The Great Basin Desert is the largest US desert and covers 190,000 square miles (490,000 km 2 ). It is bordered by the Sierra Nevada Range on the west and the Rocky Mountains on the east, the Columbia Plateau to the north and the Mojave and Sonoran deserts to the south. The Great Basin Desert, unlike the Mojave or Sonora deserts, characteristically "lacks creosote bush" as defined by J. Robert Macey in a 1986 report distinguishing between "Great Basin scrub desert" and "creosote bush desert." [3] Rainfall within the Great Basin Desert region varies from seven to twelve inches per year. The Great Basin Desert includes several arid basins lacking Larrea tridentata (chaparral) such as the "Chalfant, Hammil, Benton, and Queen valleys," as well as all but the southeast portion of the Owens Valley. Conversely, the "Panamint, Saline, and Eureka valleys" have creosote bush, unlike the Deep Springs Valley which includes part of the Great Basin scrub desert. The Great Basin Desert is a cold desert caused by the rain shadow effect from the Sierra Nevada to the west. The predominant flora are "continuous shadscale and…sagebrush." The ecotone demarcating the north of the Mojave Desert is the edge of creosote bush habitat and is also the south demarcation of the Great Basin shrub steppe and Central Basin and Range ecoregions. [3] The ecotone is established by elevation increase, temperature decrease at higher elevations, and rainfall (less rain shadow at higher latitudes). Climate Climate varies throughout the Great Basin by elevation, latitude, and other factors. Higher elevations tend to be cooler and receive more precipitation. The western areas of the basin tend to be drier than the eastern areas because of the rain shadow of the Sierra Nevada. Most of the basin experiences a semi-arid or arid climate with warm summers and cold winters. However, some of the mountainous areas in the basin are high enough in elevation to experience an Alpine climate. Due to the region's altitude and aridity, most areas in the Great Basin experience a substantial Diurnal temperature variation. The Great Basin National Park, located in a central part of the Great Basin, provides perhaps the best example of a typical climate for the region. History Sediment build-up over thousands of years filled the down-faulted basins between ranges and created relatively flat lacustrine plains from Pleistocene lake beds of the Great Basin. For example, after forming about 32,000 years ago, Lake Bonneville overflowed about 14,500 years ago in the Bonneville Flood through Red Rock Pass and lowered to the "Provo Lake" level (the Great Salt Lake, Utah Lake, Sevier Lake, Rush Lake, and Little Salt Lake remain). Lake Lahontan, Lake Manly, and Lake Mojave were similar Pleistocene lakes. Paleo-Indian habitation by the Great Basin tribes began as early as 10,000 B.C. (the Numic-speaking Shoshonean peoples arrived as late as 1000 A.D.). Archaeological evidence of habitation sites along the shore of Lake Lahontan date from the end of the ice age when its shoreline was approximately 500 feet (150 m) higher along the sides of the surrounding mountains. The Great Basin was inhabited for at least several thousand years by Uto-Aztecan language group-speaking Native American Great Basin tribes, including the Shoshone, Ute, Mono, and Northern Paiute. Exploration of the Great Basin occurred during the 18th century Spanish colonization of the Americas. The first American to cross the Great Basin from the Sierra Nevada was Jedediah Strong Smith in 1827. Peter Skene Ogden of the British Hudson's Bay Company explored the Great Salt Lake and Humboldt River regions in the late 1820s, following the eastern side of the Sierra Nevada to the Gulf of California. Benjamin Bonneville explored the northeast portion during an 1832 expedition. The United States had acquired control of the area north of the 42nd parallel via the 1819 Adams–Onís Treaty with Spain and 1846 Oregon Treaty with Britain. The US gained control of most of the rest of the Great Basin via the 1848 Mexican Cession. The first non-indigenous settlements were connected with the eastern regions of the 1848 California Gold Rush, with its immigrants crossing the Great Basin on the California Trail along Nevada's Humboldt River to Carson Pass in the Sierras. The first American religious settlement effort was the Mormon provisional State of Deseret in 1849 in present day Utah and northern Nevada. They started settling the Great Salt Lake Valley in 1847. The Oregon Territory was established in 1848 and the Utah Territory in 1850. In 1869 the First Transcontinental Railroad was completed at Promontory Summit in the Great Basin. Around 1902, the San Pedro, Los Angeles and Salt Lake Railroad was constructed in the lower basin and Mojave Desert for California-Nevada rail service to Las Vegas, Nevada. To close a 1951 Indian Claims Commission case, the Western Shoshone Claims Distribution Act of 2004 established the United States payment of $117 million to the Great Basin tribe for the acquisition of 39,000 square miles (100,000 km 2 ). The Dixie Valley, Nevada, earthquake (6.6-7.1) in the Great Basin was in 1954. The Mojave and Colorado Deserts