The Great Basin overlaps four different deserts: portions of the hot Mojave and Colorado (a region within the Sonoran desert) Deserts to the south, and the cold Great Basin and Oregon High Deserts in the north. The ecological boundaries and divisions in the Great Basin are unclear. The hydrographic Great Basin contains multiple deserts and ecoregions, each with its own distinctive set of flora and fauna. Great Basin snowstorm in the Snake Valley of Utah and Nevada Lake Tahoe, North America's largest alpine lake, is part of the Great Basin's central Lahontan subregion. 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. 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). The southernmost portion of the Great Basin is the watershed area of the Laguna Salada. The Great Basin Divide separates the Great Basin from the watersheds draining to the Pacific Ocean. The Salton Sink is another closed basin within the Great Basin. The Great Salt Lake, Pyramid Lake, and the Humboldt Sink are a few of the 'drains' in the Great Basin. The term 'Great Basin' is slightly misleading the region comprises many small basins. The Great Basin includes most of Nevada, half of Utah, substantial portions of Oregon and California, and small areas of Idaho, Wyoming, and Baja California, Mexico.

The region is bounded by the Wasatch Mountains to the east, the Sierra Nevada and Cascade Ranges to the west, and the Snake River Basin to the north. As observed by Fremont, creeks, streams, or rivers find no outlet to either the Gulf of Mexico or the Pacific Ocean. However, since the advent of the Los Angeles Aqueduct, for over a century, a large portion of water has been transported out of the area, leaving the landscape permanently altered. All precipitation in the region evaporated, sank underground or flowed into lakes (mostly saline). The hydrographic Great Basin is a 209,162-square-mile (541,730 km 2) area that once drained internally. The Tule Valley watershed and the House Range ( Notch Peak) are part of the Great Basin's Great Salt Lake hydrologic unit The culture area covers approximately 400,000 sq mi (1,000,000 km 2), or just less than twice the area of the hydrographic Great Basin. The Great Basin Culture Area or indigenous peoples of the Great Basin is a cultural classification of indigenous peoples of the Americas and a cultural region located between the Rocky Mountains and the Sierra Nevada. The 'section' is somewhat larger than the hydrographic definition. The United States Geological Survey adapted Fenneman's scheme in their Physiographic division of the United States. The Great Basin physiographic section is a geographic division of the Basin and Range Province defined by Nevin Fenneman in 1931. The Great Basin Floristic Province was defined by botanist Armen Takhtajan to extend well beyond the boundaries of the hydrographically defined Great Basin: it includes the Snake River Plain, the Colorado Plateau, the Uinta Basin, and parts of Arizona north of the Mogollon Rim. The Great Basin Desert is defined by plant and animal communities, and, according to the National Park Service, its boundaries approximate the hydrographic Great Basin but exclude the southern ' panhandle'.

The other definitions yield not only different geographical boundaries of 'Great Basin' regions but regional borders that vary from source to source.

: 8–9 The hydrographic definition is the most commonly used, and is the only one with a definitive border. Walker as well as his own travels, recognized the hydrographic nature of the landform as 'having no connection to the ocean'. Frémont, who, based on information gleaned from Joseph R. : 34 The name was originally coined by John C. The term 'Great Basin' is applied to hydrographic, : 11 biological, floristic, : 21 physiographic, : 14 topographic, and ethnographic geographic areas. The hydrographic Great Basin (magenta outline), distinguished from the Great Basin Desert (black), and the Basin and Range Geological Province (teal).

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