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~~ • Soil Mapping Unit 2: Page 5 • ...... Reddish-brown soils of the dry valley s_ Tliis mapping unit is in Sinbad, Paradox, Lisbon and Big Gypsum Valleys, and Dry Creek Basin. It is not extensive but contains soils used for irrigation and those suitable for potential irrigation. ~; i The landscape consists of long; narrow, gently sloping valleys that are surrounded by steep slopes and .cliff s. Each valley has a main intermit- . tent drainageways with numerous gullied tributarie§. Dry Creek Easin is a wide circular valley surrounded byerolling hills. All drainageways are eroded to depths of 10 to 30 feet and widths of 10 to 50 feet. Cover is dominately sagebrush with rabbitbrusti,.shadscale, greasewood, and grass. t ~ ~ - i ~ .~ This unit is composed of about 75 percent:reddish-bro•.an; calcareous soils with light-colored surface layers that~are low in orcanir_ matter. Surface layers and subsoils are moderately coarse to moderately fine textured. Depths to underlying parent material ranges from 30 to Tore than 60 inclies. 1•fost of these soils are suitable for irrigation. Runoff is medium. [.ater holding capacities are moderate to high. About;20 percent of the unit has grayish-brown, moderately fine and fine textured soils derived from h;ancos Shale. The organic matter content is low and salinity is moderate. The soils are calcareous throughout the profile. Runoff is rapid"and the water erosion hazard 'is high. The remaining 5 percent consists of shallow soils with gypswm shale or sandstone at depths of 20 inches or less. Most of; the gypsum is in the upper reaches of Paradox and Aig Gypsum Valleys. T`,ese soils have little vegetation and are seserely eroded. Runoff is rapid and the erosion hazard is high. i Soil ~S~~o~ Unit 3: Rock outcrop and very shello:v soils of the canyons This rr,apping unit is along the Dolores and San P;iguel Rivers and their tributaries. It is the most extensive unit and constitutes about one- third of the basin. Runoff is very rapid because of the steep slopes and shalle•.a soils with lo•.a•.aater holding capacities. Sediment yield is from less than 0.2 to 1.0 acre-feet per square mile per year. The landscape, is characterized by deep sandstone canyons with steep slopes and long very narrow valleys, and floodplains. Small, gently sloping mesas are above the canyons. Sieeply sloping alluvial fans border some of the canyon walls. A'umerous into rnittent drainageways dissect the steep slopes. '1"he dominant ccvcr is pinyon-juniper.. Oak- brgeh, serviceberry, and grass are more abundant at higher elevations because of increased precipitation. Willo-ds and cottonwood trees occupy siaall tracts along the narrow valleys. shore are a few irrigated hay fields where the valleys are wider. ., i