The Colorado River rises high in the snow-capped Rocky Mountains of north central Colorado, flows nearly 1,400 miles southwest, and empties into the Gulf of California in Mexico far to the south. It is the second longest river in the United States outside the Mississippi River system. This mighty river has gouged the rock of the mesas into gorges and chasms, most spectacular of which is the world-famous Grand Canyon in Arizona, a titanic cleft over 200 miles long, as much as 12 miles wide, and a mile deep.

The Colorado River drains a vast area of 244,000 square miles, 242,000 square miles in this country-onetwelfth of the area of Continental United States-and 2,000 square miles in northern Mexico. The basin from Wyoming to below the Mexican border is some 900 miles long and varies in width from about 300 miles in the upper section to 500 miles in the lower section. It is bounded on the north and east by the Continental Divide in the Rocky Mountains, on the west by the Wasatch Range, and on the southwest by the San Jacinto Mountains, a range of the Sierra Nevada. Tributaries extend into seven of the large Western States including Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.

The Salton Sea Basin, an additional area of 7,800 square miles which includes the Coachella and Imperial Valleys in southeastern California, is discussed as part of the Lower Colorado River Basin. It is, however, to be distinguished from other lower Colorado River areas because whatever Colorado River water reaches it cannot return by gravity flow to the parent stream.

Physical Characteristics

The upper or northern portion of the Colorado River Basin in Wyoming and Colorado is a mountainous plateau, 5,000 to 8,000 feet in altitude, marked by broad rolling valleys, deep canyons, and intersecting mountain ranges. Hundreds of peaks in these mountain chains rise to more than 13,000 feet above sea level and many exceed 14,000 feet. There are many picturesque mountain lakes in these headwater sections. The southern por

tion of the basin is studded with rugged mountain peaks interspersed with broad, level, alluvial valleys and rolling plateaus.

The main stream and its principal tributaries in Colorado flow, for the most part, in deep canyons. The Green River, primary tributary of the Colorado River, flows in similar canyons in Wyoming, Colorado, and Utah and its chief tributaries, Yampa and White Rivers from the east, and Duchesne, Price, and San Rafael Rivers from the west, flow through rolling hills and canyons to reach the Green.

The San Juan River, a large tributary of the Colorado River from the east, drains mountain slopes and plateaus in southwestern Colorado, northwestern New Mexico, and northern Arizona and flows through a formidable canyon in southeastern Utah, joining the Colorado in Glen Canyon. The Glen Canyon section of the main stream and tributaries thereto are in deep canyons, draining a series of plateaus and mesas.

Below Glen Canyon is the awesome Grand Canyon where the Colorado has carved an unparalleled chasm. This canyon yawns above an inner gorge, rising in gigantic cliff-steps to the Colorado plateau, a mile above the stream bed. This great central plateau is a rolling expanse of brightly hued crags and cliffs, huge canyons, painted deserts, and extensive almost inaccessible barren areas. Elevations on the mesas of the plateau section generally range from 4,000 to 6,000 feet. The principal tributaries in this section are the Little Colorado River on the east and the Virgin River on the west.

Emerging from the canyon country at the southeast corner of Nevada, the Colorado River courses through broad valleys bordered by mesas. The Gila River, main tributary in this section, rises in the mountainous region of southwestern New Mexico and drains most of southern Arizona.

Southwest of the Gila Basin the Colorado River continues through its great delta area to the Gulf of California.

Physical characteristics suggest seven main divisions of the Colorado River Basin in the United States, three in the upper basin, or the drainage area above Lee Ferry, Arizona, and four in the lower basin, or the drainage