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3,� r-'ar:....�.""x .r' _ - 7- -`"r swg-�"RT��'�"' t`#"tom .,Y� �•�. z4. <br /> x <br /> E _ <br /> �.. 171-90 <br /> GEOLOGY <br /> a The study area is located near the northern boundary of the San Joaquin Valley, which is <br /> a northwest-southeast trending structural trough comprising the southern Iwo-thirds <br /> of the Central Valley, California (FIGURE 5). The San Joaquin Valley is bounded by the <br /> Sierra Nevada Mountains to the east, the Coastal Ranges to the west, and the Tehachapi <br /> and San Emlgdlo Mountains to the south. The San Joaquin Valley is bounded by the <br /> Sacramento Valley to the north, which is the northern structural extension of the <br /> Central Valley. <br /> -? The Sierra Nevada Complex, east of the San Joaquin Valley, is composed of crystalline, <br /> igneous and metamorph€c racks which include granite, gneiss, schist, and quartzite <br /> (Norris and Webb, 1976). The basement rock complex outcrops about thirty miles east <br /> of the study area. Valley fill sediments unconformable overlie the crystalline basement <br /> rocks in a westward thickening wedge. These sediments exceed 20,000 feet in thickness <br /> near the valley axis. Two general strat€graphic sequences are found in the valley fill <br /> deposits. These are divided in depositional origin and are, in decending order i) <br /> continental deposits, and 2) marine deposits. <br /> The site Is situated on the flat alluvial plains of the Central Valley formed by the build up <br /> of materials eroded from the Sierra Nevada Mountains and carried by the San Joaquin <br /> River. These materials predominantly consist of sand, silt, and clay. <br /> -- r ..... <br /> • 5 <br />