The Madrean Archipelago Biological Assessment (MABA) “bioblitz” expedition to Sierra de la Madera (Oposura) near Moctezuma, Sonora, Mexico from 29 July–7 August 2010 included a land snail inventory. Five people searched for both macro- and microsnails in five sites in foothills thornscrub, oak woodland, and pine-oak forest (1225–2080 m elevation) and found 347 individuals of 18 species or forms. Macrosnails included a Sonorella Pilsbry, 1900 species (N = 5) found at four sites, a succineid species (N = 3) from two sites, and one philomycid slug. Micromollusks (< 6 mm) included representatives of seven families. The vertiginid genus Gastrocopta Wollaston, 1878 included eight species/forms. Vallonia perspectiva Sterki, 1892 was the most abundant species (N = 123). This collection adds four species to the 59 previously reported for the state. Seven forms from this southern “sky island”, including the Gastrocopta ashmuni group (=Immersidens ashmuni Pilsbry and Vanatta, 1900) and Sonorella, are characteristic of the Southwestern Mollusk Province (SWMP). Collecting land snails in Sonora has been sporadic because of the difficult terrain and remote locations. Additional efforts and locations should add many more species and clarify biogeographical affinities of this rugged area.