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PRELIMINARY SUBJECT TO CHANGE CB-138 - Columbia fine sandy loam, drained , G to Z percent slopes . This very deep, somewhat poorly drained soil is on nearly level flood plains . It formed in alluvium from mixed rock sources . Mottles in the profile indicate a somewhat poorly drained so i I ; however , drainage has now been improved by levees and reclamation projects . Elevation is sea level to 100 feet. The average annual precipitation is about 14 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 1Z inches thick . The upper- 9 inches of the underlying material is I i ght gray mottled silt loam. The next 5 inches is yellowish brown mottled fine sandy loam. The lower part to a depth of 60 inches is stratified brawn , pale brown and yellowish brown mottled silt loam, fine sandy loam and loamy fine sand . 'In some areas the surface layer is loam. Included in this unit are srna I I areas of De I I o , Egbert , Gr-angev i l l e , Guard and Merritt so i l s on s i rn i t ar- positions and Co3na soils on slightly higher positions . Also included are srna I I areas of Columbia soils with moderately fine textured overwash . Included areas make up about 15 percent of the total acreage. Permeability of this Columbia soil is moderately rapid . Available water- capacity is moderate . Effective rooting depth is 60 inches or more. Improved drainage has lowered the apparent water- table to a depth of 60 inches or more . Runoff is slow and the hazard of water- erosion is slight . The water- intake family for- irrigation i s 1 .5. The hazard of soil blowing is slight . The soil is subject to rare flooding which occurs during years of abnormally high precipitation . Most areas of this unit are used for irrigated cropIand , orchards and vineyards . A few areas are used for homesito development. This unit is suited to irrigated raw, field , orchard and vine crops . It has few limitations. Depth to the water- table is more than 6 feet, but water may be perched above the stratified substratum after- heavy rains or irrigations . Areas adjacent to levees are subject to lateral seepage in wet years when the water- level is high . Furrow, border, corrugation and sprinkler irrigation systems are suited to this soil . Irrigation water- needs to be applied carefully to prevent the buildup of a high water- table . Maintaining crop residue on or near- the surface reduces runoff, reduces