USGS Logo Geological Survey Professional Paper 294—K
The Rocks and Fossils of Glacier National Park: The Story of Their Origin and History


Mountain scenery of exceptional grandeur gives Glacier National Park its unique appeal. Here are found splendid alpine peaks with sharply chiseled faces, canyons separated from each other by narrow, intricately carved ridges, waterfalls, lakes, and glaciers tucked away in the higher valleys. Across the international boundary—an arbitrary, manmade line—lies Waterton Lakes Park. The two national parks are scenically and geologically a unit.

The many modern glaciers give the park its name, but the rugged landscapes that impress the visitor were carved by glaciers that have long since melted. Glaciers that exist today have shrunk markedly in recent years—some have disappeared entirely. The few glaciers visible from vantage points along the roads are difficult to distinguish at a distance from the many glistening snowfields which persist through the summer. All who possibly can should leave the roads and travel by foot, horse, or boat into the less accessible parts of the region. By such means one can easily obtain close views of glaciers or even reach them. For example, Sperry Glacier can be easily visited by foot or on horse. Figure 122 shows some of the striking views to be seen on this trip. Guided trips are available from the Many Glacier Hotel to Grinnell Glacier.

The farther one gets from the roads and other evidences of civilization, the greater will be the reward. Most of these trips are well within the capacity of a person in normal health. Opportunities to study glaciers and glacial effects, past and present, are fascinating, but to many visitors they are not the greatest of the recompenses of trips into the back country. The traveler may relax and get true rest even while unschooled muscles strain and tire and panting breath testifies to the rarity of the atmosphere. Snowfields disappear in midsummer from the immediate vicinity of the roads but they persist near the peaks, where they enliven the scenery. Visitors of all ages from the parched lowlands to the east or from crowded seacoast cities especially enjoy the opportunity to frolic with snowballs beneath a benign summer sun.

If observant and patient, one can watch wild animals, large and small. Some species found in the mountains of the park are becoming rare throughout the continent. To be sure, almost everyone has opportunity to see the scraggly bears that beg along the highways and raid garbage cans at the camps; and fortunate motorists may observe moose and other animals even from their car windows. Far more thrilling are the glimpses of big game obtained away from the roads, where the animals are in their natural setting: the playful deer, the dignified elk and moose, and elusive goats that are thoroughly at home among the bleak crags.

For obvious reasons hunting is forbidden within the park, but fishing is permitted. Devotees of the latter sport will find that hiking over the trails can bring ample rewards.

The mountains will be enjoyed and appreciated most fully by those who have some knowledge of their geologic background. This is true even if one is limited to hurried views from the roads; it is even more true if one is privileged to make leisurely and intimate acquaintance with the park through travel over the trails. The purpose of this publication is to give visitors such an understanding. It presents, briefly and simply, the events in the geologic history of the park.

Scientific investigation of the area began in 1882 when the noted explorer and geologist, Raphael Pumpelly traversed it. However, systematic geologic explorations were not begun until 1901, when Bailey Willis, who later joined the faculty of Stanford University, assisted by G. I. Finlay and Stuart Weller, made studies which led to important conclusions concerning the nature and origin of the mountains. The outstanding result of their investigation was the recognition of the tremendous, gently inclined fracture or fault that they named the Lewis overthrust. This fault is the dominant structural feature of the region. It underlies the mountains and is exposed along the eastern front of the Lewis Range.

It is not strange that geologic exploration should have been long postponed in view of the fact that until the turn of the century white men had very scant knowledge about this part of Montana. A few fur trappers and traders had entered it early in the 19th century, but they built no settlements in or near the mountains. In 1853, Pitamakan Pass was visited by A. W. Tinkham in an unsuccessful search for a route for a railroad across the mountains. Late in the century, reports of the presence of copper and gold deposits aroused enough interest to prompt the Federal Government to purchase most of the area of the present Glacier National Park from the Blackfeet Indians. Though the area was thrown open to prospecting, results of the ensuing search for ore deposits were meager; a few caved tunnels and pits in the park remind visitors of the activity of this period, which ended about 1903.

In 1892 the Great Northern Railway built its line along what is now the southern border of the park. About 1895 a log hotel was built on the shore of Lake McDonald, and a steamboat was put in operation there, testifying to an early realization of the value of the region for recreation. Shortly afterward, on the strength of ill-founded rumors of oil, a road was built northward from the foot of Lake McDonald. These gains in transportation facilities were followed by homesteading in nearby valleys.

In 1900 to 1902, Francois E. Matthes and R. H. Sargent made a topographic survey of the Chief Mountain quadrangle, the first of a series of quadrangles mapped by the United States Geological Survey in the region. This map was published in 1904 and thus was available to show the striking character of the topography when creation of a national park was advocated. Congress enacted legislation in 1910 establishing Glacier National Park. Mapping of the entire area containing the park was completed in 1912, on a scale of 1:125,000 (approximately 2 miles to the inch). Copies of this map, valuable for reference and as a guide in the field, may be purchased from the U. S. Geological Survey, Denver Federal Center, Denver, Colo., and at various stations in the park itself. Plate 51 is a copy of this map, reduced in size so as to be more easily handled and with shading added to bring out the main topographic features.

