PURPOSE

The object of this report is to present the results of a search of the geologic and paleontologic literature for facts and inferences concerning the geological and paleontological history of the region surrounding Scotts Bluff National Monument. The information presented has been obtained principally from the literature, the sources of which are frequently referred to and are all included in the bibliography. Much of the information was obtained from personal interviews with members of the staff of the Museum of Vertebrate Paleontology and the Department of Paleontology at tho University of California. Free use was made of the library of the University of California, the Geology Library, and Matthew Library. This work was done under the direction of the Field Division of Education of the National Park Service.

LOCATION AND PHYSIOGRAPHY

Scotts Bluff National Monument is located near the center of Scotts Bluff County in Western Nebraska, and borders the North Platte River. It is situated near the towns of Gering and Scotts Bluff and may be reached by a branch of the Union Pacific System, the Chicago, Burlington and Quincy Railroad, or by an automobile road extending through the North Platte Valley. The monument has a total area of 1,893.83 acres which includes the conspicuous promontory of Scotts Bluff, a celebrated and historic landmark of the early days of travel along the Oregon Trail. It was created as a National Monument by Congress December 12, 1919.

This region is situated in the western portion of North America known as the Great Plains, an extensive, eastwardly sloping surface extending from the foothills of the Rocky Mountains to the western margin of the Mississippi basin.

To the north this plain terminates in Pine Ridge, a northward facing escarpment extending from Southern South Dakota thru Northwestern Nebraska and into Wyoming, beyond which the old surface had been largely destroyed by the erosive action of the White and Cheyenne Rivers. To the south the plain has an extensive development in Western Kansas and Texas. In Western Nebraska the surface of the high plain is confined to the larger interstream areas such as that lying between the Niobrara River and the North Platte River, that between Pumpkinseed Valley and Lodgepole Creek, and that lying to the south of Lodgepole Creek. In the region of Scotts Bluff, isolated remnants of this surface are represented in the irregular ridge lying to the south of the valley of the North Platte and separated from the main portion of the tableland to the south of Pumpkinseed Valley. Although the sum it of this ridge lies about ten miles south of the North Platte River, several lateral ridges extend almost to the river and form conspicuous bluffs, these being Scotts Bluff, Castle Rock, and Chimney Rock. Headward erosion of some of the streams draining this area resulted in the removal of materials from behind, leaving the projecting portions of former spurs standing as isolated pinnacles or mesas. An explanation of the complete isolation of this ridge and of the wide depression to the south now occupied by Pumpkin Creek has been proposed by Darton. (Darton, N. H., 1905, p. 22.) Along the sides of Pumpkinseed Valley, at levels considerably above the present valley floor, have been found rather extensive deposits of coarse gravels derived from the Rocky Mountains and similar in character to those found in the terraces of the North Platte River. It seems very probable that at one time a branch of the North Platte River flowed thru Pumpkinseed Valley making the ridge lying to the north an island in the midst of a wider Platte River. Subsequently the north channel of the river became more deeply eroded causing the river to confine all of its waters to that channel just as at present.

In the latitude of Scotts Bluff the surface of the Great Plains has an elevation of about 4300 feet above sea level at the one hundred and third meridian and gradually increases in elevation westwardly to nearly 5000 feet in the vicinity of the Wyoming line. In the southwest Banner County and in the extreme portion of Nebraska, altitudes of over 5300 feet are attained, these constituting the highest land in the state. Scotts Bluff, at one time believed to be the highest point, (Yard, R. S., Nat. Parks Portfolio 6th ed. revised by Isabelle F. Story, U. S. Govt. Printing Off. Washington, 1931.) has an elevation of 4662 feet.

One of the most interesting physiographic features of the Northern Great Plains is the badland topography so extensively developed in the Big Badlands of South Dakota and Northwestern Nebraska as well as in numerous smaller areas such as that developed at the base of Scotts Bluff. The name "Badlands" apparently had its origin in the literal translation of Mauvaisos Torres of the early French Canadian trappers who in turn derived it from the still earlier Mako Sicha (Mako, land; Sicha, bad) of the Dakota Indians. (O'Harra, C. C., 1920, p. 19).

Badland topography is solely an expression of erosive agoncics acting in such a way as to produce a labyrinth of steep-side, irregular gullies branching and rebranching into smaller and smaller rivulets until usually little level surface remains. The region also is often studded with symmetrical columns or with grotesque shaped mounds and tables. Topography of this sort is the result of erosion controlled in part by climatic conditions and in part by the stratigraphic and lithlogic nature of the deposits. The chief factors in its formation are: a climate with low rainfall usually concentrated into heavy showers; a scarcity of deep-rooted vegetation; slightly consolidated and nearly homogeneous, fine-grained sediments lying at a considerable height above the main drainage channels and in a nearly horizontal position. Such a country offers innumerable difficulties for travel and one can easily understand why the name, Mauvaises Torres.