Pinnacles National Park, California

January 05, 2015


Photographer: Marli Miller; Marli's Web site
Summary Authors: Marli Miller

The rocks at Pinnacles National Park include this distinctive-looking volcanic breccia along with andesite lavas and other types of pyroclastic rocks --all of which together suggest stratovolcano origin some 23.5 million years ago. The vertical joints in the breccia greatly influence the style of weathering and erosion in the park and are ultimately responsible for isolating remnants of un-eroded bedrock as individual pinnacles.

But that's just half the story. Pinnacles lies just west of the San Andreas Fault; 195 mi (315 km) to the south, identical rocks of the Neenach Volcanics lie on the east side of the fault. Together, these two bodies of rock provide one of the great piercing points on the San Andreas fault. When brought back together they make one large, deeply eroded stratovolcano. Photo taken on March 25, 2014.

Photo details: Camera Model: Canon EOS 5D Mark II; Lens: EF16-35mm f/2.8L II USM; Focal Length: 17mm; Aperture: ƒ/9.0; Exposure Time: 0.025 s (1/40); ISO equiv: 200; Software: Adobe Photoshop CS6 (Macintosh).