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1 ' San Joaquin County, California 131 ' managing all crop residue and by minimizing tillage. should be considered in plans for enhancement of This map unit is in capability units Ills-4 (MLRA-17), wildlife habitat or land use conversion. irrigated, and Vle-4 (MLRA-17), nonirrigated. It is in This unit is suited to irrigated row and field crops. ' vegetative soil group B. The main limitations are subsidence and the high water table. Because this soil is subject to differential 260—Urban land. This map unit consists of closely subsidence, frequent leveling of the fields is needed to built-up areas in cities. Streets, parking lots, buildings, improve the efficiency of irrigation. Areas adjacent to t and other structures cover more than 85 percent of the levees are subject to lateral seepage in wet years when surface. The landscape has been so altered by urban the water level is high. Careful applications of irrigation works that identification of the soils is not feasible. water are needed to prevent the buildup of a high water ' This map unit is not assigned a capability table. Large ditches and small spud ditches provide classification or a vegetative soil group. subirrigation and improve drainage. Subirrlgation, furrow, border, and sprinkler systems are suitable. 261—Valdez sift loam, organic substratum, Where a subirrigation system is used, the water table is partially drained, 0 to 2 percent slopes. This very raised to a depth of 1 toot at planting time and then is deep. poorly drained, nearly level soil is on flood plains slowly lowered during the growing season until it is at p and deltas. It formed in alluvium derived from mixed depth of about 5 feet at harvest time. Levees should be ' rock sources and in the hydrophytic plant remains of checked periodically, and a proper maintenance reeds and tules. Mottles in the profile indicate a poorly program should be developed. Maintaining crop residue drained soil; however, drainage has been Improved by on or near the surface helps to prevent excessive runoff levees and reclamation projects. Elevation is 15 feet and soil blowing and increases the rate of water intake ' below sea level to 5 feet above. The average annual and the organic matter content. precipitation is about 15 inches, the average annual air This map unit is in capability units Illw-2 (MLRA-16), temperature is about 60 degrees F, and the average irrigated, and IVw-2 (MLRA-16), nonirrigated. It is in frost-free period is about 270 days. vegetative soil group E. Typically, the upper part of the surface layer is light brownish gray, mottled silt loam about 14 inches thick. 262—Vaquero-Carbons complex, 8 to 30 percent The lower part of the surface layer and the upper part slopes. These strongly sloping and moderately steep of the underlying material are light brownish gray, soils are on mountains and on the side slopes of mottled silt loam and silty clay loam about 26 inches uplifted, dissected terraces. The native vegetation is thick. The lower 10 inches of the underlying material is mainly annual grasses and forbs. Elevation is 400 to ' dark gray mucky silt loam. Below this part to a depth of 1,100 feet. The average annual precipitation is 9 to 13 60 inches is black mucky peat. In some areas the inches, the average annual air temperature is about 61 surface layer is silty clay loam or mucky loam. degrees F, and the average frost-free period is about ' Included in this unit are small areas of Itano, Peltier, 270 days. Piper, and Ryde soils in landscape positions similar to This unit is 50 percent Vaquero clay and 35 percent those of the Valdez soil. Also included are small areas Carbona clay. The components of this unit occur as of Kingile, Rindge, and Shinkee soils in the slightly areas so intricately intermingled that It was not practical ' lower landscape positions. Included areas make up to map them separately at the scale used. about 15 percent of the total acreage. Included in this unit are small areas of Calla soils on Permeability is moderately slow in the upper part of terraces and Wisflat soils and exposed bedrock in t the Valdez soil and rapid in the organic substratum. convex positions near the top of the slopes. Also Available water capacity is very high. The effective included are small areas of very deep, medium textured roofing depth of the crops commonly grown in the soils on old alluvial fans; areas of soils dissected by county is limited by an apparent water table that is deep gullies; and severely eroded, shallow, medium ' regulated at a depth of 3 to 4 feet by pumping. Runoff textured soils in landscape positions similar to those of is very slow, and the hazard of water erosion is slight. the Vaquero and Carbone soils. Included areas make The rate of water intake in irrigated areas is 0.7 inch up about 15 percent of the total acreage. ' per hour. The hazard of soil blowing is slight. The soil is The Vaquero soil is moderately deep and well subject to rare flooding, which occurs during years of drained. It formed in material weathered from abnormally high precipitation. sandstone.Typically, the surface layer is grayish brown Most areas are used for irrigated crops. This unit clay about 21 Inches thick. The subsoil is grayish brown may provide wetland functions and values. These clay about 4 inches thick. Light brownish gray and light