The New International Encyclopædia/Colorado River

COLORADO RIVER. A large river flowing through the plateau region of the southwestern United States. It is formed in the southwestern part of Utah, by the junction of the Green River from the north and the Grand from the northeast, the former rising in southwestern Wyoming and the latter in the north central part of Colorado. Both of these headstreams receive numerous tributaries from the well-watered regions of the Rocky Mountains. Below their junction, the Colorado passes through what is in some respects the most remarkable region on the earth, not only for its natural scenery, but also for the great interest which it possesses for geologists, as it gives on a grand scale the clearest exemplifications of the action of erosive forces in shaping the contour of the land. In the Eocene epoch the whole region of Arizona, Utah, and Nevada was subjected to a vast upheaval, and what was formerly the bottom of the ocean was raised to a height of more than 10,000 feet above sea-level. This region, consisting chiefly of horizontal strata of the Paleozoic and Mesozoic systems, was subjected to extensive denudation by wind and water, and again to successive upheavals accompanied by volcanic action. In the northwestern part the strata were faulted into huge blocks, running north and south, giving the present shape to the mountains of Nevada. The result of the uplifting and erosion was the washing away of the weaker and softer strata, especially to the west of the present course of the Colorado, while those rocks that were protected by harder layers were left standing as extensive plateaus with precipitous escarpments. In some places lavas had been thrust up through the strata by volcanic action, and these localities are now marked by the isolated mesas so characteristic of the country. Since this region is almost or quite rainless below an elevation of 8000 feet, denudation proceeds slowly except along the river-courses, where chasms or cañons are cut deeply into the rock foundations. Such is the case with the Colorado and all the tributaries from its headwaters to the great escarpment called the Grand Wash, on the western boundary of Arizona.

The largest and deepest of these is the famous Grand Cañon, where the Colorado cuts through the Kaibab and Unikaret plateaus, from 7000 to 9000 feet high, in the northern part of Arizona. The cañon is five to six miles wide at the top and 5000 to 6000 feet deep, falling in several successive escarpments, indicating pauses in the upheaval of the plateau. In the middle is the narrow and gloomy cañon proper, with a sheer precipitous depth of 2000 to 3000 feet, at the bottom of which rushes the river. The length of the Grand Cañon is over 200 miles. After the river emerges from the cañon it turns abruptly south, and, forming the western boundary of Arizona, it flows through a low desert region, receiving almost no tributaries, and diminishing in volume by evaporation and absorption. Leaving United States territory near its mouth, it empties into the Gulf of California. The total length of the river is about 900 miles, and with the Green, 2000 miles. It is navigable for light steamers for several hundred miles from its mouth, but navigation is much impeded by rocks and sand-bars, as well as by the ever-changing volume of its water and the shifting of its bed. The river was discovered in 1540 by Fernando Alarcón, and the perilous descent through the cañon was first made by James White in 1867. Valuable additions to geological science have resulted from expeditions into the cañon, conducted by the United States Geological Survey. See J. W. Powell, Exploration of the Colorado River of the West and its Tributaries; and Dutton, Tertiary History of the Grand Cañon of the Colorado, Monograph II., United States Geological Survey, 1882.