What is the Colorado River?

The Colorado River is a major river of the American Southwest, flowing about 1,450 miles from the Rocky Mountains of Colorado to the Gulf of California in Mexico, draining a basin of about 246,000 square miles across seven U.S. states (Colorado, Wyoming, Utah, New Mexico, Arizona, Nevada, California) and two Mexican states (Baja California, Sonora). The river rises in La Poudre Pass in Rocky Mountain National Park, Colorado at an elevation of 10,184 feet. It flows southwest through the spectacular canyon country of western Colorado, eastern Utah, and northern Arizona, then west and south to the U.S.-Mexico border near Yuma, Arizona, and finally through Mexico to the Gulf of California (Sea of Cortez).

The Colorado is famous for the Grand Canyon, which it carved over the past five to six million years through the Colorado Plateau in northern Arizona. The Grand Canyon is about 277 miles long, up to 18 miles wide, and as much as 6,000 feet deep, exposing rock layers up to 1.8 billion years old. Other major canyons on the river include Black Canyon of the Gunnison, Glen Canyon (now mostly drowned by Lake Powell), and Marble Canyon.

Major dams have transformed the river. Hoover Dam, completed in 1936 on the Arizona-Nevada border, is 726 feet tall and creates Lake Mead, the largest reservoir in the United States by capacity. Glen Canyon Dam, completed in 1966 in northern Arizona, is 710 feet tall and creates Lake Powell, the second largest reservoir. Other major dams include Davis, Parker, Imperial, and Laguna in the lower river. These dams provide water and electricity to about 40 million people across the Southwest, including major cities like Las Vegas, Phoenix, Tucson, Los Angeles, San Diego, and the Imperial Valley agricultural region. About 80 percent of Colorado River water is used for agriculture.

The Colorado River Compact of November 24, 1922 divided water among the seven basin states, with the Upper Basin (Colorado, Utah, New Mexico, Wyoming) allocated 7.5 million acre-feet and the Lower Basin (Arizona, California, Nevada) another 7.5 million acre-feet. Mexico received 1.5 million acre-feet under the 1944 Treaty. The Compact's allocation has proven optimistic; actual flows in recent decades have been about 12 million acre-feet, less than the 16.5 million acre-feet promised. Climate change and persistent drought have intensified water shortages, with Lake Mead reaching record low levels in the 2020s. The river rarely reaches the Gulf of California now because so much water is withdrawn upstream.

Indigenous nations including the Hualapai, Havasupai, Navajo, Hopi, Mohave, Quechan, Cocopah, and Chemehuevi have lived along the Colorado for centuries and continue to depend on it.