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Rio Blanco County Area, Colorado • • 21 loam, and Patent and Rhone loamy. Also included are small areas of Rock outcrop and soils that are similar to the Blazon and Rentsac soils but are moderately deep. Included areas make up about 15 percent of the total acreage. The Blazon soil is shallow and well drained. It formed in residuum derived dominantly from shale. Typically, the upper part of the surface layer is brown channery loam about 4 inches thick. The lower part is brown channery clay loam about 7 inches thick. The underlying material is light yellowish brown shaly clay loam about 5 inches thick. Soft shale is at a depth of 16 inches. Depth to soft shale ranges from 10 to 20 inches. Permeability of the Blazon soil is moderately slow. Available water capacity is low. Effective rooting depth is 10 to 20 inches. Runoff is rapid, and the hazard of water erosion is moderate to very high. The Rentsac soil is shallow and well drained. It formed in residuum derived dominantly from sandstone. Typically, the surtace layer is grayish brown channery loam about 5 inches thick. The next layer is brown very channery loam about 4 inches thick. The underlying material is very pale brown extremely flaggy loam about 7 inches thick. Hard sandstone is at a depth of 16 inches. Depth to sandstone ranges from 10 to 20 inches. Permeability of the Rentsac soil is moderately rapid. Available water capacity is low. Effective rooting depth is 10 to 20 inches. Runoff is rapid, and the hazard of water erosion is moderate to very high. Most areas of this unit are used for livestock grazing and wildlife habitat. A few areas are used as woodland. The potential plant community on this unit is mainly pinyon and juniper trees with an understory of Indian ricegrass, beardless wheatgrass, Utah serviceberry, mountainmahogany, big sagebrush, and stemless goldenwheat. Smaller amounts of bitterbrush, needleandthread, western wheatgrass, and bottlebrush squirreltail commonly are also present in the potential plant community. The production of forage is limited by rapid runoff and low precipitation. The potential production of the native understory vegetation in normal years is about 550 pounds of air-dry vegetation per acre. If the range is overgrazed, the proportion of preferred forage plants decreases and the proportion of less preferred forage plants increases. Therefore, livestock grazing should be managed so that the desired balance of preferred species is maintained in the plant community. Management practices suitable for use on this unit are proper range use, deferred grazing, rotation grazing, and brush management. Slope limits access by livestock and results in overgrazing of the less sloping areas. Trails or walkways can be constructed in places to encourage livestock to graze in areas where access is limited. Woodland products such as firewood, tenceposts, and Christmas trees are available on this unit. The major limitations in harvesting the pinyon and juniper trees are steepness of slope and poor accessibility. This map unit is in capability subclass Vlle, nonirrigated. It is in Pinyon-Juniper woodland site. 11-Borolllc Calciorthids-Guben complex, 6 to 50 percent slopes. This map unit is on uplands and the sides of terraces. Areas are long and narrow and are 20 to 160 acres. The native vegetation is mainly low shrubs and grasses. Elevation is 5,600 to 6,900 feet. The average annual precipitation is 15 to 18 inches, the average annual air temperature is 41 to 44 degrees F, and the average frost-free period is 80 to 105 days. This unit is 55 percent Borollic Calciorthids that have slopes of 6 to 50 percent and 35 percent Guben loam that has slopes of 6 to 15 percent. The Borollic Calciorthids are on the sides of terraces, and the Guben soil is on uplands. The components of this unit are so intricately intermingled that it was not practical to map them separately at the scale used. Included in this unit are small areas of Work loam and Zoltay clay loam. Included areas make up about 10 percent of the total acreage. The percentage varies from one area to another. The Borollic Calcicrthids are moderately deep and deep and are well drained. They formed in very calcareous alluvial and glacial outwash derived from mixed sources. The surface layer is gravelly or cobbly loam, clay loam, or sandy loam 2 to 5 inches thick. The underlying material ranges from very gravelly sandy loam or cobbly sandy loam to very gravelly loamy sand or cobbly loamy sand. Calcium carbonate content is more than 15 percent. Depth to soft shale or sandstone ranges from 20 to 60 inches or more. Permeability of the Borollic Calciorthids is moderately rapid to rapid. Available water capacity is low. Effective rooting depth is 20 to 60 inches or more. Runoff is medium to rapid, and the hazard of water erosion is moderate to high. The Guben soil is deep and well drained. It formed in thin eolian deposits over calcareous alluvium and glacial outwash derived from mixed sources. Typically, the surface layer is grayish brown loam 6 inches thick. The next layer is brown loam 5 inches thick. The upper 4 inches of the underlying material is pale brown gravelly loam, the next B inches is white very gravelly loam, and the lower part to a depth of 60 inches or more is mainly stratified very cobbly sandy loam that is more than 15 percent calcium carbonate. In some areas the surface layer is sandy loam that is as much as 20 percent gravel and cobbles. Permeability of the Guben soil is moderate. Available water capacity is low to moderate. Effective rooting depth is 60 inches or more. Runoff is medium, and the hazard of water erosion is slight to high.