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Ghevron U.S.A. <br /> Page 9 <br /> Soils within the Delta are primarily organic and are generally composed of peats, <br /> organic silts, and clays. The peaks, either fibrous or decomposed to clayey pests, <br /> are found in the centers of the islands at or near the ground surface. The organic <br /> material ranges in uepth from a thin veneer along the eastern edge of the Delta to a <br /> maximum thickness of about 60 feet under a portion of Sherman Island in the western <br /> Dema. The average depth of peat is about 10 feet. With few exceptions,the mineral <br /> soils in the Delta are found along the eastern and southern perimeter, but even here ; <br /> i <br /> the mineral soils are rich in organic matter or contain layers of organic material. <br /> Organic soils are excellent agricultural soils; however, drainage problems and the <br /> high water tal~is reduce their potential pro61ctivity in the Delta. <br /> f <br /> 6.2 Hy_ r 1 i ttin <br /> - The City of Stockton is located in the northern portion of the San Joaquin Basin <br /> ? Hydrologic Study Area, which includes roughly the southern two-thirds of the Great <br /> 'mss <br /> Valley. Within that area,39 groundwater basins and area.,of potential storage have <br /> 3 <br /> been identified. The boundaries of these storage arEas are based largely on <br /> f � <br /> hydrologic as well as political considerations, <br /> The City of Stockton is situated in the western portion of the Eastern San <br /> # Joaquin County Basin proper. Post-Eocene continental rocks and deposits contain most <br /> of the fresh water in the central Valley. These continental rocks and deposits of <br /> Tertiary age include the Mehrten Formation. The Mehrten Formation is of great <br /> importance to the fresh ground-water basins of the Central Valley and yields large <br /> �6ao-a-2o-6-oaa <br /> DAMES Mt ORE <br />