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00 ~ C"J FISH AND vvILDLIFE SERVICE; REPORT Description of Basin and Project Area 1. General. - Rifle Creek, a tributary of the Colorado River is formed by the junction of several small mountain streams which rise on the slopes of the Flat Top,Mountains in the White River National Forest, at elevations of about 10,000' m.s.l., in western Colorado north of the town of Rifle. From this source, the stream flows in a general southerly direction for a distanc e of about Z7 miles to its confluence with the Colorado River near Rifle. Elevation of Rifle Creek at its mouth is about 5,300' m.s.l. 2. Physiography. - From the river sources on th~ White River Plateau, characterized by mesas interspersed with isolated lacolithic mountains covered with a sub-alpine spruce-fir forest type, the streams fall rapidly through narrow V-walled canyons for about 10 miles. Fran this point, the streams flow at a very rapid rate through a rugged, highly erodible terrain for a distance of about 9 miles. This intermediate section is sparsely ti1abered with ponderosa -pine, Douglas fir, and one-seeded juniper with a heavy oat brush, skunk brush, service berry, and mountain mahogany understory. Among the grasses, three awn, cheat grass, needle and thread, and western wheat grasses are dominant. Stream bank cover consists of willow, alder, birch, and narrowleaf cottonwood. Soils in this intermediate section consist of a stony clay loam formed from the weathering of shales which overlay deep sandstone formations. At a point about 8 miles upstream from the mouth of Rifle Creek, the Grand Hogback cut s laterally across the valley. The remaining drainage area of Rifle 'Creek between the Grand Hogback and the Colorado River is characterized by mesas dissected by numerous arroyos resulting from flash floods and the cutting action of primary streams which flow through water gaps in the Grand Hogback. Natural vegetation in tIE area between the Grand Hogback and the Colorado River consists of rabbit brush, salt brush, and sage brush with a preponderantly cheat grass understory. 3. Stream conditions. - Stream characteristics in the upper reaches of the watershed are excellent for fish and wildlife. In these reaches, the streams maintain a relatively large and constant flow of clear, cold water. Pools are abundant, bank cover is good, and riffle areas are adequate in the "park" areas. Downstream from abo ut river mile 12 on the main stream and it s tributaries, flash floods and soil conditions tend to make the streams turbid. This turbid condition, together with irri- gation uses resulting in warmed and silted return flow, lowers stream values appreciably. There is no pollution problem in the watershed.