James's Account of S. H. Long's Expedition, 1819-1820, part 4

by Edwin James; Stephen H. Long; Thomas Say

Of the Great Desert at the base of the Rocky Mountains

The portion of country which we design to consider under this division has an average width of five or six hundred miles, extending along the base of the Rocky Mountains from north to south: as far as we have any acquaintance with that range, consisting entirely of granitic sands, or of secondary aggregates made up of the detritus of that great chain of primitive mountains, there seems to be a degree of propriety in designating it by some name recognising relation to those mountains. It has been mentioned as the "Mexican desert;" a name sufficiently applicable, perhaps, to some portions of it, but one by no means to be extended to every part alike, as there can be little doubt of its occupying an extensive {277} portion of the interior of North America. That a similar desert region exists on the western side of the mountains, we have sufficient evidence; but whether as uninterrupted and as extensive, we have not the means of determining.

The Jesuit Venegas, speaking of the early history of California, says "Father Kino and his companions, after travelling thirty leagues from San. Marcelo, came to a small rancheria (Indian village); and leaving on the north the great mountain of Santa Clara, whose sides, for the length of a league, are covered with pumice-stone, they arrived at the Sandy Waste, on the 19th of March." Our information is, however, too limited to justify an attempt to fix the boundaries of this desert; we will, therefore, content ourselves with communicating the observations our opportunities have enabled us to make.

The channel of the Missouri, near the mouth of the Platte, discloses here and there rocks of horizontal limestone; which, from their peculiar character, we are disposed to consider as belonging rather to the Ozarks, than having any connection with the Rocky Mountains. These rocks appear at the lowest parts of the valleys, and are usually surmounted by extensive beds of soil, consisting principally of flinty sand in the most minute state of division, but variously intermixed with the remains of organized beings, and sometimes with calcareous and aluminous earth. Proceeding westward, the sand becomes deeper and more unmixed; not a rock or a stone, in place or out of place, is to be met with for some hundreds of miles. It is believed that no rocky bluffs appear along the valley of the Platte, within three hundred miles of its mouth, though a small part of this distance, on the lower portion of the river, has not hitherto been explored. The surface is not an absolute plain, but is varied with gentle undulations, such {278} as the draining of water, from an immense table of a light arenaceous earth, for a succession of centuries, may be supposed to have occasioned. The gradual intermixture of the exuviæ of animals and vegetables, with what was formerly a pure siliceous sand, has at length produced a soil capable of supporting a scanty growth of grasses; now almost the only covering of these desolate regions. Scales of mica, little particles of brownish felspar, and minute fragments of hornblende, may here be detected in the soil.

About four hundred miles west of the mouth of the Platte, a low range of sandstone hills crosses the country from south-west to north-east. The strata composing these hills have no perceptible inclination, and present appearances which indicate their deposition to have been nearly contemporaneous to that of many of our coal formations. It has already been suggested that this range may probably be a continuation of the Cotes Noir, or Black hills, said to contain the sources of the Shienne, the Little Missouri, and some branches of the Yellow Stone.[80]

These inconsiderable hills being passed, the surface again subsides nearly to a plain. The fine and comparatively fertile sand which prevailed to the east of the ranges, is exchanged for a gravel made up of rounded granitic fragments, varying in dimensions from the size of a six-pound shot to finish sand. This great mass of granitic fragments, evidently brought down by the agency of water from the sides and summits of the Andes, slopes gradually from their base, appearing, as far as examinations have extended, to correspond in some measure, in magnitude, to the elevation and extent of that part of the mountains opposite which it is placed. The minute particles derived from the quartzy portions of the primitive aggregates, being least liable to decomposition, have been carried to the greatest distance, {279} and now form the almost unmixed soil of the eastern margin of the great sandy desert. The central portions are of a coarser sand, with which some particles of felspar and mica are intermixed: nearer the mountains, pebbles and boulders become frequent, and at length almost cover the surface of the country.

The opinion above advanced, that the great sandy desert has resulted from the wearing down of the mountains, both before and since the retiring of the ocean, should, perhaps, be received with some caution. We have no foundation for the belief, but in the examinations which enabled us to discover that the materials composing both regions are similar in kind; that the granitic soils of the plain are precisely such as would result from the disintegration of the rocks now existing in the mountains; and that the numerous deep ravines and water-worn valleys traversing the mountains in various directions, indicate the change here supposed to have happened.

It is probable many parts of this extensive desert may differ from that traversed by the Platte, in having the surface more or less covered with horizontal strata of sandstone and conglomerate, instead of loose sand and pebbles. Indeed, there are many appearances indicating that a formation of this kind formerly extended down the Platte much farther than at present. From the minute account given in the narrative of the expedition, of the particular features of this region, it will be perceived that its eastern portions bear a manifest resemblance to the deserts of Siberia. The soils, and I believe the rocks, wherever any occur, are saline: plants allied to chenopodium and salsola are peculiarly abundant, as are the astragali and other herbaceous leguminæ; while trees and forests are almost unknown.

The surface of the sandy plain rises perceptibly towards the base of the mountains; and becoming constantly more and more undulating, is at length broken, disclosing some cliffs and ledges of micaceous {280} sandstone. Near the Platte this sandstone occurs in horizontal strata, sometimes divided by the beds of the streams, and forming low ridges parallel to the Rocky Mountains. Whether they continue in an uninterrupted line along the base of the mountains, we have not been able to ascertain. They are separated from the first range of primitive, by more elevated cliffs of a similar sandstone, having its strata in a highly inclined position. Behind these, occur lofty but uninterrupted ranges of naked rocks, destitute of any covering of earthy or vegetable matter, and standing nearly perpendicular. At a distant view, they present to the eye the forms of walls, towers, pyramids, and columns, seeming rather the effects of the most laborious efforts of art, than the productions of nature. When surveyed from the more elevated summits of the first granitic range, these immense strata of sandstone standing on edge, and sometimes inclining at various angles towards the primitive, resemble the plates of ice often seen thrown into a vertical position in the eddies and along the banks of rivers.