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i ' San Joaquin County, California 119 absorption fields, the very slow permeability can be alluvium derived from granitic rock sources. Typically, overcome by increasing the size of the absorption field, the surface layer and the upper part of the subsoil are backfilling the trench with sandy material, and installing brown loam about 16 inches thick. The next 10 inches long absorption lines. Ripping the hardpan improves of the subsoil is a claypan of brown clay. The lower part F permeability and thus also improves the suitability for to a depth of 60 inches is a brown and light brown, septic tank absorption fields. Excavation for buildings is indurated hardpan. In some areas the surface layer is limited by the hardpan. Properly designing foundations silt loam. F, and footings and diverting runoff away from buildings Permeability is very slow in the San Joaquin soil. help to prevent the structural damage caused by Available water capacity is low. The shrink-swell shrinking and swelling. Properly designing buildings and potential is high. The effective rooting depth is limited roads can offset the limited ability of the soils to support by the hardpan at a depth of 20 to 40 inches. Roots are a load. restricted to cracks and the faces of peds in the This unit is suited to irrigated row, field, and vineyard claypan, which is at a depth of 10 to 20 inches. Water crops. The main limitations are depth to the very slowly is briefly perched above the claypan and hardpan after permeable claypan and hardpan and the low available periods of heavy rainfall. Runoff is slow, and the hazard water capacity in some areas. Because of the restricted of water erosion is slight. The rate of water intake in E permeability, water applications should be regulated so irrigated areas is 1.0 inch per hour, that the water does not stand on the surface and Urban land consists of areas covered by roads, damage the crops. The hardpan limits the suitability for driveways, sidewalks, parking lots, buildings, and other deep-rooted crops. Where feasible, deep ripping of this structures. The soil material under the impervious restrictive layer can help to overcome this limitation. A surface is similar to that of San Joaquin loam. tillage pan forms easily if these soils are tilled when Most areas are used for urban development. A few F wet. Chiseling or subsoiling breaks up the pan. Because areas are used for irrigated crops. This unit may of droughtiness, applications of irrigation water should provide wetland functions and values. These should be be light and frequent. Furrow, border, and sprinkler considered in plans for enhancement of wildlife habitat Firrigation systems are suitable. Returning crop residue or land use conversion. to the soils or regularly adding other organic material Where the San Joaquin soil is used for urban improves fertility, minimizes crusting, and increases the development, the main limitations are depth to the very rate of water intake. slowly permeable claypan and hardpan, the high shrink- This map unit is in capability unit IVs-3 (MLRA-17), swell potential, and low strength in the claypan. On irrigated and nonirrigated. It is in vegetative soil group sites for septic tank absorption fields, the very slow i F D, permeability can be overcome by increasing the size of the absorption field, backfilling the trench with sandy 2242—San Joaquin-Urban land complex, 0 to 2 material, and installing long absorption lines. Ripping percent slopes. This nearly level map unit is on low the hardpan improves permeability and thus also Fterraces. Elevation is 20 to 110 feet. The average improves the suitability of the soil for septic tank annual precipitation is about 16 inches, the average absorption fields. Excavation for buildings is limited by annual air temperature is about 61 degrees F, and the the hardpan: Properly designing foundations and F, average frost-free period is about 275 days. footings and diverting runoff away from buildings help to This unit is 50 percent San Joaquin loam and 35 prevent the structural damage caused by shrinking and percent Urban land. The components of this unit occur swelling. Properly designing buildings and roads can as areas so intricately intermingled that it was not offset the limited ability of the soil to support a load. practical to map them separately at the scale used. The San Joaquin soil is suited to irrigated row, field, F Included in this unit are small areas of Kingdon and and vineyard crops. The main limitations are depth to Tokay soils on the slightly higher parts of the the very slowly permeable claypan and hardpan and the F. landscape. Also included, in landscape positions similar law available water capacity. Because of the restricted to the San Joaquin soil, are small areas of moderately permeability, water applications should be regulated so coarse textured soils that have a hardpan at a depth of that the water does not stand on the surface and 10 to 20 inches and moderately coarse textured soils damage the crops. The hardpan limits the suitability for that have been ripped and have remnants of claypan deep-rooted crops. Where feasible, deep ripping of this F. and hardpan material. Included areas make up about 15 restrictive layer can help to overcome this limitation. A percent of the total acreage. tillage pan forms easily if the soil is tilled when wet. The San Joaquin soil is moderately deep to a Chiseling or subsoiling breaks up the pan. Because the j 1 hardpan and is moderately well drained. it formed in soil is droughty, applications of irrigation water should