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As shown on Drawing 2, the sediments have been divided into three large groups based on gross lithology and pervasive distinctions in color. Although several strata can be recog- nized in the logs, for purposes of this report they were grouped into the following three larger groups: Group A Surface to approximately 28 to 40 feet—highly interbedded sandy silt, clayey silt, silt, and clay. A few layers of sand are present. Generally sands are fine grained. Most of the sediments have an oxidized appearance, showing an orange brown color. Group B Top-28 to 40 feet deep. Bottom—approximately 55 to 75 feet deep (25 to 35 feet thick)—interbedded sand, silty sand, silt, and clay. Sands are fine grained. Overall, this layer is a little sandier than group A. Sediments are distinctly less oxidized than group A, show- ing a grey brown color. Group C Top-55 to 75 feet deep. Bottom—to lowest available data (approxi- mately 110 feet deep)—Sediments dominated by sand, fine to medium grained; some coarse grained or gravelly layers. A few layers of silt and clay material occur. Color is generally light brown to yellow brown. Grains are large enough to assess and conclude that the sedi- ments appear to be granitic in origin. Surface Soils. The surface soils are mainly composed of two soil types typical of Victor Formation sediments, as shown in Figure 2.5. The two soils, as mapped by the Soil Con- servation Service, are known as Clear Lake clay (CL) and Jacktone clay (ST). These soils are similar in composition; they were formed from alluvium. The most widespread soil type on the site is the Jacktone clay (ST), which covers the nearly flat terrain 100 to 200 feet from the South Fork. Typically, this soil type is found on zero to 2 percent slopes forming a moderately deep hardpan of somewhat poorly drained soil made up of generally dark gray clay about 2 inches thick, underlain by light gray clay loam, followed by hardpan of 3 inches. Permeability is low, the available water-holding capacity is moderate, the shrink-swell potential is high, water may be perched on top of the hardpan following heavy rain, runoff is slow, and the water erosion hazard is slight. The typical uses of this soil type are irrigated cropland, orchards, vineyards, and sometimes irrigated pasture and urban development. The Clear Lake clay (CL) soil type is common along the South Fork. The surface layer is dark gray clay about 29 inches thick followed by another 8 inches of dark gray clay, then S inches of mixed light brownish gray clay loam, then variegated dark grayish brown weakly to strongly cemented hardpan to a depth of 60 inches. The permeability of this soil is low, the available water-holding capacity is moderate, the shrink-swell potential is high, the water erosion hazard is low, and the soil is subject to rare flooding during abnormally a ea10029W.wp5/39 9na/a 39