Geologic Map of the Oro Valley 7.5' Quadrangle and the Pusch Peak area, Northeastern Pima County, Arizona, v. 3.0

The Oro Valley 7.5' Quadrangle covers an area, located approximately 25 km north of downtown Tucson, that extends over much of Oro Valley and includes parts of the adjacent Tortolita Mountains and Santa Catalina Mountains. The area was mapped during November 2001 through April 2002 as part of a multiyear mapping program directed at producing complete geologic map coverage for the Phoenix-Tucson metropolitan corridor. A 1:24,000 scale map is the primary product of this study. Previous geologic maps of the area by Banks (1976) and Dickinson (1994), and maps of adjacent areas by Banks et al. (1977), Skotnicki (2000), and Force (2002) were used to focus mapping on areas of interest, but all of the mapping shown on Plate 1 is new and was produced by the authors. The accompanying text describes rock units and other geologic features. This mapping was done under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992. Mapping was jointly funded by the Arizona Geological Survey and the U.S. Geological Survey under STATEMAP Program Contract #01HQAG0098. The Santa Catalina and Tortolita Mountains are part of the Catalina metamorphic core complex, an area where low- to moderate-angle normal faulting has accommodated uplift and exhumation of rocks that formerly resided in the middle crust, at depths of perhaps 5 to 15 km. The mylonitic fabrics on the south side of Pusch Ridge and locally exposed in the southeastern Tortolita Mountains are the product of deep-seated shearing during this uplift and exhumation process (e.g., Davis, 1980; Davis and Lister, 1988; Spencer and Reynolds, 1989; Dickinson, 1991; Force, 1997). Most of the rocks exposed, however, are not mylonitic and were apparently not deeply enough buried to be at temperatures sufficient for mylonitization (e.g., Banks, 1980). Approximately 5 km of displacement on the steeply west-dipping Pirate normal fault uplifted the steep west side of the Santa Catalina Mountains and down-dropped the bedrock beneath what is now Oro Valley (Budden, 1975; Dickinson, 1994).