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The Great Basin is a large, arid region of the western United States, commonly defined as the contiguous watershed region, roughly between the Rocky Mountains and the Sierra Nevada, that has no natural outlet to the sea. The Great Basin Desert is defined by the extent of characteristic plant species, and covers a somewhat different area. The Great Basin Culture Area, home to the Great Basin tribes also extends further to the north and east than the hydrographic basin.
The 200,000 square mile (500,000 square km) area covers most of Nevada and over half of Utah, as well parts of California, Idaho, Oregon and Wyoming. The Great Basin is not a single basin, but rather a series of contiguous watersheds, bounded on the west by watersheds of the Sacramento-San Joaquin and Klamath rivers, on the north by the watershed of the Columbia-Snake, and on the south and east by the watershed of the Colorado-Green.
Watersheds within the Great Basin include:
- Great Salt Lake - Utah, Idaho, Wyoming
- Death Valley - California, Nevada
- Honey Lake - California
- Humboldt Sink - Nevada (drainage of the Humboldt River, the longest river in the Great Basin)
- Mojave Desert - California
- Pyramid Lake - Nevada
- Black Rock Desert - Nevada, Oregon
- Carson Sink - Nevada
- Walker Lake - Nevada
- Harney Basin - Oregon
- Sevier Lake - Utah
Much of the Great Basin, especially across northern Nevada, consists of a series of isolated mountain ranges and intervening valleys, a geographical configuration known as the Basin and Range Province. Additionally the Great Basin contains two large expansive playas that are the lakebed remnants of prehistoric lakes that existed in the basin during the last ice age but have since largely dried up. Lake Bonneville, the prehistoric ancestor of the Great Salt Lake, covered much of Utah, leaving behind the Bonneville Salt Flats. Likewise Lake Lahontan extended across much of northwestern Nevada and neighboring states, leaving behind such remnants as the Black Rock Desert, Carson Sink, Humboldt Sink, Walker Lake, Pyramid Lake, Winnemucca Lake, and Honey Lake , each of which now forms a separate watershed within the basin.
The Basin and Range province's dynamic fault history has profoundly affected the region's water drainage system. Most precipitation in the Great Basin falls in the form of snow that melts in the spring. Rain that reaches the ground, or snow that melts, quickly evaporates in the dry desert environment. Some of the water that does not evaporate sinks into the ground to become ground water. The remaining water flows into streams and collects in short-lived lakes called playas on the valley floor and eventually evaporates. Any water that falls as rain or snow into this region does not escape out of it; not one of the streams that originate within this basin ever find an outlet to the ocean. The extent of internal drainage, the area in which surface water cannot reach the ocean, defines the geographic region called the Great Basin.
The Great Basin's internal drainage results from blockage of water movement by high fault-created mountains and by lack of sufficient water flow to merge with larger drainages outside of the Great Basin. Much of the present-day Great Basin would drain to the sea - just as it did in the recent Ice Ages - if there were more rain and snowfall.
The history of human habitation in the Great Basin goes back at least 12,000 years. Archaeological evidence of primitive habitation sites along the shore of prehistoric Lake Lahontan date from the end of the ice age when its shoreline was approximately 500 ft (150 m) higher along the sides of the surronding mountains.
At the time of the arrival of Europeans, the region was inhabited by a broad group of Uto-Aztecan-speaking Native American tribes known collectively as the Great Basin tribes, including the Shoshone, Ute, and Paiute. The first Europeans to encounter the area were the early Spanish explorers in the southwest in the late 18th century. By the early 19th century, fur trappers from the Hudson's Bay Company had explored the upper Basin in the Oregon Country. The first comprehensive and accurate map of the region was made by John C. Frémont during several voyages across the region in the 1840s.
The United States acquired complete control of the area through the 1846 Oregon Treaty (giving it the portion north of the 42nd parallel) and the 1848 Treaty of Guadalupe Hidalgo (giving everything as part of the Mexican Cession). The first large-scale white settlement in the region was by early Mormon pioneers in the late 1840s in the arable areas around Salt Lake City and the Cache Valley. The Mormons quickly established a provisional government and drafted a proposal for a new state, called the State of Deseret, that encompass the entire Great Basin, as well as the coast of southern California. The region became successively organized by the creation of the Oregon Territory in 1848, the admission of California to the Union in 1850, and the creation of the Utah Territory in 1850. The discovery of gold in California in 1848 brough waves of emigrants across the Great Basin along the California Trail, which followed the Humboldt River across Nevada.
The Basin has remained among the most sparsely-inhabited areas of the United States. The two largest cities in the basin are Salt Lake City, Utah on its eastern edge and Reno, Nevada on its western edge. Smaller cities in the basin include Carson City, Nevada, Provo, Utah, and Logan, Utah.
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