Basins Nevada The U.S. Geological Survey (USGS) and the Nevada Division of Water Resources, Department of Conservation and Natural Resources, have divided the state into discrete hydrologic units for water planning and management purposes. These have been identified as 232 Hydrographic Areas (256 areas and sub-areas, combined) within 14 major Hydrographic Regions or Basins. These 14 Nevada Hydrographic Regions (Basins), along with the approximate surface areas (Nevada only), counties of coverage, extension into adjoining states, and number of hydrographic areas and sub-areas are: 1 Northwest Region – Covers 3,052 square miles (7,905 square kilometers or 1,953,280 acres) of northern Washoe and Humboldt counties and encompasses 16 hydrographic areas, also extends into the State of California to the west and the State of Oregon to the north, 2 Black Rock Desert Region – Covers 8,632 square miles (22,357 square kilometers or 5,524,480 acres) of parts of Washoe, Humboldt, and Pershing counties and includes 17 valleys (hydrographic areas), two of which are divided into two hydrographic sub-areas each, also extends into the State of California to the west and the State of Oregon to the north, 3 Snake River Basin – Covers 5,230 square miles (13,546 square kilometers or 3,347,200 acres) in parts of Elko and Humboldt counties to include eight hydrographic areas, also extends into the states of Oregon and Idaho to the north and the State of Utah to the east, 4 Humboldt River Basin – Covers over 16,843 square miles (43,623 square kilometers or 10,779,520 acres) in parts of eight counties – Elko, White Pine, Eureka, Humboldt, Lander, Nye, Pershing, and Churchill – and the largest stream (Humboldt River) wholly within Nevada. This basin contains 34 hydrographic areas and one hydrographic sub-area, this basin is one of only two that are wholly contained within the State of Nevada, 5 West Central Region – Covers 1,656 square miles (4,289 square kilometers or 1,059,840 acres) and includes parts of Pershing, Lyon, and Churchill counties and comprises five hydrographic areas, this basin is one of only two that are wholly contained within the State of Nevada, 6 Truckee River Basin – Encompasses 2,300 square miles (5,957 square kilometers or 1,472,000 acres) containing parts of Washoe, Pershing, Churchill, Lyon, Douglas, Carson City, and Storey counties comprising 12 hydrographic areas, has its origin to the west in the State of California, 7 Western Region – Covers 602 square miles (1,559 square kilometers or 385,280 acres) and is wholly contained in Washoe County and contains nine valleys (hydrographic areas) one of which is divided into two sub-areas and another divided into one hydrographic sub-area, also extends to the west into the State of California, 8 Carson River Basin – Covers 3,519 square miles (9,114 square kilometers or 2,252,160 acres) and includes parts of six counties – Douglas, Carson City, Lyon, Storey, Churchill, and Pershing – containing five hydrographic areas and one hydrographic sub-area along the Carson River and its tributaries, has its origin to the west in the State of California, 9 Walker River Basin – Covers 3,046 square miles (7,889 square kilometers or 1,949,440 acres) of Mineral, Lyon, and Douglas counties (and a very small portion of Churchill County) including five hydrographic areas, one of which has been divided into three hydrographic sub-areas, has its origin to the west in the State of California, 10 Central Region – By far the largest hydrographic region in Nevada covering 46,783 square miles (121,167 square kilometers or 29,941,120 acres) in 13 counties – Nye, Elko, White Pine, Lincoln, Clark, Humboldt, Pershing, Churchill, Lander, Eureka, Lyon, Mineral, and Esmeralda. This region includes 78 valleys (hydrographic areas), 10 of which are divided into two hydrographic sub-areas and one into three hydrographic sub-areas, extends to the south and west into the State of California, 11 Great Salt Lake Basin – Covers 3,807 square miles (9,860 square kilometers or 2,436,480 acres) of the easternmost portions of Elko, White Pine, and Lincoln counties. It consists of eight hydrographic areas, one of which is divided into four hydrographic sub-areas, extends to the east into the State of Utah, 12 Escalante Desert Basin – This basin covers a large area in Utah but only a very small part of it is in Lincoln County – 106 square miles (275 square kilometers or 67,480 acres) – and is made up of only one hydrographic area, extends to the east into the State of Utah, 13 Colorado River Basin – Covers 12,376 square miles (32,054 square kilometers or 7,920,640 acres) including parts of Clark, Lincoln, Nye, and White Pine counties and is divided into 27 hydrographic areas, extends to the south into the State of California, borders the Colorado River to the east and south, and extends into the states of Arizona and Utah to the east, 14 Death Valley Basin – Covers 2,593 square miles (6,716 square kilometers or 1,659,520 acres) of Nye and Esmeralda counties including eight hydrographic areas, one of which has been divided into two hydrographic sub-areas, extends into the State of California to the south and west. A listing of Nevada’s Hydrographic Regions, Areas and Sub-Areas is presented in Appendix A-1 (hydrographic regions, areas and sub-areas), Appendix A-2 (listed sequentially by area number) Appendix A-3 (listed alphabetically by area name), and Appendix A-4 (listed alphabetically by principal Nevada county(ies) in which located).