Skotnicki, S.J., 1994, Compilation geologic map of the central Gila Bend Mountains, Maricopa County, Arizona [Fourth of July Butte, Gillespie, Quail Spring Wash, and Woolsey Peak 7.5 min]: Arizona Geological Survey Open-File Report 94-18, 17 p., 1 sheet, scale 1:50,000.