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Range DescriptionThis species is known from central and southeastern Arizona (now rare) and extreme southwestern New Mexico in the United States, south through the highlands of western and southern Mexico to Oaxaca, at elevations of 53 to 2,590 m asl (175 to 8,500 feet) (Roden and Schwalbe 1988, Rossman et al. 1996, Stebbins 2003). The Mexican distribution extends from southwestern New Mexico down the Sierra Madre Occidental and western edge of the Chihuahuan Desert to the southern mountains of the Mexican altiplano around Mexico City. There is an isolated population in Sierra Madre del Sur (Rosen and Schwalbe 1988). In New Mexico, this snake is known from the lower Gila Basin, along Duck and Mule creeks in Grant County and near Virden in Hildago County (Hubbard and Eley 1985 cited by New Mexico Department of Game and Fish 1997); may now be eliminated from Duck Creek (New Mexico Department of Game and Fish 1997). In Arizona, it is known from the Santa Cruz Valley east and generally south of the Gila River; also from Agua Fria River, Oak Creek, Verde River, and several upper Salt/Black River sites (Arizona Game and Fish Department 1998). There is an unsubstantiated report from southwestern Texas (Rosen and Schwalbe 1988). See De Queiroz and Smith (1996) for evidence of former occurrence in southern Nevada and adjacent Arizona.