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S E C O R Conceptual Site Model Chevron Service Station #9-6171 March 25, 2005 Page 2 2.0 SETTING A summary of the regional geology, stratigraphy, and hydrogeology is presented in this section 2.1 Geology IThe San Joaquin Valley comprises the southern two-thirds of the Great Central Valley (Central Valley) geomorphic province (Hackel, 1966) It is separated from Its northern one- third, the Sacramento Valley, by the burled Stockton arch and combined river deltas of the Sacramento and San Joaquin Rivers This 430 mile long structural valley is an asymmetrical synclinal trough with a gently Inclined undeformed eastern limb and a tightly folded and faulted narrow western limb Near Fresno, the valley reaches Its greatest width of 62 miles The Central Valley is bounded on the south by the Tehachapi and San Emigdio Mountains, the east by the Sierra Nevada, the north by the Klamath Mountains, the northeast by the Cascade Range and the west by the Coast Range The basin drains into the San Francisco Bay by the Sacramento and San Joaquin Rivers The structure of the Central Valley is controlled by Its tectonic evolution As subduction of the Kula Plate ended during the Eocene, the formation of the San Andreas Fault became the major tectonic influence Subsequently, numerous folds flanked by normal and reverse Ifaults formed throughout the Central Valley Central Valley depositional settings have ranged from predominantly marine to fluvial in origin The Cretaceous ushered in seas that lasted until the Pleistocene Uplift of the Coast Range from the Pleistocene to present caused the Inland sea to withdraw Following evacuation of the marine environment, freshwater swamps and lakes formed which were eventually replaced by the current system of rivers, deltas, and alluvial fans 2.2 Stratigraphy Ordovician to Jurassic units consist of granite, granodionte, diorite, and metasedimentary shale and sandstone This includes the Sierra Nevada batholith, the Western Metamorphic belt, and the crystalline basement underlying the valley fill The valley fill is a broad clastic wedge that thickens to the west and south Cretaceous and Tertiary strata consist of sediments derived from marine and continental sources in laterally continuous, thick packages of rhythmically interbedded mudstone, slltstone, conglomerate, sandstone, and limestone Quaternary to Recent units are solely continental in origin, consisting of lake deposits and alluvium derived from the Siena Nevada and Coast Ranges Valley fill consists of interfingering detrital material such as non-marine well-sorted sands of the Sierra Nevada and non-marine poorly sorted clays and silts of the Coast Ranges I IN IFileslProlects\Chevron\Retaifl#9-6171\Site Conceptual Model\FINAt__CSM doc