COLORADO

See also:

• RIVER

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 head-waters 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 15oo 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 6o 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 Grand Canyon (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, to the west of which, in Mexico, is Laguna Maquata (or Salada), lying in the so-called Pattie Basin, which was formerly a part of the Gulf of California, and which is frequently partially flooded (like Coahuila Valley) by the delta waters of the Colorado . Of the total length of the Colorado, about 2200 m., 500 M. or more from the mouth are navigable by light steamers, but channel obstacles make all navigation difficult at low water, and impossible about half the year above Mojave . The whole area drained by the river and its tributaries is about 225,000 sq. m.; and it has been estimated by Major J . W . Powell that in its drainage basin there are fully 200,000 sq. m. that have been degraded on an average 6000 ft . It is still a powerful eroding stream in the canyon portion, and its course below the canyons has a shifting bed much obstructed by bars built of sediment carried from the upper course . The desert country toward the mouth is largely a sandy or gravelly aggradation plain of the river .

The

regular floods are in May and June . Others, due to rains, are rare . The rise of the water at such times is extraordinarily rapid . Enormous drift is left in the canyons 30 or 40 ft. above the normal level . The valley near Yuma is many miles wide, frequently inundated, and remark-ably fertile; it is often called the " Nile of America " from its resemblance in climate, fertility, overflows and crops . These alluvial plains are covered with a dense growth of mesquite, cottonwood, willow, arrowwood, quelite and wild hemp . Irrigation is essential to regular agriculture . There is a fine delta in the gulf . The Colorado is remarkable for exceedingly high tides at its mouth and for destructive bores . In 1540, the second year that Spaniards entered Arizona, they discovered the Colorado . Hernando de Alarcon co-operating with F . V. de Coronado, explored with ships the Gulf of California and sailed up the lower river; Melchior Diaz, marching along the shores of the gulf, likewise reached the river; and Captain Garcia Lopez de Cardenas, marching from Zuni, reached the Grand Canyon, but could not descend its walls .

In 1604 Juan de 'Dilate crossed Arizona from New Mexico and descended the

Santa Maria, Bill Williams and Colorado to the gulf . The name Colorado was first applied to the present Colorado Chiquito, and probably about 163o to the Colorado of to-day . But up to 1869 great portions of the river were still unknown . James White, a miner, in 1867, told a picturesque story (not generally accepted as true) of making the passage of the Grand Canyon on the river . In 1869, and in later expeditions, the feat was accomplished by Major J . W . Powell . There have been since then repeated explorations and scientific studies . See C . E . Dutton, " Tertiary History of the Grand Canyon," U.S . Geological Survey, Monograph II .

(1882); J . W . Powell, Exploration of the Colorado River (

Washington, 1875), and Canyons of the Colorado (Meadville, Pa . 1895) ; F . S . Dellenbaugh, Romance of the Colorado River (New York, 1902), and Canyon Voyage (1908); G . W . James, Wonders of the Colorado Desert (2 vols., Boston, 1906) .