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. . - . DESCRIPTION OF BASIN ~~ ~ ~ ~ through the Upper Basin to Lee Ferry. The Green River. its major trib- utary. rises in western Wyoming and discharges into the Colorado River In southeastern Utah--730 river miles south of its origin and 220 miles above Lee Ferry. The Green River drains 70 percent more area than the Colorado River above their junction but produces only about three- fourths as much water. The Gunnison and the San Juan are the other principal tributaries of the Upper Colorado River. The flows of the San Juan River are now controlled by the Navajo Dam. the Green River by Fontenelle and Flaming Gorge Dams, and the Gunn- ison River by the Curecanti Unit Dams. Glen Canyon Dam is the only major dam on the main stem of the Colorado above Lee Ferry. but it will permit control of almost all flows leaving the Upper Basin. The flow at various points in streams in the Colorado River Basin for the 1941-74 period is given in Tables I through 17. The records of flow depict the characteristic wide fluctuations from month-to-month and the considerable variation from year-to-year. The storage reservoirs now level out some of the fluctuations in the reaches below the dam. The natural drainage area of the lower Colorado River below Lee Ferry and above Imperial Dam is about 75.100 square miles. This section of the river is now largely controlled by a series of storage and diver- sion dams starting with Hoover Dam and ending at Imperial Dam. At the present time there is no significant storage on the main river or on the tributaries between Glen Canyon Dam and Lake }1ead. The intervening tributary inflow is erratic but amounts to almost enough to offset the evaporation from Lake ~ead. Lake Mead provides most of the storage and regulation in the Lower Colorado River Basin with the water being stored for irrigation and municipal and industrial uses, generation of electrical power, and other beneficial uses. Lake Mohave, the reservoir formed by Davis Dam, backs water at high stages about 67 miles upstream to the tailrace of Hoover Powerplant. Storage in Lake Mohave is used for some reregulation of releases from Hoover Dam, for meeting treaty requirements with Mexico, and for devel- oping power head for the production of electrical energy at Davis Powerplant. The river flows through a natural channel for about 10 miles below Davis Dam at which point the river enters the broad Xohave Valley 33 miles above the upper end of Lake Havasu. Lake Havasu backs up behind Parker Dam for about 45 miles and cov- ers about 25,000 acres. Lake Havasu serves as a forebay from which the Xetropolitan Water District of Southern California pumps water into the 8