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San Joaquin County, California 75 alluvium derived from granitic rock sources. Mottles in irrigated, and IVw-2 (MLRA-16), nonirrigated. It is in the profile indicate a poorly drained soil; however, vegetative soil group H. drainage has been improved by levees and reclamation projects. Elevation is 15 feet below sea level to 5 feet 180— Jacktone clay, 0 to 2 percent slopes. This above. The average annual precipitation is about 14 somewhat poorly drained, nearly level soil is in basins. inches, the average annual air temperature is about 60 It is moderately deep to a hardpan. It formed in alluvium degrees F, and the average frost-free period is about derived from mixed rock sources. Mottles in the profile 270 days. indicate a somewhat poorly drained soil; however, Typically, the surface layer is light brownish gray silty drainage has been improved by levees and reclamation clay loam about 15 inches thick. Below this is a buried projects. A few areas are dissected by intermittent surface layer of grayish brown, mottled silty clay loam sloughs that have been filled as a result of land about 19 inches thick. The underlying material to a leveling. Elevation is 5 to 100 feet. The average annual depth of 60 inches is stratified, grayish brown, mottled precipitation is about 14 inches, the average annual air silty clay loam. In some areas the surface layer is silt temperature is about 60 degrees F, and the average loam or mucky loam. frost-free period is about 270 days. Included in this unit are small areas of Dello, Kingile, Typically, the surface layer is very dark gray and Ryde, and Valdez soils in landscape positions similar to dark gray clay about 22 inches thick. The upper 12 those of the Itano soil. Included areas make up about inches of the subsoil is dark gray clay and light gray 15 percent of the total acreage. clay loam. The next 3 inches is a light gray, strongly Permeability is moderately slow in the Itano soil. cemented to indurated hardpan. The next 9 inches is Available water capacity is very high. The effective yellowish brown loam. The lower part to a depth of 60 rooting depth of the crops commonly grown in the inches is a yellowish brown, weakly cemented hardpan. county is limited by an apparent water table that is In some areas the surface layer is silty clay or silty clay regulated at a depth of 3.0 to 4.5 feet by pumping. loam. Runoff is very slow, and the hazard of water erosion is Included in this unit are small areas of Archerdale slight. The rate of water intake in irrigated areas is 0.3 soils and small areas of Jacktone soils that have inch per hour. The soil is subject to rare flooding, which moderately coarse textured overwash. Both of these occurs during years of abnormally high precipitation. included soils are on the slightly higher parts of the Most areas are used for irrigated crops. This unit landscape. Also included, in landscape positions similar may provide wetland functions and values. These to those of the dominant Jacktone soil, are small areas should be considered in plans for enhancement of of Hollenbeck and Stockton soils and fine textured soils wildlife habitat or land use conversion. that are highly calcareous or saline-sodic. Included This unit is suited to irrigated row and field crops. areas make up about 15 percent of the total acreage. The main limitations are subsidence and the high water Permeability is slow in the Jacktone soil. Available table. Because this soil is subject to differential water capacity is moderate. The shrink-swell potential is subsidence, frequent leveling of the fields is needed to high. The effective rooting depth is limited by the improve the efficiency of irrigation. Areas adjacent to hardpan at a depth of 20 to 40 inches. Depth to the levees are subject to lateral seepage in wet years when water table is more than 5 feet, but water may be briefly the water level is high. Careful applications of irrigation perched above the hardpan after periods of heavy water are needed to prevent the buildup of a high water rainfall or irrigation, Runoff is slow, and the hazard of table. Large ditches and small spud ditches provide water erosion is slight. The rate of water intake in subirrigation and improve drainage. Subirrigation, irrigated areas is 0.1 inch per hour. The soil is subject furrow, border, and sprinkler systems are suitable. to rare flooding, which occurs during years of Where a subirrigation system is used, the water table is abnormally high precipitation. raised to a depth of 1 foot at planting time and then is Most areas are used for irrigated crops, orchards, or slowly lowered during the growing season until it is at a vineyards. A few areas are used as irrigated pasture or depth of about 5 feet at harvest time. Maintaining crop for urban development. This unit may provide wetland residue on or near the surface helps to prevent functions and values. These should be considered in excessive runoff and increases the rate of water intake plans for enhancement of wildlife habitat or land use and the organic matter content. Levees should be conversion. checked periodically, and a proper maintenance This unit is suited to irrigated row, field, orchard, and program should be developed. vineyard crops. The main limitations are the slow This map unit is in capability units Illw-2 (MLRA-16), permeability and depth to the hardpan. Because of the