The purpose of this report is to present the facts regarding available water supply and all known dam sites on Colorado River between Cataract Canyon, Utah, and Parker, Ariz., and to show the relative value of these dam sites. To determine the relative value of the dam sites, a comprehensive plan of development for Colorado River below the mouth of Green River is presented that will provide for the maximum practicable utilization of the potential power, maximum preservation of water for irrigation, effective elimination of the flood menace, and adequate solution of the silt problem. This plan, which is preliminary and is offered by the writer to show the basis for his conclusions relative to flood control, irrigation, power development, and silt storage, contemplates the construction of 13 dams making available 3,383 feet of head for the development of power and a maximum of 42,000,000 acre-feet of storage capacity for the control of floods, equalization of flow, and storage of silt.