Pinnacles - A Unique Californian Granitic and Volcanic Formation

Adventurer
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Based in San Diego, Brian Borg maintains a strong focus on family and parenting in his daily life. With a love of the outdoors, Brian Borg has visited natural areas in San Diego and across the state, including Yosemite National Park and Pinnacles National Monument.

Situated in Central California to the west of the Santa Lucia mountains, Pinnacles forms a distinct geological boundary at an active fault line. West of the fault is a granitic basement rock that formed gradually as huge masses of molten lava gradually rose through the Earth’s crust and cooled and solidified about 80 to 100 million years ago. 

East of the fault is a volcanic formation, with rhyolitic magma extruded and deposited 23 million years ago on top of the original granitic basement. Over the millennia, fracturing, faulting, and wind and water-caused erosion have resulted in vertically sculpted rock layers that form cliffs, spires, and pinnacles that can reach hundreds of feet in elevation.

The unique breccias or layered rocks that form the Pinnacles are also found in one other spot, 195 miles to the southeast. This represents a long-term displacement by the San Andreas Fault, which is bringing the Pinnacles north at a rate of 0.59 inches each year.

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