The Lower Colorado 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 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 Lower Colorado region, which is listed with a 2-digit hydrologic unit code (HUC) of 15, has an approximate size of 140,146 square miles (362,980 square kilometers), and consists of 8 subregions, which are listed with the 4-digit HUCs 1501 through 1508.This region includes the drainage within the United States of: (a) the Colorado River Basin below the Lee Ferry compact point which is one mile below the mouth of the Paria River; (b) streams that originate within the United States and ultimately discharge into the Gulf of California; and (c) the Animas Valley, Willcox Playa, and other smaller closed basins. Includes parts of Arizona, California, Nevada, New Mexico, and Utah.