AZGS' Brad Johnson assisted the San Diego State University Geology Alumni group in examining the northern Dome Rock Mountains, Arizona, and the southern Big Maria Mountains, California. Both ranges include Proterozoic basement rocks and highly deformed metamorphic correlatives of Grand Canyon Paleozoic sedimentary rocks. The effects of heterogeneous distributed shear on these rocks is most impressive.
IMAGE. View to the east of part of a north-dipping, overturned, highly attenuated fold limb in the Big Maria Mountains. The person on the left is standing on the unconformity between Proterozoic granitoid rocks (to viewer's left) and the Cambrian Tapeats quartzite. The entire Cambrian section consisting of Tapeats, Bright Angel schist, and Muav marble is confined to the space between the two individuals.
The person on the right is standing on Devonian dolomitic marble. The resistant brown ledge in the lower right corner of the photo, and continuing in the distance behind that person, is the Pennsylvanian-Permian Supai Group. The Mississippian Redwall marble forms a 1-meter-thick white ledge just above the Supai Formation. Photo by George Morgan.
Photographer: George Morgan
Photo Date: March 2018