From 1911 through 1914, parties of geologists of the Geological Survey, under the direction of M. R. Campbell, undertook a comprehensive investigation of the geology of the park. The topographic map served as a base for the field work. Associated with Campbell were W. C. Alden, Eugene Stebinger, T. W. Stanton, and others. This work was never completed, and the only publications that resulted were short, nontechnical papers. However, at intervals Alden continued studies of glacial phenomena in and near the park. Stebinger cooperated with Alden and also worked extensively on the coal and oil resources of the adjacent plains. Some of the publications of these two men are listed in the bibliography at the end of the present paper, together with other pertinent publications.

FIGURE 122.—Gunsight Pass and Mount Jackson. Lake Ellen Wilson, in the middle distance, is connected by the thin ribbon of Lincoln Falls with Lincoln Lake, 1,400 feet below. The saddle-horse trail from Sperry Chalet and Lake McDonald Hotel crosses Gunsight Pass above Lake Ellen Wilson. Small glaciers are visible in the upper right. (Photograph by permission of the U. S. Army Air Corps.)

From time to time other geologists have studied various aspects of the geology of the region. For example, C. L. Fenton and M. A. Fenton, between 1931 and 1937, published several papers on the ancient sedimentary rocks (the Belt series), which make up most of the mountains of the park, and their fossils. In 1938 Marland Billings, of Harvard University, made a notable contribution concerning the Lewis overthrust. Many geologists have studied the Belt series and also younger formations preserved in parts of Montana, British Columbia, Alberta, and elsewhere, mostly in localities distant from Glacier National Park.

The work of all visiting geologists has been facilitated by officers of the National Park Service. Naturalists of the park staff have added to the body of geologic information. Their systematic yearly observations and measurements of the glaciers constitute important contributions to knowledge of glaciers in general. Two publications of the Glacier Natural History Association, both of which were written by James L. Dyson, of Lafayette College, long a ranger-naturalist of the park, provide convenient summaries of geologic and glacial data. Road and trail logs, in pamphlets, by former Park Naturalists G. C. Ruhle and M. E. Beatty, are valuable in directing visitors to specific features of geologic interest, as well as to many other things. These publications may be purchased in the park.

The present publication is an outgrowth of a project by the Geological Survey to prepare a new geologic map of Montana. Field work on this project was begun by C. P. Ross in 1946, and it soon became evident that so little was known about the region just south of Glacier National Park that the geology could not be represented adequately even on the small scale of the proposed State map (1:500,000, or about 8 miles to the inch) without new field work. Consequently, the geologic mapping south of the park that began in 1948 was soon extended to include the park, and it continued through 1950. As a part of the investigation, study of the fossils (mainly algal) in the Belt series was begun by Stephan Nordeng in 1950 and was continued through 1953 by Richard Rezak.

This account of the geology of Glacier National Park is based on reports on the field work of 1948 to 1953. The one that deals with the general geology is by C. P. Ross and will be published by the Geological Survey. The one that concerns the algae, by Richard Rezak, was published by the Geological Survey in 1957. These reports and the geologic maps accompanying them incorporate data collected by Campbell and his coworkers many years ago. If it were not for these earlier studies the reports and maps would be far less comprehensive than they are. However, more information must be gathered before the geology of the region may be satisfactorily understood in all its details. Readers desiring more technical and detailed information than the present paper affords may wish to consult the reports listed in the selected bibliography.

In the preparation of the present paper, invaluable advice and assistance have been given by Ruth C. Ross, Fritiof M. Fryxell, G. D. Robinson, and others. In particular, Fryxell's experience in writing papers of this type contributed materially to the arrangement and phrasing of this paper.

The character, relative ages, and interrelations of the rock units successively deposited, ranging from the oldest exposed (the Belt series) to the deposits being laid down today, constitute the principal evidence from which the geologic history of the region can be deduced. Therefore, a table outlining the facts is offered as appendix A. The table contains some of the technical names used in the text to indicate the different geologic ages and rock units, including subdivisions of the Belt series. It is customary to name individual rock units after geographic features where the units were first studied and, generally, where they are well exposed. Thus the Belt series takes its name from the Big Belt Mountains and the Little Belt Mountains in central Montana. Another table that shows the approximate span in years of the major geologic time units is presented as appendix B.

In summary, information gathered by many geologists in the course of more than half a century, coordinated and amplified as a result of recent field work by the writers and their associates, has made it possible to decipher the geologic history of the Glacier National Park region. That history may now be sketched with confidence in regard to the correctness of its broader features. Some questions remain unanswered or only partly answered; some details are only hazily appreciated; some may still be unsuspected. Not only will additional facts be learned, but interpretations of those now known will be modified as the science of geology itself grows.

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Last Updated: 08-Jul-2008