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San Joaquin County, California 57 been improved by levees and reclamation projects. A table. The rare flooding is a hazard. Properly designing few areas are dissected by intermittent sloughs that foundations and footings and diverting runoff away from have been filled because of land leveling. Elevation is 5 buildings help to prevent the structural damage caused feet below sea level to 10 feet above. The average by shrinking and swelling. The slow permeability and annual precipitation is about 12 inches, the average the high water table increase the possibility that septic annual air temperature is about 60 degrees F, and the tank absorption fields will not function properly. The - average frost-free period is about 270 days. slow permeability can be overcome by increasing the Typically, the upper 8 inches of the surface layer is size of the absorption field. Properly designing buildings gray silty clay loam. The lower 11 inches is dark gray, and roads can offset the limited ability of the soil to _ mottled clay. The underlying material to a depth of 60 support a load. A drainage system is needed if roads or inches is variegated olive gray, gray, and dark gray clay building foundations are constructed. Houses, roads, and clay loam. In some areas the surface layer is silty and streets should be constructed above expected flood clay. levels. Included in this unit are small areas of Columbia, This map unit is in capability units Ilw-2 (MLRA-17), Grangeville, Merritt, and Scribner soils in landscape irrigated, and IVw-2 (MLRA-17), nonirrigated. It is in positions similar to those of the Egbert soil. Also vegetative soil group C. - included are small areas of Stockton and Willows soils on the slightly higher parts of the landscape. Included 154—Egbert silty clay loam, sandy substratum, areas make up about 15 percent of the total acreage. partially drained, 0 to 2 percent slopes. This very Permeability is slow in the Egbert soil. Available deep, poorly drained, nearly level soil is on flood plains water capacity is very high. The shrink-swell potential is adjacent to rivers and sloughs. It formed in alluvium high. The effective rooting depth of the crops commonly derived from mixed rock sources. Mottles in the profile grown in the county is limited by an apparent water indicate a poorly drained soil; however, drainage has -table that has been lowered to a depth of 4 to 6 feet been improved by levees and reclamation projects. through drainage systems that require continual Elevation is 5 feet below sea level to 15 feet above. maintenance. Runoff is slow, and the hazard of water The average annual precipitation is about 12 inches, erosion is slight. The rate of water intake in irrigated the average annual air temperature is about 60 degrees areas is 0.3 inch per hour. The hazard of soil blowing is F, and the average frost-free period is about 270 days. moderate. The soil is subject to rare flooding, which Typically, the upper 14 inches of the surface layer is -occurs during years of abnormally high precipitation. gray silty clay loam. The lower part to a depth of 40 Most areas are used for irrigated crops. A few areas inches is black and dark grayish brown, mottled clay are used for homesite development. This unit may loam. The substratum to a depth of 60 inches is light provide wetland functions and values. These should be gray, stratified fine sand, loamy fine sand, and loamy -considered in plans for enhancement of wildlife habitat coarse sand. In some areas the surface layer is mucky or land use conversion. clay loam. This unit is suited to irrigated row and field crops. Included in this unit are small areas of Dello soils in -The main limitations are the slow permeability and the the slightly lower landscape positions. Also included are high water table. General management considerations small areas of Grangeville, Merritt, and Ryde soils in nclude the hazard of soil blowing. Because of the landscape positions similar to those of the Egbert soil. estricted permeability, water applications should be Included areas make up about 15 percent of the total 17egulated so that the water does not stand on the surface and damage the crops. Areas adjacent to acreage. e ut of avees are subject to lateral seepage in wet years when soil P ndrapid,in the sandy is slow in h ubstpratumrwhicheis abart -•-ie water level is high. Careful applications of irrigation depth of 40 to 60 inches. The available water capacity water are needed to prevent the buildup of a high water is high. The shrink-swell potential also is high. The able. Tile drainage can lower the water table if a effective rooting depth of the crops commonly grown in _uitable outlet is available. Furrow, border, and sprinkler the county is limited by an apparent water table at a irrigation systems are suitable. When the wind velocity depth of 3 to 4 feet. Runoff is slow, and the hazard of high in spring, the hazard of soil blowing can be water erosion is slight. The rate of water intake in :duced by properly managing all crop residue and by irrigated areas is 0.3 inch per hour. The hazard of soil 'Minimizing tillage. blowing is moderate. The soil is subject to rare flooding, If this unit is used for homesite development, the which occurs during years of abnormally high ,ain limitations are the high shrink-swell potential, the precipitation. -•ow permeability, low strength, and the high water Most areas are used for irrigated crops. A few areas