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f <br /> consolidated Tertiary deposits of the Mehrten and Valley Springs <br /> formations and undifferentiated older marine sediments. Beneath <br /> these sedimentary formations lies a basement complex of pre- <br /> Cretaceous metamorphic and igneous rocks (Figure 2 ) . The Victor <br /> and Laguna formations contain the principal fresh-water aquifers <br /> in this region. <br /> The alluvium and the Victor Formation together are roughly 150 <br /> feet thick, and the Laguna Formation is about 1 ,000 feet thick in <br /> the Stockton area. These materials were deposited in flood <br /> plains and alluvial fans. Locally, these units make up the <br /> fresh-water-bearing series, with a total thickness of some 1 , 200 <br /> feet. Lithologically the materials are very heterogeneous. They <br /> are made up of discontinuous sand and gravel beds and lenses, <br /> separated by sandy silt, silty, and clay. On the east side of <br /> Stockton, sand and gravel constitute some 32 percent of the total <br /> fresh-crater-bearing series (DWR 1955 ) . <br /> The Victor Formation and the alluvium have moderate permeabi- <br /> lities and contain unconfined ground water, the Laguna Formation <br /> has moderate permeabilities and contains partially confinecl <br /> aquifers, although there is no evidence for continuous-pressure <br /> aquifers. Recharge to these aquifers occurs primarily by perco- <br /> lation into outcrops in the foothills of the Sierra Nevada, but <br /> local inflitration of rainfall and irrigation water may make a <br /> small contribution. At depths below about 1 ,000 feet, in the <br /> pre-Pliocene formations, saline water is encountered. Fresh and <br /> saline waters are separated by lenses of clays and agglomerates <br /> (DWR 1955, 1967 ) . <br /> The regional water table was nearly horizontal in fall 1985, at a <br /> depth of about 50 feet (FCWCD 1985 ) . In spring 1186, the water <br /> table, again at 50 feet, had a gradient of about J.0007 , down to <br /> the north-northeast (FCWCD 1986 ) . Under such circumstances, the <br /> local direction of ground-water flow can be expected to be <br /> affected by the pumping of water supply wells in the vicinity. <br /> c23/72g2 2 <br />