Rio Grande cutthroat have the distinction of being the southernmost subspecies of cutthroat trout. However, due to the loss of populations across their native range and reports of Rio Grande cutthroat in Mexico and Texas, it is unclear how far south this trout once occurred. The Mexican reports have been all but dismissed, but Garrett and Matlock (1991) provided evidence indicating that Rio Grande cutthroat were likely native to Texas. Today the southernmost known populations are found on the eastern flanks of the Gila Mountains in Southern New Mexico.