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<br />" <br /> <br />, <br /> <br />. <br /> <br />. <br /> <br />type of erosion reaches its culmination in the Grand Canyon where the Colorado <br />River has cut through all of the sedimentary rocks down to the oldest Archean <br />granites. <br /> <br />The Lower Basin is characterized by,broad, flat valleys separated by low <br />mountain ranges. These valleys are filled by large accumulations of alluvial <br />deposits. Sediment removed by constant erosion of the upper areas was <br />deposited in Arizona, California, and Mexico and now forms the great delta of <br />the Colorado River. <br /> <br />Soil s <br /> <br />The soils of the Colorado River Basin closely resemble the geologic formations <br />of their origin. Only in limited areas at the higher elevations has the <br />precipitation leached the soil mass of its soluble constituents. Over most <br />of the area both residual and transported soils are basic in reaction and <br />well supplied with carbonates with normal or mature soils exhibiting a <br />distinct horizon of carbonate accumulation. Soils formed in this area are in <br />orders of Entisols, Aridisols, Mollisols, Alfisols, Saline and Sodic. <br /> <br />Extensive areas of Eolian deposits occur in parts of the basin, principally <br />in southwestern Colorado. The uniformly textured soils are reddish brown in <br />color and have no resemblance to either the underlying formations or adjacent <br />areas. These are ~xcellent agricultural soils, but in many areas topography <br />makes agriculture difficult. <br /> <br />Hydro logy <br /> <br />The Colorado River begins where peaks rise more than 14,000 feet high in the <br />northwest portion of Colorado's Rocky Mountain National Park. <br /> <br />The Green River, the major tributary, rises in western Wyoming and discharges <br />into the Colorado River in southeastern Utah. The Green River drains 70 <br />percent more area than the Colorado River above their junction but produces <br />only about three-fourths as much water. The Gunnison and the San Juan are <br />the other principal tributaries of the Upper Colorado River. <br /> <br />The stream flow of the San Juan River is now controlled by the Navajo Dam, <br />the Green River by Fontene11e and Flaming Gorge Dams, and the Gunnison River <br />by the Curecanti Unit Dams. Glen Canyon Dam controls a bulk of the stream <br />flows from the Colorado River Upper Basin. <br /> <br />The natural drainage area of the lower Colorado River below Lee Ferry and <br />above Imperial Dam is about 75,100 square miles (195,000 km2). This section <br />of the river is now largely controlled by a series of storage and diversion <br />dams starting with Hoover Dam and ending at Imperial Dam. <br /> <br />Lake Mead provides most of the storage and regulation in the Lower Colorado <br />River Basin with the water being stored for irrigation and municipal and <br />industrial uses, generation of electrical power, flood control, and other <br />beneficial uses. <br /> <br />" <br /> <br />6 <br />