California water resource region

The California water resource region is one of 21 major geographic areas, or regions, in the first level of classification used by the United States Geological Survey in the United States hydrologic unit system, which is used to divide and sub-divide the United States into successively smaller hydrologic units. These geographic areas contain either the drainage area of a major river, or the combined drainage areas of a series of rivers.

The California region, which is listed with a 2-digit hydrologic unit code (HUC) of 18, has an approximate size of 168,579 sqmi, and consists of 10 subregions, which are listed with the 4-digit HUCs 1801 through 1810.

This region includes the drainage within the United States that ultimately discharges into the Pacific Ocean within the state of California; and those parts of the Great Basin (or other closed basins) that discharge into the state of California. Includes parts of California, Nevada, and Oregon.