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KLEINFELDER <br /> 2.1.2 Regional Geology <br /> The Great Central Valley of California has been formed by the filling of a <br /> large structural trough or downwarp in the bedrock formations. The trough <br /> is situated between the Sierra Nevada mountains on the east and the Coast <br /> Range mountains in the west. Both of these mountain ranges were formed by <br /> uplifts which occurred primarily during the Jurassic and Cretaceous <br /> periods. The sediments which fill the trough originated as erosional <br /> debris from the adjacent mountains and foothills. The bedrock complex is <br /> composed of metamorphosed marine sediments similar to those found in the <br /> foothills of the western Sierra Nevada and the eastern Coast Range <br /> Mountains. The overlying sediments exhibit a fairly complete <br /> stratigraphic section of Cretaceous, Tertiary, and Quarternary deposits <br /> which have a maximum thickness of approximately 9,000 feet beneath the <br /> Stockton area. <br /> Prior to Tertiary time, sediments were apparently deposited in a marine <br /> environment. Changes in the sea level and subsequent uplifts resulted in <br /> later deposition of sediments in a continental environment. The recent <br /> sediments have been deposited by flooding of the major rivers: San <br /> Joaquin, Calaveras, Mokelumne, and Sacramento. These rivers flow together <br /> in the Sacramento-San Joaquin Delta which presently occupies the area <br /> between Stockton and Antioch. <br /> The near surface unconsolidated sediments are younger in age than the <br /> deeper consolidated rocks and range in grain size from gravels to clay. <br /> 45-88-01 3 <br />