GREAT BASIN, a vast region of interior drainage, a triangular plateau of North America, occupying the western part of Utah and nearly the whole of Nevada, parts of Oregon and California and extending at its northeast angle into Idaho. It is bounded on the west by the Sierra Nevada and on the east by the Wasatch Mountains, The base of the triangle at the north is 500 miles from east to west and the extent from north to south is 800 miles. The area is about 210,000 square miles, a little larger than France. It is traversed by numerous mountain ranges, irregular in arrangement; the valleys are mostly sinks, the chief drainage centre being Great Salt Lake (q.v.). The areas of greatest depression are to be found near the borders and the greatest elevation near the central part. The highest range is the East Humboldt, one peak of which, Mount Bonpland, is 11,321 feet in height. Volcanic masses form or conceal the original rocks of many of these ranges. The slopes and the geological markings show that the lakes and rivers which once existed within this region have become smaller and some have disappeared. Among the more notable of the extinct lakes are Bonneville and Lahontan. The greater portion of this section was once in the basin of the Columbia River. The Great Basin contains many streams and lakes (the latter for the most part salt) whose waters never reach the ocean, but are either taken up by evaporation or their waters sink in the desert sands. The mean annual rainfall ranges in different localities from 4 to 15 inches. The plateau is nearly destitute of trees and in general only the upper parts of the valleys are clothed with desert shrubs, their lower portions often being covered with muddy water or with several inches of alkaline salts left by evaporation. The chief arid places are the Great Salt Lake Desert, the Mohave Desert and the Carson Desert. This basin is rich in mineral wealth; gold, silver, iron ore and copper exist here in large quantities. The Great Basin is among the large interior drainage sections of the world; but the interior drainage basin of Asia is 23 times as great and the Sahara 16 times as great.