Saguaro National Park encompasses the Rincon Mountains, the Tucson Mountains and surrounding foothills. The park offers a cornucopia of geologic features and rocks. Numerous illustrations and easy-to-read text describe faults, alluvial fans, pediment, volcanic dikes, megabreccia, and triangular dome facets. Rocks commonly encountered include welded volcanic tuff, rhyolite, andesite, granite, gneiss, schist, sandstone, shale, and limestone. Using photographs, simplified geologic maps, and cross-sectional views, the author exposes the 25-million year geologic history of the Rincon and Tucson Mountains.