lacking for much of the northwestern part of the country, so Stose and Ljungstedt, with the aid of local specialists, made original compilations 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 preparation of a Geologic Map of Virginia.

The resulting map, attractively printed in many colors, 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 printing was exhausted. The map represents the best summary that could be made in its time, not only of the areal geology of the country, but also of the prevailing geological philosophy. Any apparent imperfections that we might now see in the map should be viewed in this context.

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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 region 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 representation not possible at the time. Thus, the "Carboniferous System" is now divided into the Mississippian, 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 correlation 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 precision. 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" granites 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, Arthur 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 supposed "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 substantiated 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. Emerson (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 Interior States.

Part 3 - The Geologic Map of the U. S.
Part 4 - References Cited
Part 1 - Table of Contents, and Introduction


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