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h. im W 0 118 main limitation is low rainfall during the growing season. Because the amount of precipitation is not sufficient for annual cropping, the best suited cropping system is one that includes small grain and summer fallow. Maintaining crop residue on or near the surface helps to prevent excessive runoff and helps to maintain tilth and the organic matter content. If this unit is used for homesite development, the main limitations are depth to the very slowly permeable claypan and hardpan, the high shrink -swell potential, and low strength in the claypan. On sites for septic tank absorption fields, the very slow permeability can be overcome by increasing the size of the absorption field, backfilling the trench with sandy material, and installing long absorption lines. Ripping the hardpan improves permeability and thus also improves the suitability of the soil for septic tank absorption fields. Excavation for buildings is limited by the hardpan. Properly designing foundations and footings and diverting runoff away from buildings help to prevent the structural damage caused by shrinking and swelling. Properly designing buildings and roads can offset the limited ability of the soil to support a load. This map unit is in capability units Ills -3 (MLRA-17), irrigated, and IVs -3 (MLRA-17), nonirrigated. It is in vegetative soil group D. 241—San Joaquin complex, 0 to 1 percent slopes. These nearly level soils are on low terraces. The native vegetation is mainly annual grasses, fortis, and scattered California white oak. Elevation is 20 to 110 feet. The average annual precipitation is about 16 inches, the average annual air temperature is about 61 degrees F, and the average frost -free period is about 275 days. This unit is 45 percent San Joaquin loam and 40 percent San Joaquin loam, thick surface. The components of this unit occur as areas so intricately intermingled that it was not practical to map them separately at the scale used. Included in this unit are small areas of Exeter and Rocklin soils on adjacent terraces. Also included, in landscape positions similar to those of the San Joaquin soils, are small areas of moderately coarse textured soils that have a hardpan at a depth of 10 to 20 inches and moderately coarse textured soils that have been ripped and have remnants of claypan and hardpan material. Included areas make up about 15 percent of the total acreage. The San Joaquin soil that does not have a thick surface layer is moderately deep to a hardpan and is moderately well drained. It formed in alluvium derived from granitic rock sources. Typically, the surface layer and the upper part of the subsoil are brown loam about Soil Survey 16 inches thick. The next 10 inches of the subsoil is a claypan of brown clay. The lower part to a depth of 60 inches is a brown and light brown, indurated hardpan. In some areas the surface layer is fine sandy loam or sandy loam. Permeability is very slow in the San Joaquin soil that does not have a thick surface layer. Available water capacity is low. The shrink -swell potential is high. The effective rooting depth is limited by the hardpan at a depth of 20 to 40 inches. Roots are restricted to cracks and the faces of peds in the claypan, which is at a depth of 10 to 20 inches. Water is briefly perched abov the claypan and hardpan after periods of heavy rainfall or irrigation. Runoff is very slow, and the hazard of water erosion is slight. The rate of water intake in irrigated areas is 1.0 inch per hour. The San Joaquin soil that has a thick surface layer i moderately deep to a hardpan and is moderately well drained. it formed in alluvium derived from granitic rocl sources. Typically, the surface layer is pinkish gray loam about 12 inches thick. The upper 14 inches of thf subsoil is brown sandy clay loam. The next 9 inches is brown clay. The lower part to a depth of 60 inches is a brown and light brown, indurated hardpan. In some areas the surface layer is fine sandy loam or sandy loam. Permeability is very slow in the San Joaquin soil thz has a thick surface layer. Available water capacity is moderate. The shrink -swell potential is high. The effective rooting depth is limited by the hardpan at a depth of 20 to 40 inches. Roots are restricted to crack and the faces of peds in the claypan, which is at a depth of 20 to 30 inches. Water is briefly perched abo the claypan and hardpan after periods of heavy rainfal or irrigation. Runoff is very slow, and the hazard of water erosion is slight. The rate of water intake in irrigated areas is 1.0 inch per hour. Most areas are used as irrigated pasture. A few areas are used for homesite development or for irrigated crops. This unit may provide wetland functior and values. These should be considered in plans for enhancement of wildlife habitat or land use conversioi This unit is suited to irrigated pasture. The main limitation is the low available water capacity in some areas. Because of droughtiness. applications of irrigation water should be light and frequent. The watt can be applied by sprinkler and border methods. Prof stocking rates, pasture rotation. and restricted grazin< during wet periods help to keep the pasture in good condition and protect the soils from compaction. If this unit is used for homesite development, the main limitations are depth to the very slowly permeat claypan and hardpan, the high shrink -swell potential. and low strength in the claypan. On sites for septic t