Coastal landslides at Mussel Rock Park and Thornton Beach State Park, San Mateo County, California

View looking northward from Mussel Rock Park along the sea cliffs at Thornton Beach State Park (San Mateo County). The rolling slope in the foreground is part of the toe area of a large landslide complex at Mussel Rock Park. The sea cliffs are exposures of the Merced Formation. The Merced Formation consists of poorly consolidated marine and coastal sedimentary deposits that accumulated roughly between 3 and 0.5 million years ago. The Ocean Shore Railroad built along this section of coast in 1905 to 1906 was severely damaged by the 1906 earthquake. Because of ongoing troubles due to landsliding, the rail line was abandoned in 1920. In the 1930s, the rail line was widened to accommodate Highway 1. However, shortly after major landsliding occurred in association with a magnitude 5.3 earthquake on March 22, 1957 the route was once again abandoned. Today only a trace of the highway cut can still be seen about midway up the sea cliff.

The URL of this page is http://3dparks.wr.usgs.gov/landslide/big/23.htm