The Mammoth 7½' Quadrangle includes part of the San Pedro River, flanking valley fill, and bedrock on the west side of the valley that forms the Black Hills and the northernmost tip of the Santa Catalina Mountains (Figure 1). Production of this new geologic map continues the Arizona Geological Survey mapping program of the San Pedro River valley. This mapping was done under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992, and was jointly funded by the Arizona Geological Survey and the U.S. Geological Survey under STATEMAP Program Contract award number 07HQAG0110. Mapping was compiled digitally using ESRI ArcGIS software.