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