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BILLINGS SILTY CLAY LOAM, 0 to 2 percent slopes, Class Its Land (Bc) This soil, locally called adobe, is one of the most important and extensive in the Grand Valley. It is derived from deep alluvial deposits that came mainly from Mancos shale but in a few places from fine-grained sandstone materials. The deposits ordinarily range from 4 to 40 feet deep but in places exceed 40 feet. The deposits have been built up from thin sedi- ments brought in by the streams that have formed the coalescing alluvial fans or have been dropped by the broad washes that have no drainage channel. The thickest deposit, near Grand Junction, was built up by Indian Wash. Although moderately fine textured, this Billings soil permits successful growth of deep-rooted crops such as alfalfa and tree frtdts. Its per- meability is normally not so favorable as that of the Mesa, Fruita, and Ravola soils. Its tilth and workability are fair, but it puddles so quickly when wet and bakes so hard when dry that good tilth can be maintained only by proper irrigation and special cultural practices. Runoff is slow and internal drainage is very slow. • Like all other soils in the area, this one has a low organic-matter content. Under natural conditions it contains a moderate concentration of salts de- rived from the parent rock (Mancos shale). In places, however, it contains so much salt that good yields cannot be used for crops. Generally, this soil is without visible lime, but it is calcareous. In many places small white flecks or indistinct light-colored streaks or seams indicate that lime, gypsum, or salts are present. Soil limitations are classified as severe for local roads and streets (poor traffic-supporting capacity, moderate to high water tables common), shallow excavations (high water table common), and septic tank filter fields (slow permeability, poor internal drainage, seasonal high water table).