AZGS' Brad Johnson joined San Diego State University Geology Alumni in the northern Dome Rock Mountains, Arizona, and the southern Big Maria Mountains, California. The two ranges contain 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. Between there and the other person is the entire Cambrian section consisting of Tapeats, Bright Angel schist, and Muav marble.
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. Photo by George Morgan.
