Colorado River - Course

Course

The Colorado rises at La Poudre Pass east of the Never Summer Mountains in the Colorado Rockies, about 60 miles (97 km) northwest of Denver. The river runs south before turning west below Grand Lake, the largest natural lake in the state. After passing Kremmling it cuts a series of narrow canyons, including Gore, Glenwood, and De Beque. The Colorado emerges from the mountains at the Grand Valley, where it is joined by the Gunnison River before arcing northwest into desert Utah. Carving its way southwest across the Colorado Plateau, the Colorado forms Cataract Canyon and other gorges and receives its principal tributary, the Green River, before flowing into Lake Powell, a reservoir formed by the Glen Canyon Dam in Arizona nearly 200 miles (320 km) downstream.

The Colorado passes Lee's Ferry in Arizona, the official dividing point of the Upper and Lower Colorado River Basins, before swinging south then west through the Grand Canyon. Below Lake Mead – the largest man-made lake in the U.S., formed by Hoover Dam at the junction of Arizona, Nevada and Utah – the river turns sharply south. As it enters the Lower Colorado River Valley the Colorado delineates much of the Arizona–Nevada border, the entirety of the Arizona–California border, and is impounded by a series of dams, including Imperial Dam, where most of its flow is diverted into the All-American Canal to irrigate the Imperial Valley in California. Below the confluence with the Gila River the Colorado forms a short stretch of the Mexico–United States border before passing entirely into Mexico. It empties into the Gulf of California via a large estuary, the Colorado River Delta, roughly 75 miles (121 km) south of Yuma, Arizona.

With its headwaters at 10,184 feet (3,104 m), the Colorado River loses nearly two miles in elevation by the time it reaches the Gulf. Most of the Colorado above Lake Mead is a swift-moving whitewater river, with the exception of the region around Grand Junction, Colorado, where it exhibits braided characteristics, and the marshy Kawuneeche Valley near the headwaters. The lower river between Hoover Dam and the international border is generally a slow-moving, meandering stream. Much of the upper Colorado ranges from 200 to 500 feet (61 to 150 m) wide, compared with 500 to 1,000 feet (150 to 300 m) for the lower river, with an average depth of 10 to 30 feet (3.0 to 9.1 m). Some parts of the river are as shallow as 2 to 8 feet (0.61 to 2.4 m) in the lower course in dewatered sections near Yuma, and one notable section in the Grand Canyon reaches up to 110 feet (34 m) in depth.

The river was characterized by sweeping meanders, sandbars and islands that were subject to frequent course changes before channelization of the lower Colorado in the 20th century. Joseph C. Ives, who surveyed the lower river in 1861, wrote that "the shifting of the channel, the banks, the islands, the bars is so continual and rapid that a detailed description, derived from the experiences of one trip, would be found incorrect, not only during the subsequent year, but perhaps in the course of a week, or even a day." The delta and estuary of the Colorado River were once also subjected to a major tidal bore that has almost disappeared with reductions in river flow and some dredging of the estuary channel. The first historical record of the tidal bore was that made by the Croatian missionary in Spanish service Father Ferdinand Konščak on 18 July 1746. During spring tide conditions, the tidal bore formed in the estuary about Montague Island in Baja California and propagated upstream. It was locally called El Burro or burro.