The Colorado River ('Aha Kwahwat in Mojave) is a river in the southwestern United States and northwestern Mexico, approximately 1,450 mi (2,330 km) long, draining a part of the arid regions on the western slope of the Rocky Mountains. The natural course of the river flows into the Gulf of California, but the heavy use of the river as an irrigation source for the Imperial Valley has desiccated the lower course of the river in Mexico such that it no longer consistently reaches the sea.

The Colorado River drains 242,900 sq mi (629,100 km²). Total flows of the river range from 4000 cubic feet per second (113 m³/s) in droughts to 1,000,000 ft³/s (28,000 m³/s) in severe floods. With the construction of massive power dams on the lower course of the river, floods of over 70,000 ft³/s (2000 m³/s) are rare. The mean flow of the total river before diversion is 22,000 ft³/s (620 m³/s). Historically the flow was much higher before water usage began in the basin.

Grand River

Until 1921, the section of the Colorado River from its headwaters in Rocky Mountain National Park to its confluence with the Green River in Utah was known as the "Grand River,"Early explorers identified the Gunnison River in Colorado as the headwaters of the Colorado River. The Grand River in Colorado was later identified as the headwaters of the river. Finally in 1916, E.C. LaRue, Chief Hydrologist of the United States Geological Survey, identified the Green River in Wyoming as the actual headwaters of the Colorado River. the origin of several now orphaned names including Grand Lake, Grand Valley, Grand Junction, Grand County, Colorado, and Grand County, Utah. Colorado U.S. Representative Edward T. Taylor petitioned the Congressional Committee on Interstate and Foreign Commerce to rename the Grand River as the Colorado River. On July 25, 1921 the name change was made official in House Joint Resolution 460 of the 66th Congress, over the objections of representatives from Wyoming and Utah and the United States Geological Survey which noted that the drainage basin of the Green River was more than 70% more extensive than that of the Grand River, although the Grand carried a slightly higher volume of water at its confluence with the Green.