The Great Basin is the largest area of contiguous endorheic watersheds in North America having no connection to the ocean. It spans sections of western Wyoming, southern Idaho, much of northwest Utah, nearly all of Nevada, areas in southwest Oregon, both eastern and southern California and the north area of the Mexican state of Baja California.

This hydrographic region spans numerous physiographic divisions, biomes, ecoregions, and several desert areas.

Biomes include: Alpine communities; Montane communities; Pinyon-Juniper communities; Riparian communities; Salt deserts; Shadescale-dominated saline basins; Lahontan and Tonopah playas; Lahontan salt shrub basin; Lahontan sagebrush slopes; Lahontan uplands; upper Humboldt plain, Carbonate sagebrush valleys; central Nevada high valleys; central Nevada mid-slope wood and brushlands; Central Nevada bald mountains; and the Tonopah basin

In contrast, the Great Basin Desert is a smaller area defined by plant and animal communities, and which boundaries do approximate the hydrographic Great Basin area.

However, the Great Basin Desert excludes the southern panhandle of the Great Basin hydrographic area, the area of the endoheic region which extends southward into the Mojave Desert through the bottom of California and into Baja California.

. The great basin borders: Northern Basin and Range ecoregion (2G); Sierra Nevada ecoregion (1N); Wasatch and Uinta Mountains ecoregion (3G); Colorado Plateau ecoregion (2I); and Mojave Basin ecoregion (2K)

190,000 square miles,

The total Great Basin is more than 209,000 square miles.

Bear River, Humbolt river, Mojave river, Owens river, Sevier river

Amargosa river, American Fork, Chewaucan River

Endorheic desert and xeric shrublands