Mussel Rock
The San Andreas Fault does not end at the San Francisco Peninsula. It runs northwest under the Pacific, and the last place it touches land is Mussel Rock, a sea stack off Daly City where headland erosion has broken the coastline into a jumble of exposed geology. This is where the fault that destroyed San Francisco in 1906 slips beneath the ocean. On any clear day, paragliders launch from the cliffs above, riding thermal updrafts with views of the fault trace below them. It is a place where recreation and seismology share the same airspace.
Where the Fault Meets the Sea
Mussel Rock consists of one large and several smaller rocks of a type known as a sea stack, formed when uneven erosion isolates portions of a headland from the mainland. The erosion here is accelerated by the San Andreas Fault, which weakens the rock along its trace. The coastline at Mussel Rock is actively retreating, with landslides periodically reshaping the cliffs. Homes in the Westlake district of Daly City perch above the unstable bluffs, their backyards ending at drop-offs that grow closer with every winter storm. The geology is dramatic and dangerous in equal measure.
A Paraglider's Launch
The steady onshore winds and the cliff topography at Mussel Rock create reliable updrafts that make this one of the most popular paragliding sites in the San Francisco Bay Area. Pilots launch from the bluffs and soar along the coastline, hovering above the fault trace and the crashing surf. On busy weekends, a dozen colorful wings may be aloft simultaneously. The Mussel Rock Park, managed by Daly City, provides trail access to the bluffs and beach below. The park is also a popular spot for dog walking, hiking, and watching the sunset over the Pacific.
Living on the Edge
The relationship between the Daly City neighborhoods above Mussel Rock and the unstable geology beneath them is one of California's quieter dramas. Homes built in the mid-twentieth century on the Westlake hillside have periodically been threatened by landslides and bluff retreat. The San Andreas Fault does not announce its presence with surface features visible to the casual observer, but the broken, eroding coastline at Mussel Rock makes the geology legible. Standing on the bluffs, looking down at the sea stacks and the churning surf, you are standing on the most famous fault line in the world at the precise point where it leaves the continent.
From the Air
Located at 37.67°N, 122.49°W on the coast south of San Francisco, off Daly City. The eroding coastal bluffs and sea stacks are visible from altitude. Nearest airports: SFO (KSFO, 5 nm southeast), Half Moon Bay (KHAF, 10 nm south). The San Andreas Fault trace is geologically significant in this area.