Surficial geology and geologic hazards of the Tucson Moutains, Pima County, Arizona: Avra, Brown Mountain, Cat Mountain and Jaynes Quadrangles

This report and accompanying maps describe the surficial geology, geomorphology, and geologic hazards around the Tucson Mountains, on the western margin of the Tucson metropolitan area. The mapping covers the Avra, Brown Mountain, Cat Mountain, and Jaynes 7 1/2’ quadrangles and includes part of the City of Tucson and unincorporated Pima County (Figure 1). The map area encompasses the western edge of the Tucson basin floor, the eastern half of Avra Valley, and the Tucson Mountain foothills on the eastern and northern flanks of the Tucson Mountains. The Tucson basin floor area has been thoroughly altered by urban development, and the Tucson Mountain foothills have undergone substantial development during the past 30 years or so. The steeper mountain slopes generally are within Tucson Mountain Park (Pima County) or the western unit of Saguaro National Park, but development is occurring immediately adjacent to these parks. This report is intended to enhance our understanding of the surficial geology around the Tucson Mountains and to aid in assessing and understanding geologic hazards in this area. This new mapping complements previously published bedrock mapping (Lipman, 1993). This surficial geologic mapping in the western portion of the Tucson area is part of continuing efforts by the AZGS to map the geology of the Phoenix – Tucson urban corridor. It builds on and complements previous surficial geologic mapping efforts in the Tucson area (McKittrick, 1988; Jackson, 1989; Demsey and others, 1993; Field and Pearthree, 1993). The report is organized into a brief introduction and explanation of mapping methods, unit descriptions, a summary of the geologic and geomorphic framework of the area, and a discussion of geologic hazards. Tim Orr digitized the map information, generated the final linework and map layout, and provided quality control for the map compilation. Pete Corrao assisted with map and report layout. Mapping was conducted as part of the STATEMAP Program of the U.S. Geological Survey, contract #98HQAG2064. (21 pages and two map sheets, map scale 1:24,000)