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CE_ Columbia fine sandy loam, channeled, partially drained, 0 to 5 percent slopes, frequently flooded. This very deep, somewhat poorly drained soil is on nearly level to undulating flood plains. It formed in alluvium from mixed rock sources. Mottles in the profile indicate a somewhat poorly drained soil ; however, drainage has now been improved by reclamation projects. Elevation is 10 to 55 feet. The average annual precipitation is about 12 inches, the average annual air temperature is about 60 degrees F, and the average frost-free period is about 270 days. Typically, the surface layer is pale brown fine sandy loam about 12 inches thick. The underlying material to a depth of 60 inches is stratified light gray, brown, yellowish brown and brownish gray mottled silt loam, fine sandy loam and sand. In some areas the surface layer is loam. Included in this unit are small areas of Dello and Merritt soils on similar positions. Also included are small areas of soils that have coarse textured surfaces or that have buried moderately fine or fine textured substrata below a depth of 30 inches. Included areas make up about 15 percent of the total acreage. Permeability of this Columbia soil is moderately rapid. Available water capacity is moderate. The effective rooting depth of crops commonly grown in the area is limited by an apparent water table at a depth of 3 to 5 feet. Runoff is slow and the hazard of water erosion is moderate. The water intake family for irrigation is 1.5. The hazard of soil blowing is slight. This soil is subject to frequent brief to long periods of flooding in December through April. Channeling and deposition are common along streambanks. Most areas of this unit are used for recreational development and wildlife habitat. A few areas of this unit have been converted to irrigated cropland. Where this unit is used for recreational development, general management considerations include frequent flooding and the hazard of soil blowing. Protection from flooding is needed. Drainage should be provided for paths and trails. Areas used for recreation can be protected from soil blowing and dust by maintaining plant cover. Where this unit is used for irrigated row and field crops, the main limitation is the high water table. General management considerations include frequent flooding. Areas adjacent to levees are subject to lateral seepage in wet years when the water level is high. Irrigation water needs to be applied carefully to prevent the buildup of a high water table. Tile drainage can be used to lower the water table if a suitable outlet is available. Furrow, border, corrugation and sprinkler irrigation systems are suited to this soil. Most climatically adapted crops can be grown if the soil is protected from flooding late in spring and early in summer and if artificial drainage is provided. Maintaining crop residue on or near the surface reduces runoff, reduces soil blowing and helps to maintain the water intake rate and organic matter content. The map unit is in capability units IIIw-2 (MLRA-17), irrigated and IVw-2 (MLRA-IT), nonirrigated. This map unit is vegetative soil group A. SAN JOA()UIN COUNTY SOIL SURVEY PRELIMINARY DRAFT 7/90 SUBJECT TO CHANGE