DESERT, The Great American. The North American deserts possess all the physi °graphic, geologic and climatic elements which distinguish the African desert of Sahara. The chief difference between the two regions is the relatively larger area of the Sahara, the arrange ment of the topographic units and the occur rence in the Great American Desert of a wealth of mineral resources which the Sahara does not possess. Through the application of modern mechanical agencies by American energies and brain, its wastes have become inhabited by an intelligent and progressive people, and its arid hills and plains to yield a wealth twice as much per capita as that of any other portion of the United States.
The vast stretches lying between the Sierra Nevada and California and the eastern Cordil leran ranges (Rocky Mountains) in the United States, and between the Pacific Ocean and the eastern Sierra Madre of Mexico, constitutes the Great American Desert.
Of the total area of the Cordilleran prov ince, three-eighths are forested mountains, one eighth plateau and one-half waterless, treeless, turfiess mountain and valley desert. The des erts occur in Nevada, Utah, eastern and south ern California, Arizona, New Mexico and all of Texas west of the Pecos, 550,000 square miles. The American Desert is international, however, for in addition to the above area within the United States, it continues south ward into Mexico, where it includes most of the states of Sonora, Chihuahua, Coahuila, San Luis Potosi and Sinaloa — another 500,000 square miles—making a total of 1,050,000 square miles, which although one-third the area is as truly a desert in every natural sense as is the Sahara, which embraces an area of 3,500, 000 square miles, and has a population of 2,500,000 people.
In its entirety (with a few exceptional for ested summits) this desert province is one of barren, stony mountain ranges, separated by equally barren stretches of desert plain, an aggregation of elongated arid plains and lower mountain ranges, which mostly follow the avial line of the Cordilleras. The individual deserts have many names, and each differs from the other in some minor aspects.
From a technical point of view an arid des ert in its ultimate analysis is a region in which the rainfall is insufficient to produce run-off.
The light rainfall, striking the heated rock sur faces and sandy soils, is soon evaporated or drunk in; even the large bodies of water which may start down the mountain sides as roaring torrents usually die out at the margins of the plains. These waters are highly charged with mineral salts derived from the heated rock sur faces, and these salts are readily redeposited upon the surface or in the interstices of the permeable sands. The torrents locally transport the rock debris — boulders, pebbles and powder — from one locality to another, but only for short distances; and hence the desert plains are usually composed of the debris of the adjacent mountains, which in more humid regions of ample run-off would have been carried to the sea. The expansion and contraction from the daily temperature causes the desert rocks to fracture in situ into the desert waste. This is distributed by wind and torrent, and hence the features of the desert are largely air-made as well as water-wrought.
The scarcity of _moisture results in the ab sence of vegetation of the root-twining, soil gathering and soil-making type that distin guishes the humid region. Every plant and species attests the aridity of the country. Exactly as in the Sahara, these plants are thorny, coriaceous bushes and shrubs of the cactus, aloe and acacia families, adapted to withstand their droughty environment and to defend themselves from attack by man or beast.
Physiographically there are two sub-prov inces of the Great American Desert, lying to the east and to the west of the western Sierra Madre and Colorado Plateau, respectively. The westernmost of these may be termed the Nevadan and the eastern the Chihuahuan. The western, or Nevadan, Desert occupies much of the area of Utah, Nevada, Arizona, southern and east ern California in the United States, and the states of Sonora and Sinaloa in Mexico. The Chihuahuan Desert occupies the vast area of country lying between the eastern and western Sierra Madre of Mexico and their northern continuation into southern New Mexico and Texas west of the Pecos, and is the so-called Mexican Plateau.