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J. H. KLEINFELDER & ASSOCIATES <br /> File: W-2001-1 <br /> January 29 , 1986 <br /> Page 16 <br /> During its early depositional history (Pre-Cretaceous to Early <br /> Tertiary) , the Central Valley was open to the sea and sediments <br /> were deposited under marine conditions. In the Late Tertiary <br /> period, the sediments began to be deposited on land and not under <br /> water as a result of a retreating sea and a rising landmass. <br /> Fresh and brackish lakes formed during the latest Tertiary <br /> period. Fine grained material deposited in them to form <br /> extensive clay deposits, most notably the Corcoran Clay Member of <br /> the Tulare Formation. During the Quaternary Period , the <br /> mountains and valley floor were moving, causing accelerated <br /> erosion which contributed to the formation of deltas and alluvial <br /> fans at the apex of the rivers flowing from the Sierra Nevadas <br /> and Coast Ranges. Glaciation in the Sierra Nevadas added to the <br /> process of erosion and deposition as the glaciers advanced and <br /> retreated, releasing or retaining large quantities of water into <br /> the rivers. <br /> Below the site and the Central Valley at great depth, lies the <br /> basement Complex, which is composed of metamorphosed sedimentary, <br /> volcanic , and igneous rocks. Above the basement Complex lie <br /> _ Cretaceous sandstones , siltstones and shales, all of marine <br /> origin . Above the Cretaceous sedimentary rocks lie <br /> undifferentiated Eocene marine sandstone, siltstone, and shale. <br /> Above the Eocene sedimentary marine rocks lie continental to <br />