San Francisco - Sunset District

San Francisco — Sunset District Geological Photo
   

San Francisco is in close proximity to the San Andreas Fault, a geologically active area. The fault zone is located just under four miles to the west under the Pacific Ocean, located to the left of this image. I wanted to find an area in San Francisco that resonated for me both aesthetically and geologically. The Sunset District is located on the west side of San Francisco and slopes slightly downward toward the Pacific Ocean.

On the day I photographed this image, I walked near the beach and drove through the Sunset District, where I discovered an excavation site for laying flexible gas pipe. That site revealed the uppermost of two layers of sand. Not very far beneath these sands is rock that reveals the story of the geologic disruption of the earth’s crust. The darker layers of rock are from a time of collision when one plate was pushed down below the advancing North American plate. This rock, comprised of serpentine, clays and rock fragments, contains the disturbed remains of that collision during the Cretaceous period.

The Sunset District is today located near a different kind of plate contact—one where the Pacific Plate slides northwest against the North American plate. The San Andreas fault is located at the contact between these two plates. The houses on this street are about four miles to the fault, where the earth’s crustal movements are occasionally felt as earthquakes.

 

San Francisco - Sunset District Diagram