Great Basin

Great Basin, semiarid, N section of the Basin and Range province, the intermontane plateau region of W United States and N Mexico. Lying mostly in Nevada and extending into California, Oregon, Idaho, and Utah, it is bordered by the Sierra Nevada on the west, the Columbia Plateau on the north, the Rocky Mts. on the northeast, the Colorado Plateau on the east, and the Mojave Desert on the south.

Land

The region is a complex topographic basin, the surface of which is broken by numerous fault-block mountains, trending mostly north-south and rising sharply in places to more than 10,000 ft (3,048 m) above dry, sediment-floored basins. Death Valley, 282 ft (86 m) below sea level, is the lowest basin; it is also the hottest (134°F;/57°C; in the shade is the highest temperature recorded) and one of the driest (less than 3 in./7.6 cm of rain annually) parts of North America. Throughout the Great Basin rainfall is limited (2–20 in./5.1–51 cm annually) and sporadic.

The region was recognized as an area of interior drainage by J. C. Frémont, who explored (1843–45) and named it. The rivers of the region have no outlet to the sea; they either dry up as they cross the parched terrain, like the Humboldt, or empty into large lakes or into playas that temporarily fill with water after heavy rain. Klamath and Utah lakes contain freshwater; most other lakes are brackish or salty. The lakes are remnants of a much larger system of ancient lakes that occupied the region during the Pleistocene epoch: Great Salt, Sevier, and Utah lakes are remnants of glacial Lake Bonneville (see under Bonneville Salt Flats); North Carson, South Carson, Walker, Honey, Pyramid, and Winnemucca are remnants of glacial Lake Lahontan; and glacial Lake Manly is thought to have occupied Death Valley.

Economy

Although Nevada and Utah experienced significant growth in the 1970s and 80s, the Great Basin remains one of the least populated areas of the United States. In recent decades, its traditional economic activities, mining and ranching, have been superseded by manufacturing and tourism. In addition, several military installations, including a nuclear testing site in Nevada, have been established since the 1950s and a concentration of aerospace, defense, and electronics firms has sprung up around them.

The mining industry in the Great Basin traces its roots to the 1850s, when gold and silver were discovered in Death Valley; the discovery of silver at the Comstock Lode near Virginia City, Nev., in 1859 attracted a new influx of settlers. The output of gold from mines in both Nevada and Utah remains high. Mercury and barite are also mined in Nevada; in Utah, beryllium, uranium, molybdenum, and silver are mined. Copper mines, formerly the mainstay of the regional economy, began to decline in the 1970s and have largely fallen into disuse. A variety of commercial salts are processed at chemical plants near the Great Salt Lake. Intensive forms of cattle production, based on irrigated feed crops, are concentrated along the Humboldt and Reese rivers and along streams draining into the margins of the Great Basin from the Wasatch Mts. and the Sierra Nevada.

Great Basin National Park (77,180 acres/31,258 hectares) is located in the South Snake Range of E Nevada. It has exceptional scenic and geologic attractions, including Lehman Caves and Wheeler Peak (the highest point in the park, with Nevada's only glacier and groves of bristlecone pines, the oldest living trees). It was designated a national park in 1986. See National Parks and Monuments (table).

Bibliography

See W. D. Thornbury, Regional Geomorphology of the United States (1965); J. McPhee, Basin and Range (1981); W. Fiero, Geology of the Great Basin (1986); G. G. Cline, Exploring the Great Basin (1988).

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Great Basin

a semiarid region of the western US, between the Wasatch and the Sierra Nevada Mountains, having no drainage to the ocean: includes Nevada, W Utah, and parts of E California, S Oregon, and Idaho. Area: about 490 000 sq. km (189 000 sq. miles)

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Great Basin 

a highland in the North American cordillera, in the western United States. It unites territories located between the Sierra Nevada and the Cascade Mountains in the west and the Rocky Mountains in the east and has no runoff into the ocean. The basin covers an area of more than 500,000 sq km. It consists of a multitude of short ranges (elevation up to 3,900 m) and broad interconnected basins. The relief was formed on a Precambrian-Mesozoic fold foundation which was subjected to fault dislocations in the Cenozoic era. These movements were accompanied by volcanic activity. Most of the basins are of tectonic origin; the ranges that separate them are horst blocks. The absence of external runoff and an outlet for the products of destruction of the ranges led to the filling of the basins with a thick layer of rocky and sand-clay deposits, which partially scoured the primary mountain relief. The climate is sharply continental, subtropical for most of the basin, and temperate in the north. Summers are hot and cloudless, and winters are cool, with frequent fog. The average July temperature is 20°–22°C (maximum 56.7° C); in January the average is 0°–2° C (minimum –30° C; to –60° C in the mountains). The average annual precipitation is about 200 mm, in individual basins less than 100 mm, and on the western slopes of the mountains, up to 500 mm. The largest part of the Great Basin is irrigated by short, episodic (primarily winter) waterways which end in basins. The main river is the Humboldt. The largest lakes include the Great Salt Lake, Pyramid Lake, Sevier Lake, and Utah Lake. Most of the lakes remain on the site of larger bodies of water that existed in the Pleistocene epoch—Lake Bonneville and others. Artesian wells, located most frequently at the outer edges of the basins, are an important source for irrigation. The most widely distributed soils are brown sierozems, solonchak, and saline (in the basins), and mountain chestnut (in the mountains). Most of the territory is semi-desert; in the north (north of 37° N lat.) there are grass-sagebrush and goosefoot, and in the south, creosote with patches of cactus and agave. The more moist mountain slopes are covered with stunted pine and juniper forests. The most widely distributed animals include reptiles, especially rattlesnakes, poisonous lizards, and horned toads. There is agriculture in the irrigated areas.

G. M. IGNAT’EV