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San Joaquin County, California 45 precipitation is about 12 inches, the average annual air building foundations are constructed. Houses, roads, temperature is about 60 degrees F, and the average and streets should be constructed above expected flood ` frost-free period is about 270 days. levels. Typically, the surface layer Is brown fine sandy loam This map unit is in capability units Ilw-3 (MLRA-17), about 20 inches thick. The upper 28 inches of the irrigated, and IVw-3 (MLRA-17), nonirrigated. It is in .- underlying material is grayish brown and light brownish vegetative soil group A. gray, mottled fine sandy loam. The lower part to a depth of 60 inches is dark gray, mottled clay. In some areas 134—Cometa sandy loam, 2 to 5 percent slopes. the surface layer is loam. This moderately well drained, undulating soil is on low, ` Included in this unit are small areas of Dello, dissected terraces. It is moderately deep to dense, Grangeville, and Merritt soils in landscape positions weakly cemented sediments. It formed in old alluvium similar to those of the Columbia soil. Also included are derived from granitic rock sources. The vegetation in small areas of Columbia soils that have coarse textured areas that have not been cultivated is mainly annual layers below the clayey substratum. Included areas grasses and (orbs. Elevation is 100 to 300 feet. The make up about 15 percent of the total acreage. average annual precipitation is about 16 inches, the Permeability is moderately rapid in the upper part of average annual air temperature is about 60 degrees F, the Columbia soil and slow in the clayey substratum. and the average frost-free period is about 260 days. Available water capacity is moderate. The effective Typically, the surface layer is brown sandy loam rooting depth of the crops commonly grown in the about 22 inches thick. The upper part of the subsoil is a county is limited by an apparent water table that has claypan of brown sandy clay about 14 inches thick. The been lowered to a depth of 3 to 5 feet through drainage lower part to a depth of 60 inches is brown, dense, systems that require continual maintenance. The weakly cemented sandy loam and sandy clay loam. In effective rooting depth also is limited by the clayey some areas the surface layer is coarse sandy loam. substratum at a depth of 40 to 60 inches. Runoff is Included In this unit are small areas of Montpellier slow, and the hazard of water erosion is slight. The rate soils in landscape positions similar to those of the of water intake in irrigated areas is 1.5 inches per hour. Cometa soil and Redding soils on the slightly higher The hazard of soil blowing is slight. The soil is subject parts of the landscape. Also included are small areas of to rare flooding, which occurs during years of Rocklin and San Joaquin soils in the slightly lower abnormally high precipitation. landscape positions and Cometa soils that have slopes _ Most areas are used for irrigated crops. A few areas of 0 to 2 percent. Included areas make up about 15 are used for homesite development. This unit may percent of the total acreage. provide wetland functions and values. These should be Permeability is very slow in the Cometa soil. considered in plans for enhancement of wildlife habitat Available water capacity is moderate. The shrink-swell or land use conversion, potential is high. The effective rooting depth is limited This unit is suited to irrigated row and field crops. by the dense, weakly cemented sediments at a depth of The main limitations are the high water table and the 24 to 40 inches. Roots are restricted to cracks and the clayey substratum. Areas adjacent to levees are subject faces of peds in the claypan, which is at a depth of 17 to lateral seepage in wet years when the water level is to 25 inches. Depth to the water table is more than 6 high. Careful applications of irrigation water are needed feet, but water may be briefly perched above the to prevent the buildup of a high water table. Tile claypan or underlying sediments after periods of heavy drainage can lower the water table if a suitable outlet is rainfall or irrigation. Runoff is slow, and the hazard of available. Furrow, border, and sprinkler irrigation water erosion is slight. The rate of water intake in systems are suitable. Maintaining crop residue on or irrigated areas is 1.5 inches per hour. near the surface helps to prevent excessive runoff, Most areas are used for livestock grazing or for reduces the hazard of soil blowing, and helps to dryland grain crops. A few areas are used for irrigated maintain the rate of water intake and the organic matter orchards or vineyards or for homesite development. content. This unit may provide wetland functions and values. It this unit is used for homesite development, the These should be considered in plans for enhancement main limitations are the clayey substratum and the high of wildlife habitat or land use conversion. water table. The rare flooding is a hazard. Septic tank Where this unit is used for livestock grazing, general ., absorption fields do not function properly during rainy management considerations include saturated soil periods because of wetness and slow permeability in conditions in concave areas following rainy periods. The the substratum. A drainage system is needed if roads or characteristic plant community is mainly soft chess,