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• The study area also lies within the historic range of the black-footed <br />ferret (Mustela nigripes), which is federally and state-listed as <br />endangered. Historically, the distribution of ferrets in northwest <br />Colorado included the Yampa, White, Gunnison, and Colorado River valleys <br />(CDOW 1978), and was coextensive with the distribution of the white-tailed <br />prairie dog (Cynomys leucurus), its principal prey (Torres 1973). Although <br />the last "official" sighting of the black-footed ferret was recorded in <br />1910 (Felger 1910), at least three reports of ferrets have been recorded <br />since 1970 in Rio Blanco and Delta counties (ERT 1981). More recently, <br />reports of ferrets have been recorded in Grand County, Utah (Cisco and <br />Cresent Junction) and near Mack, Colorado (Bolwahnn 1983). These sightings <br />increase the potential for ferret occurrence in northwest Colorado. <br />However, since prairie dogs (Cynomys spp.), the principal prey of ferrets, <br />have not been observed in or near the Danforth Hills study area, the <br />occurrence of black-footed ferrets is not likely. <br />Occasional sightings of wolverine (Gulo gulp) have been recorded throughout <br />• montane habitats of Colorado. Although suitable habitat for the wolverine <br />exists, the potential for the occurrence of this uncommon species is very <br />low. <br />Lynx (Felix lynx) have been reported to occur in north-central Colorado <br />(OSM 1982). This species is generally associated with extensive forested <br />habitat, therefore habitat suitability and the potential for lynx <br />occurrence are low within the study area. <br />Five federal or state-listed threatened or endangered fishes are known from <br />northwest Colorado: the Colorado River cutthroat trout (Salmo clarki <br />pleuriticus), Colorado squawfish (Ptychocheilus Lucius), razor-back sucker <br />(X~anchen texanus), humpback chub (Gila cypha), and bony tail chub (Gila <br />elegans). The Colorado River cutthroat trout prefers cold, clear headwater <br />streams with gravel substrates. Three populations are known from streams <br />of the Piceance Basin (Lake, Solider, and Trappers creeks) in northwest <br />Colorado (BLM 1980). The Colorado squawfish, bonytail chub, and razorback <br />• sucker require large river channels with quiet, warm, and muddy backwater <br />areas, while the humpback chub prefers deeper areas of such rivers. These <br />4-25 <br />