A 2- to 3-meter thick basalt dike cutting gneissic rock exposed adjacent to the loop road at Saguaro National Park East, in the foothills of the Rincon Mountains, Tucson, Arizona. The Rincon Mtns are part of a metamorphic core complex exhumed during Basin and Range Province extension about 20 to 15 million years ago.
Photographer: Mike Conway
Photo Date: December 2017