Mussel Rock is a rock formation on the coast of San Mateo County, California, offshore from the city of Daly City. It consists of one large and numerous smaller rocks of a type known as a stack, where a headland is eroded unevenly, leaving small islands.
It is best known for being the closest point to the epicenter of the 1906 San Francisco Earthquake, and where the San Andreas Fault enters the San Francisco Peninsula from the northwest. An additional minor fault, the Mussel Rock Fault, was identified in 2000.
The area above Mussel Rock consists of steep cliffs with frequent landslides, threatening homes in a subdivision above. The adjacent area is a city park.