Sugarloaf Dome was emplaced about 80,000 years ago on the east slopes of San Francisco Mountain. The rhyolitic to dacitic dome was the latest eruptive event in the history of the mountain. Eruptive activity at Sugarloaf was accompanied by a multitude of pyroclastic surges that deposited pumice just east of the dome. That pumice was quarried for years - the white areas - as an abrasive and was used recently to season denim jeans, giving them a worn look. (Image courtesy of Google Earth.)
Photographer: Mike Conway
Photo Date: 2017