Biosphere Reserve (4 conserved areas) was designated in 1984, and in 1986, and 1994, the Great Basin National Park and the Mojave National Preserve were established. In 2009, the American Land Conservancy's Great Basin Program reserved the Green Gulch mule deer migration corridor as part of "over 80,000 acres [conserved] in Nevada and the Eastern Sierras". Settlements and Roads The Great Basin's two most populous metropolitan areas are Reno to the west and Salt Lake City to the east. The area between these two cities is sparsely populated, but includes the smaller cities of Delta, Elko, Ely, Tonopah, Wendover, West Wendover, and Winnemucca.The Central Basin and Range has a mosaic of xeric basins. The southern area of the basin has the communities of Palmdale, Victorville, and Palm Springs. Major roadways traversing the Great Basin include Interstate 80, Interstate 15, U.S. Route 6, U.S. Route 50, U.S. Route 93, U.S. Route 95 and U.S. Route 395, with the Nevada section of U.S. Route 50 nicknamed "The Loneliest Road in America." [ The Great Basin is traversed by several rail lines including the Union Pacific Railroad's Overland Route (Union Pacific Railroad) through Reno and Ogden, Feather River Route, Central Corridor and Los Angeles and Salt Lake Railroad. The Great Basin was once predominately inhabited by the Great Basin tribes. Ecology Although mostly within the North American Desert ecoregion, portions of the Great Basin extend into the Forested Mountain and Mediterranean California ecoregions. The semi-arid areas of the Forested Mountain ecoregion include the White Mountains and Inyo Mountains. Extending north of the 42nd parallel north, the Northern Basin and Range (ecoregion) has its southern border at the highest shoreline of the Pleistocene Lake Bonneville. The south edge of the Central Basin and Range ecoregion is in Nevada, north of the south edge of the Great Basin section. In phytogeography, the Great Basin is within the Great Basin (floristic) Province of the Madrean Region in southwestern North America. The floristic province and region are within the Holarctic Kingdom, of the northern Western Hemisphere.. Fauna Great Basin wildlife includes pronghorn, mule deer, mountain lion, and lagomorphs such as black-tailed jackrabbit and desert cottontail and the coyotes that prey on them. Packrats, kangaroo rats and other small rodents are also common, but these are predominantly nocturnal. Elk and bighorn sheep are present but uncommon. Small lizards such as the Great Basin fence lizard, longnose leopard lizard and horned lizard are common, especially in lower elevations. Rattlesnakes and gopher snakes are also present. The Inyo Mountains salamander is endangered. Shorebirds such as phalaropes and curlews can be found in wet areas. American white pelicans are common at Pyramid Lake. Golden eagles are also very common in the Great Basin. Mourning dove, western meadowlark, black-billed magpie, and common raven are other common bird species. Two endangered species of fish are found in Pyramid Lake: the Cui-ui sucker fish (endangered 1967) and the Lahontan cutthroat trout (threatened 1970). Large invertebrates include tarantulas (Aphonopelma genus) and Mormon crickets. Exotic species, including chukar, grey partridge, and Himalayan snowcock, have been successfully introduced to the Great Basin, although the latter has only thrived in the Ruby Mountains. Cheatgrass, an invasive species which was unintentionally introduced, forms a critical portion of their diets. Feral horses (mustangs) and wild burros are other highly reproductive, and ecosystem-controversial, alien species. Most of the Great Basin is open range and domestic cattle and sheep are widespread. Flora Utah juniper/single-leaf pinyon (southern regions) and mountain mahogany (northern regions) form open pinyon-juniper woodland on the slopes of most ranges. Stands of limber pine and Great Basin bristlecone pine (Pinus longaeva) can be found in some of the higher ranges (the Methuselah tree is nearly 5000 years old). In riparian areas with dependable water cottonwoods (Populus fremontii) and quaking aspen (Populus tremuloides) groves exist. Grasslands contain the native Great Basin wildrye. Hydrology The Great Basin Divide separates the Great Basin from the watersheds draining to the Pacific Ocean. The southernmost portion of the Great Basin is the watershed area of the Laguna Salada. The Great Basin's longest and largest river is the Bear River of 350 mi (560 km), and the largest single watershed is the Humboldt River drainage of roughly 17,000 sq mi (44,000 km 2 ). Most Great Basin precipitation is snow, and the precipitation that neither evaporates nor is extracted for human use will sink into groundwater aquifers, while evaporation of collected water occurs from geographic sinks. Lake Tahoe, North America's largest alpine lake, is part of the Great Basin's central Lahontan subregion. Great Basin named deserts include the Black Rock Desert, the Great Salt Lake Desert, the Sevier Desert, the Smoke Creek Desert, Nevada salt deserts in the Great Basin Province, the Mojave Desert, and part of the Sonoran Desert. 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