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Encyclopedia Britannica - Main :: GRA-GUI |
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GREAT BASIN , an area in the western Cordilleran region of the United States of America, about 200,000 sq. m. in extent, characterized by wholly interior drainage, a peculiar mountain system and extreme aridity. Its form is approximately that of an isosceles triangle, with the sharp
The Great Basin is not, as its name implies, a topographic cup. Its surface is of varied character, with many independent closed basins draining into lakes or " playas," none of which, however, has outlet to the sea. The mountain chains, which from their peculiar geologic character are known as of the " Basin Range type " (not exactly conterminous in distribution with the Basin), are echeloned in short ranges running from N. to S. Many of them are fault block
recent
recent
wash
Over the lowlands of the Basin, taken generally, there is an average precipitation of perhaps 6-7 in., while in the Oregon region it is twice as great, and in the southern parts even less. The mountains receive somewhat more. The annual evaporation from water surfaces is from 6o to 150 in. (6o to 8o on the Great Salt Lake). The reason for the arid climate differs in different sections. In the north it is due to the fact that the winds from the Pacific lose most of their moisture, especially in winter, on the western slopes of the Sierra Nevada; in the south it is due to the fact that the region lies in a zone of calms, and light, variable winds. Precipitation is largely confined to local showers, often of such violence as to warrant the name " cloud bursts," commonly applied to the heavy down-pours of this desert region. It is these heavy rains, of brief duration, when great volumes of water rapidly run off from the barren slopes, that cause the deep channels, or arroyas, which cros's the desert. Permanent streams are rare. Many mountains are quite without perennial streams, and some lack even springs. Few of the mountain creeks succeed in reaching the arid plains, and those that do quickly disappear by evaporation or by seepage into the gravels. In the N.W. there are many permanent lakes without outlet fed by the mountain streams; others, snow fed, occur among the Sierra Nevada; and some in the larger mountain masses of the middle region. Almost all are saline. The largest of all, Great Salt Lake, is maintained by the waters of the Wasatch and associated plateaus. No lakes occur south of Owens
Save where irrigation has reclaimed small areas, the whole region is a vast desert, though locally only some of the interior plains are known as " deserts." Such are the Great Salt Lake and Carson deserts in the north, the Mohave and Colorado and Amargosa (Death Valley) deserts of the south-west. Straggling forests, mainly of conifers, characterize the high plateaus of central Utah. The lowlands and the lower mountains, especially southward, are generally treeless. Cottonwoods line the streams, salt-loving vegetation margins the bare playas, low bushes and scattered bunch-grass grow over the lowlands, especially in the north. Gray desert plants, notably cactuses and other thorny plants, partly replace in the south the bushes of the north. Except on the scattered oases, where irrigation from springs and mountain streams has reclaimed small patches, the desert is barren and forbidding in the extreme. There are broad plains covered with salt and alkali, and others supporting only scattered bunch grass, sage bush
The successive explorations of B. L. E. Bonneville, J. C. Fremont and Howard Stansbury (18061863) furnished a general knowledge of the hydrographic features and geological lacustrine history of the Great Basin, and this knowledge was rounded out by the field work
late
See G. K. Gilbert in Wheeler Survey, U.S. Geographical Survey West of the Hundredth Meridian, vol. iii.; Clarence King and others in the Report of the Fortieth Parallel Survey (U.S. Geol. Exploration of the Fortieth Parallel) ; G. K. Gilbert's Lake Bonneville (U.S. Geological Survey, Monographs, No. 1, 1890), also I. C. Russell's Lake Lahontan (Same, No. I 1, 1885), with references to other publications of the Survey. For reference to later geological literature, and discussion of the Basin Ranges, see J. E. Spurr, Bull . Geol. Soc. Amer. vol. 12, 1901, p. 217; and G. D. Louderback, same, vol. 15, 1904, p. 280; also general bibliographies issued by the U.S. Geol. Survey (e.g. Bull . 301, 372 and 409).End of Article: GREAT BASIN If you wish, you can link directly to this article.
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