Three species of chub coexist in the Green and Colorado rivers: bonytail chub (Gila elegans), humpback chub (G. cypha), and roundtail chub (G. robusta). This Gila complex in the upper Colorado River basin has often been troublesome to taxonomists. Deacon et al. (1979) listed the bonytail chub as an endangereds peciesin Arizona, California, Colorado, Nevada, Utah, and Wyoming, and the humpback chub in Arizona, Colorado, Utah, and Wyoming. Both are listed as endangered species by the U.S. Department of the Interior (1980). Holden and Stalnaker (1970) found intergrades of the roundtail and bonytail chubs and of bonytail and humpback chubs in the upper Colorado River basin; intergradeso f bonytail and humpbackc hubsw eret he more numerous. [...]