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   COLORADO RIVER, a stream in the south of the Argentine Republic. It has its sources on the eastern slopes of the Andes in the lat. of the Chilean volcano Tinguiririca (about 34° 48′ S.), and pursues a general E.S.E. course to the Atlantic, where it discharges through several channels of a delta extending from lat. 39° 30′ to 39° 30′ S. Its total length is about 620 m., of which about 200 m. from the coast up to Pichemahuida is navigable for vessels of 7 ft. draft. It has been usually described as being formed by the confluence of the Grande and Barrancas, but as the latter is only a small stream compared with the Grande it is better described as a tributary, and the Grande as a part of the main river under another name. After leaving the vicinity of the Andes the Colorado flows through a barren, arid territory and receives no tributary of note except the Curaco, which has its sources in the Pampa territory and is considered to be part of the ancient outlet of the now closed lacustrine basin of southern Mendoza. The bottom lands of the Colorado in its course across Patagonia are fertile and wooded, but their area is too limited to support more than a small, scattered population.  COLORADO RIVER, a stream in the south-west of the United States of America, draining a part of the high and arid plateau between the Rocky mountains and the Sierra Nevada in California. The light rainfall scarcely suffices over much of the river’s course to make good the loss by evaporation from the waters drained from mountain snows at its source. Its headwaters are known as the Green river, which rises in north-west Wyoming and after a course of some 700 m. due south unites in south-east Utah with the Grand river, flowing down from Colorado, to form the main trunk of the Colorado proper. The Green cuts its way through the Uinta mountains of Wyoming; then flowing intermittently in the open, it crosses successive uplifts in a series of deep gorges, and flows finally at the foot of canyon walls 1500 ft. high near its junction with the Grand.

The Colorado in its course below the junction has formed a region that is one of the most wonderful of the world, not only for its unique and magnificent scenery, but also because it affords the most remarkable example known of the work of differential weathering and erosion by wind and water and the exposure of geologic strata on an enormous scale. Above the Paria the river flows through scenery comparatively tame until it reaches the plateau of the Marble Canyon, some 60 m. in length. The walls here are at first only a few score of feet in height, but increase rapidly to almost 5000 ft. At its southern end is the Little Colorado. Above this point eleven rivers with steep mountain gradients have joined either the Green or the Grand or their united system. The Little Colorado has cut a trench 1800 ft. deep into the plateau in the last 27 m. as it approaches the Colorado, and empties into it 2625 ft. above the sea. Here the Colorado turns abruptly west directly athwart the folds and fault line of the plateau, through the (q.v.) of the Colorado, which is 217 m. long and from 4 to 20 m. wide between the upper cliffs. The walls, 4000 to 6000 ft. high, drop in successive escarpments of 500 to 1600 ft., banded in splendid colours, toward the gloomy narrow gorge of the present river. Below the confluence of the Virgin river of Nevada the Colorado abruptly turns again, this time southward, and flows as the boundary between Arizona and California and in part between Arizona and Nevada, and then through Mexican territory, some 450 m. farther to the Gulf of California. Below the Black Canyon the river lessens in gradient, and in its lower course flows in a broad sedimentary valley—a distinct estuarine plain extending northward beyond Yuma—and the channel through much of this region is bedded in a dyke-like embankment lying above the flood-plain over which the escaping water spills in time of flood. This dyke cuts off the flow of the river to the remarkable low area in southern California known as the Salton Sink, or Coahuila Valley, the descent to which from the river near Yuma is very much greater than the fall in the actual river-bed from Yuma to the gulf. In the autumn of 1904, the diversion flow from the river into a canal heading in Mexican territory a few miles below Yuma, and intended for irrigation of California south of the Sink, escaped control, and the river, taking the canal as a new channel, recreated in California a great inland sea—to the bed of which it had frequently been turned formerly, for example, in 1884 and 1891—and for a time practically abandoned its former course through Mexican territory to the Gulf of California. But it was effectively dammed in the early part of 1907 and returned to its normal course, from which, however, there was still much leakage to Salton Sea; in July 1907 the permanent dam was completed. From the Black Canyon to the sea the Colorado normally flows through a desert-like basin,