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<br />.... <br />-..l <br />~ <br />.l.>. <br /> <br />in Lake Mohave is used for some reregulation of releases from Hoover Dam, for <br />meeting treaty requirements with Mexico. and for developing power head for the <br />production of electrical energy at Davis powerplant. The river flows through <br />a natural channel for about 10 miles below Davis Dam at which point the river <br />enters the broad Mohave valley 33 miles above the upper end of Lake Havasu. <br /> <br />Lake Havasu backs up behind Parker Dam for about 45 miles and serves as a <br />forebay from which the Metropolitan Water District of Southern California <br />pumps water into the Colorado River Aqueduct. Lake Havasu also serves as <br />forebay for the Central Arizona Project pumping plants and aqueducts. Lake <br />Havasu and Alamo Dam and Reservoir, on the Bill Williams River, are used to <br />control floods originating below Davis Dam and above Parker Dam. <br /> <br />Headgate Rock Dam, Palo Verde Diversion Dam, and Imperial Darn all serve <br />as diversion structures with practically no storage. Imperial Dam, located <br />some 150 miles downstream from Parker Dam, is the major diversion structure to <br />irrigation projects in the Imperial valley and Yuma areas. It diverts water <br />on the right bank to the All American canal, which delivers water to the Yuma <br />project in Arizona and California and Imperial and Coachella Valleys in <br />California. It diverts on the left bank to the Gila Gravity Main Canal. <br /> <br />The Senator Wash Dam, an offstream storage facility, also affords <br />regulation in the vicinity of Imperial Dam and assists in the delivery of <br />water to Mexico. This facility is used for pumpback storage and recreation. <br /> <br />The Morelos Dam is located just below the Northern International Boundary <br />with Mexico and is the last dam on the Colorado River. This small diversion <br />dam diverts water into the Alamo Canal which delivers water to northern Mexico. <br /> <br />o. Geology and Soils <br /> <br />The geology of the Colorado River Basin is highly varied. Igneous, <br />metamorphic, and sedimentary rock types are present and range in age from <br />approximately 625 million years old to recent alluvial deposits. Structural <br />features, including anticlines, domes, and faults, contribute to both the <br />topographic relief and the geohydrology of the region. <br /> <br />several of the sedimentary formations in the Basin were deposited in <br />marine or brackish water environments. Occurrences of bedded and disseminated <br />sodium chloride (halite) and calcium sulfate (gypsum) are observed as are <br />clays with high contents of exchangeable sodium and magnesium. <br /> <br />The soils of the Colorado River Basin closely resemble the geologic <br />formations from which they were derived. Residual soils derived from shale or <br />sandstone are generally shallow. These soils can contain appreciable soluble <br />mineral content due to residuum and secondary mineral formation from the <br />parent material. Upon weathering or irrigation, salts may accumulate on or <br />near the surface due to evaporation or consumptive use by plants. <br /> <br />Soils derived from alluvial materials vary in composition and thickness. <br />The deposits vary in origin and range from alluvial fans and terraces to <br />outwash plains and lake sediments. Some soils are composed of material <br />transported short distances. Soils that have been transported longer <br />distances are well mixed with respect to texture and composition. <br /> <br />1I-3 <br /> <br />- <br />