The Souris–Red–Rainy 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.[1][2]
The Souris–Red–Rainy Region, which is listed with a 2-digit hydrologic unit code (HUC) of 09, has an approximate size of 90,759 square miles (235,060 square kilometers), and consists of 3 subregions, which are listed with the 4-digit HUC codes of 0901 through 0903.