8030 - Laserfiche WebLink

Home Browse Search

Green River Valley near the town of Green River, Utah. The San Rafael River enters the Green about 25 miles (40 km) below the town of Green River. The Green River then proceeds south through Labyrinth and Stillwater Canyons in Canyonlands National Park to join the Colorado River. During its course, the Green River drops from about 14,000 ft (4,300 m} near its source to about 4,000 f t (1,200 m) at its mouth, a 10,000 ft (3,000 m) drop in elevation. Historically, the Colorado River has been characterized by great seasonal fluctuations, high turbidities, highly fluctuating temperatures and high dissolved solids. The fish fauna of the Colorado River evolved in such conditions and are adapted to them. However, changes occuring in the basin have severely altered the aquatic system. These include the construction of reservoirs, flow diversions, consumptive use-and the introduction of exotic (i.e. introduced, non native) species. The geological history of the Upper Colorado River Basin is re- counted from exposed deposits ranging from Precambrian to recent. John Wesley Powell (1961) explored the Green River in 1896, described the geologic origin of the river. The existing system has persisted since the Pliocene epoch and has been isolated with surrounding basins for millions of years (Behnke 1980). This period of isolation has been reflected in the fish fauna and Carlson and Carlson (1982) stated that although Homo sapiens dates back to about 35,000 years, fossils of Gila and Ptychocheilus similar to our existing native fishes (Miller 1958) have been traced to the middle Pliocene, or about 8 million years ago. Climatic conditions in the Upper Colorado River Basin are highly variable. This is reflected in precipitation, which ranges from about 50 inches (1.3 m) in the mountains to less than 6 inches (0.2 m) in the arid valleys. Iorns et al. (1965) provided a contrast between wet, cool, high mountains; drier plateaus and low mountains with widely fluctuating temperatures; and dry interior valleys which are hot in summer and very cold in winter. These conditions result in a mixture of plant communities in the Green subbasin ranging from alpine meadows and subalpine and montane forests; mountain brush, pinyon-juniper. forests; sagebrush, greasewood; and grassland communities. Objectives The objectives of this study were provided in the joint Bureau of Reclamation - Fish and Wildlife Service Memorandum of Understanding (MOU), dated April 16, 1979 (contract no. 9-07-40-L1016). Primary emphasis was directed toward habitat requirements and life history information for endangered fishes; Colorado squawfish (Pt~chocheilus lucius) and humpback chub (Gila cypha). Since then the bonytail chub (Gila ele ans) was listed as endangered (USFWS 1980) and the razorback sucker (Xyrauchen texanus) was proposed for listing, as threatened; they have been included as target species.