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_ <br /> 101 <br /> 01 . <br /> June 1, 1988 AGS Job Ila. 038032-2 <br /> UNOCAL service Station No. 6981, Stockton, California <br /> SITE CONDITIONS <br /> UEOLOGY <br /> The Service station is located in the Great Central Valley <br /> geomorphic province of California. Areas adjacent to the site <br /> are flat with little topographic relief. The area is underlain <br /> f! b thick <br /> Y a se quence of continental and marine sediments ranging <br /> �1 <br /> in age from Recent to pre-Cretaceous (Department of Water <br /> Resources, 1967) , <br /> The Central Valley has been a sedimentary trough since pre- <br /> Cretaceous time. Most of the pre-Cretaceous to mid-Tertiary <br /> sediments in this portion of the valley are of marine origin <br /> while the late Tertiary to Recent sediments consist primarily of <br /> continental deposits. Depositional and erosional sequences were <br /> primarily controlled by fluctuations in sea level. Fresh and <br /> brackish water lakes formed in the valley resulting in deposition <br /> of lacustrine clay over extensive areas. Higher energy <br /> environments, such ►s rivers and streams, resulting in the <br /> V <br /> deposition of channel sand and gravel. <br /> 4 <br />