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TABLE 2 <br /> Generalized Section of Geologic Units, <br /> South Sacramento County and <br /> North San Joaquin County <br /> Geologic Formation Thickness Physical Water-Bearing <br /> Age (feet) Charactenstics Characteristics <br /> HOLOCENE Alluvium 0-100+ Unconsolidated gravel,sand, Gravels and sands act as <br /> silt and clay deposited along important recharge areas and <br /> stream channels,on terraces yield large amounts of water to <br /> and floodplams,and in basins wells Silts and clays are of low <br /> permeability and yield little water <br /> PLEISTOCENE Turlock Lake 0-100+ Heterogeneous mix of poorly Yields large amounts of water if <br /> Formation sorted clay silt,sand,and old stream channels tapped <br /> ravel <br /> PLEISTOCENE Laguna 125-200 Bedded silts,clays,and sands Sand beds will yield moderate <br /> to PLIOCENE Formation Nonvolcanic amounts of water to wells,clays <br /> field little water <br /> PLIOCENE Mehrten 200-1200 Beds of black volcanic sand, Volcanic sands yield large <br /> Formation brown clay and sand zones of quantities of water to wells <br /> volcanic tuff-breccia(lava) Alt Brown sands yield lesser <br /> of andestic origin amounts,clays yield little water <br /> Tuff-breccias yield no water <br /> MIOCENE Valley Springs 75-125 Beds of light colored sand and Of low overall permeability <br /> Formation ash,beds of greenish brown Yields only small amounts of <br /> silty sand,few beds of gravel water to wells <br /> All of rh olitic origin <br /> Primary Source State of California Department of Water Resources Bulletin 118-3, Evaluation of Ground Water Resources Sacramento County July 1974 <br /> 019150011020 <br />