Great Basin

Great Basin, area of inland drainage in the western United States, between the Wasatch Range on the east and the Sierra Nevada and Cascade Range on the west. It includes most of Nevada and portions of Utah, Oregon, Idaho, and California, and forms a triangle, widest at the north, with a total area of about 543,900 sq km (210,000 sq mi). The basin has a gradual slope from the north, where the elevation is about 122 m (400 ft) above sea level, down to 86 m (282 ft) below sea level in Death Valley, California, in the south. The basin is unusual in that it is an area of interior drainage—that is, its waterways drain into desert flats, not into the sea. The Humboldt River in Nevada is the only perennial stream of any size rising in the interior, but on the borders numerous short streams act as feeders to a number of mostly saline lakes, including the Great Salt Lake and the Pyramid Lake. Within the basin lie several arid wastes—among them, Carson Sink and the Great Salt Lake and Mojave deserts. The basin was formed about 16 to 24 million years ago when sedimentary rock was uplifted and dropped by movement of geologic plates. During the Pleistocene epoch, the climate was damp and much of the northern and eastern portions of the basin was occupied by two large lakes, Lake Bonneville and Lake Lahontan.