Banded gneiss on the Catalina Highway. The coarsely crystalline dark rock is the 1.4-billion-year-old Oracle Granite. The light colored pegmatitic granitic rocks and quartz veins that intrude it are related to the 50-million-year-old Wilderness Suite leucogranites. Online resources: Bezy, J.V., 2016, A Guide to the Geology of the Santa Catalina Mountains, Arizona: The Geology and Life Zones of a Madrean Sky Island. Arizona Geological Survey Down-to-Earth # 22, 83 p. https://library.azgs.arizona.edu/item/DTES-1552428346471-69
Spencer, J.E., 2006, A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona. Arizona Geological Survey Open File Report, OFR-06-01, 38 p https://library.azgs.arizona.edu/item/AOFR-1552429673312-319
Force, Eric, 2001, A Field Trip Guide To Sabino Canyon and the Mount Lemmon Highway, Pima County Arizona: Arizona Geological Survey Contributed Report CR-01-A, 37 p. https://library.azgs.arizona.edu/item/AGCR-1552429793729-601
Photographer: Jon Spencer
Photo Date: circa 2012