The Colorado River 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.
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, 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.
The Colorado River’s source is La Poudre Pass Lake, located high in Rocky Mountain National Park, just west of the Continental Divide. Below Rocky Mountain National Park, the river flows through the Kawuneeche Valley and then flows through Grand Lake, the largest natural body of water in Colorado, before being dammed to create Shadow Mountain Reservoir. The river then flows into Lake Granby, another reservoir, and finally begins its journey to the Gulf of California where U.S. Highway 40 roughly parallels the river to the town of Kremmling, where it enters Gore Canyon. Most of the river’s tributaries within Colorado are small. However there are exceptions, such as the Gunnison and Roaring Fork Rivers, in which massive amounts of water flow. About a hundred miles later it meets the Eagle River in the town of Dotsero, Colorado and where I-70 parallels the river through Glenwood Canyon. The river then passes through the city of Glenwood Springs where it is joined by the swift flowing Roaring Fork River. West of Glenwood Springs, the Colorado runs through the Grand Valley and is joined by the Gunnison River in Grand Junction. From there it flows westward to the Utah border and Westwater Canyon. The Colorado here ranges from 200 to 1200 feet wide (60 to 370 m) and from 6 to 30 feet in depth (2 to 9 m) with occasional deeper areas.
Below the Black Canyon the river lessens in gradient and in its lower course flows in a broad sedimentary valley’s distinct estuarine plain upriver from Yuma, where it is joined by the Gila River. The channel through much of this region is bedded in a dike-like embankment lying above the floodplain over which the escaping water spills in time of flood. This dike cuts off the flow of the river to the remarkable low area in southern California known as the Salton Sink, Coachella Valley, or Imperial Valley. The Salton Sink is located below sea level; therefore, the descent from the river near Yuma is very much greater than the descent from Yuma to the gulf.
The lower course of the river, which forms the border between Baja California and Sonora, is essentially a trickle or a dry stream today due to use of the river as Imperial Valley’s irrigation source. Prior to the mid 20th century, the Colorado River Delta provided a rich estuarine marshland that is now essentially desiccated, but nonetheless is an important ecological resource.
he Colorado River basin is home to fourteen native species of fish. Four are endemic and endangered: Colorado pikeminnow (formerly Colorado squawfish), razorback sucker, bonytail chub, and humpback chub. The Upper Colorado River Endangered Fish Recovery Program is a controversial effort by the US Fish and Wildlife Service, in conjunction with the Arizona Game and Fish Department, the Colorado Division Of Wildlife, and the Utah Department Of Wildlife to recover these endangered fish.