Long-time Yavapai College professor Dr. Beth Boyd with her geology class examining pyroclastic deposits of Sugarloaf Dome on the lower east flank of San Francisco Mtn., near Flagstaff, Arizona. Emplacement of Sugarloaf Dome was preceded by hundreds of explosive pyroclastic eruptions with pyroclastic density currents sweeping to the east and north. The resulting pumice deposits are exposed in this quarry.
Sugarloaf Dome was emplaced about 80,000 years ago . The rhyolitic to dacitic dome was the latest eruptive event in the history of San Francisco Mountain.
Photos by Russ Pilcher