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- t <br /> July 8, 1988 AGS Job No. 38032-1 <br /> UNOCAL Service Station No. 6981, Stockton, California <br /> GEOLOGY <br /> The site is located in the Central Valla geomorphic Valley g rp province of <br /> California. Areas adjacent to the site are flat with little <br /> topographic relief. The area is underlain by a thick sequence of <br /> ° y continental and marine sediments ranging in age from Recent to <br /> pre-Cretaceous (Department of Water Resources, 1967) . <br /> Most of the pre-Cretaceous to mid-Tertiary sediments in this <br /> portion of the valley are of marine origin, while the late <br /> Tertiary to Recent sediments consist primarily of continental <br /> deposits. Depositional and erosional sequences were primarily . <br /> controlled by fluctuations in sea level. Fresh and brackish <br /> water lakes formed in the valley resulting in deposition of <br /> lacustrine clay over extensive areas,. Higher energy <br /> environments, such as rivers and streams, resulted in the. <br /> deposition of channel sand and gravel: <br /> ex <br /> The site is underlain by very gently dipping Quaternary fluvial <br /> sediments consisting primarily of a clayey silt in the locations <br /> observed to date. The topographic surface in the area is <br /> slightly � <br /> irregular with a general westwardsop <br /> slope.---- — ---- - -- --- -------- - --- - --------- -The-nearest---- <br /> surface stream is the Calaveras River, approximately 0.6-mile <br /> south of- the site. <br /> ks <br /> APpl ed OeoSyStelns <br />