Amphibians and reptiles were observed in the Sierra La Madera (59 species), an isolated Sky Island mountain range, and the Sierra Bacadéhuachi (30 species), the westernmost mountain range in the Sierra Madre Occidental (SMO) range in east-central Sonora. These preliminary herpetofaunas were compared with the herpetofauna of the Yécora area in eastern Sonora in the main SMO, where 92 species are known from the Río Yaqui to the Chihuahua border. The Yécora area, as we have defined it, extends from the Río Yaqui to the Chihuahua border along Mexico Federal Highway 16 and other areas accessible from it. Seven species in the Sierra la Madera are exclusive of the SMO fauna. Sky Island faunas are dominated by Madrean species, but also include species with tropical, desert, and northern temperate biotic affinities. Although the herpetofaunas of many Sky Island ranges in Sonora are not well documented, it is clear that the SMO fauna is much more diverse than any of them.