Colorado River cutthroats are thought to have occupied the basin of upper Muddy Creek, a tributary of the Little Snake River (which ultimately flows into the Colorado River) in southern Carbon County, Wyoming. Historical accounts in letters and diaries refer to them as "mountain trout" or "speckled trout." The fish may have begun to disappear from the upper Muddy Creek in the 1850s as a result of physical changes made to the environment by travelers, the introduction of the brook trout and other non-native species, and possibly the over-trapping of beavers, which affected dams and dependent habitats.