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Former Discovery Chevrolet June 5, 1998 Tracy,California Corrective Action Plan == range of uplifted intrusive granitic rocks and remnant metamorphic rocks of pre-Tertiary age. These rocks form an asymmetrical fault block that dips gently to the west and comprise the basement complex beneath the Central Valley. The Coast Ranges border the Central Valley on the west and consist mostly of complexly folded and faulted consolidated marine and nonmarine sedimentary rocks of Jurassic, Cretaceous, and Tertiary age. These rocks dip eastward toward the Central Valley and overlie the basement complex. The Great Valley geomorphic province consists of two broad alluvial valleys, the Sacramento Valley in the north and the San Joaquin Valley in the south. These two valleys meet in the area of the inland delta that marks the confluence of the San Joaquin River with the Sacramento River. The Central Valley is flanked by alluvial fans deposited at the foot of the Coast Ranges to the west and the Sierra Nevada Mountains to the east. Unconsolidated deposits comprise the upper stratigraphic sequence of the Central Valley. These deposits have been mapped as continental and lacustrine deposits of Holocene to Miocene in age. The unconsolidated deposits are underlain by consolidated marine rocks of the Tertiary-age Great Valley sequence, which in turn are underlain by a basement complex of metamorphic and igneous rocks of pre-Tertiary age. 3.2 Regional Hydrogeology and Water Usa e The Great Valley geomorphic province is divided into three hydrologic basins: the Sacramento River Basin, the San Joaquin River Basin, and the Tulare Lake Basin. The city of Tracy is located within the San Joaquin Delta Hydrographic Unit of the San Joaquin River Basin (RWQCB, 1994). The general movement of groundwater within the Central Valley is from the flanks of the Sierra Nevada Mountains toward the axis of the Great Valley structural trough, which is located on the western side of the Central Valley, nearer to the Coast Ranges. The regional direction of groundwater flow then runs parallel to the axis of the trough, approximately north-northwest, towards the inland delta. The groundwater flow system in the Central Valley has been greatly altered by large-scale groundwater development and very large 3001-21.cap 5 HORIZON ENVIRONMENTAL INC.