GREAT BASIN, THE, so named by John C. Fremont, who was the first to gain an adequate conception of its character and extent, is a roughly triangular region including about 200,000 sq.m. in the western part of the United States, between the Wasatch mountains and the Sierra Nevada. It is about Boo m. long from north to south and about 50o m. broad in its widest part, at its north end. Most of it is in Nevada and Utah, but a large part is in California, and it includes small areas in Oregon, Idaho and Wyoming. It is not, as its name might suggest, a single basin-shaped depression that gathers its waters to a common centre, but it is divided into many independent drainage basins, the water of none of which finds outlet from the region. Its surface features are diverse, including flat valleys and rugged mountains with high peaks. The general level of the basin is highest near its centre, from which it descends notably toward the south. Death valley and the valley that contains the Salton sea, both in southern California, lie in part below sea-level. The whole of the Great Basin has been considered a vast desert, although that term is more properly applied only to the Great Salt Lake and Carson deserts, in its northern part, and to the Mohave, Ralston and Amargosa deserts, in its south-western part. It includes salty and alkaline deposits, barren mud playas into which water that' falls in rainstorms gathers for short periods and stony wastes where mountain streams have formed alluvial fans at their mouths. Many of the mountains and valleys trend north and south and appear to be of a peculiar type, exhibiting what has been called basin-range or fault-block structure, a type that has long been a subject of study and discussion by geologists.
The climate in widely separated parts of the Great Basin and at its greatly different altitudes ranges from nearly tropical to cool. The region is dry, the average annual rainfall being about 3 in. in its southern part and io to 12 in. in its northern part. The precipitation occurs mostly in short local showers, some of them so violent that they are called cloudbursts. The water of these storms cuts deep arroyos but soon evaporates. Few of the mountain streams flow out upon level land, and the water of those that do soon disappears or is dissipated by evaporation. In the northern part of the basin there are many permanent lakes, which, having no outlets, are saline. The largest of these is Great Salt Lake (q.v.). Among the other lakes in the northern part of the basin are Bear, Utah and Sevier lakes, and, farther west, Eagle, Pyramid, Winnemucca and Walker lakes and the Carson lakes. Humboldt river, the largest stream in the Great Basin. feeds North Carson lake.
On the higher levels in central Utah there are straggling forests, mainly of pine and cedar, and in northern Nevada scattered clumps of brush, among which greasewood (Sarcobatus) and several kinds of sage (Artemisia) are the most abundant. Most of the lowlands and lower mountains are treeless. Cottonwoods grow along the streams, and plants that can endure salt thrive along the margins of the bare playas. In the southern part of the basin grey desert plants and species of cactus and other thorny growths are common. In the spring the barren-looking land in places brings forth many beautiful and delicate flowers. Agriculture is restricted to a few irrigable areas, but sheep and cattle are grazed in some places. The vegetation becomes more varied and abundant with increase of altitude. Some of the most productive metal mines in the world have been developed in this region. The Mormons have planted orchards, gardens and fields of grain on the east side of Great Salt Lake. The Salt Lake desert, which lies west of the lake and which Fremont visited in 1842, is still a desert, and the Great Basin as a whole is very sparsely settled.
A hundred thousand years ago the climate of the basin was much moister than it is now. In the northern part there were then two large lakes, Lake Bonneville and Lake Lahontan.
See G. K. Gilbert in Surveys West of the One Hundredth Merid ian, vol. iii.; Clarence King and others, Report of the Fortieth Parallel Survey; G. K. Gilbert, "Lake Bonneville," U.S. Geological Survey Monograph I. (189o) ; also I. C. Russell, "Lake Lahontan," id., Monograph II., 1885. For a history of the discussion of basin range or fault-block structure see G. K. Gilbert, "Studies of Basin Range Structure," U.S. Geological Survey, Professional Paper (5928). (G. McL. Wo.)