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ZI INC <br /> • composed of volcanic (rhyolhtic source) sandstones, mudstones and tuffaceous ash beds <br /> (Page, 1986) <br /> The primary source of groundwater in the Lodi area is predominantly from the Late Tertiary <br /> and Quaternary non-marine sediments, which comprise the overlying alluvium, and the <br /> Turlock Lake and Laguna Formations (Brown and Caldwell, 1983, 1985, Woodward Clyde <br /> Consultants, 1988, 1991) Dale and others (1966) indicated that although units of non- <br /> marine sediments could be differentiated and mapped on the surface by using <br /> physiographic and weathering criteria, the subsurface equivalents of these units cannot <br /> be mapped with confidence because there is no significant and distinctive physical <br /> appearance in lithology However, Shlemon (1971) mapped three Pleistocene river <br /> channels of the Mokelumne River within the area immediately east of the site The oldest <br /> channel deposits, which Shlemon relates to the Friant Pumice Member of the Turlock Lake <br /> Formation, is present in the Lodi area at a depth of about 250 feet below ground surface <br /> and is reported to be approximately 600,000 years old (Shlemon, 1971) The second <br /> • channel deposit mapped by Shlemon is present at a depth of about 90 feet below ground <br /> surface in the Lodi area and is reported to be 75,000 to 300,000 years old The third <br /> channel deposit mapped by Shlemon is present at a depth of about 40 feet below ground <br /> surface and is reported to be greater than 27,000 years old These channel deposits all <br /> gently dip to the west and can be correlated with subsurface lacustnne clays found to the <br /> west and southwest of the site <br /> 19150011005 14 <br />