LANDSLIDES AND PEOPLE: AN EXAMPLE FROM COASTAL NORTHERN CALIFORNIA

From the late 1800’s, the Seal Cove area in the unincorporated town of Moss Beach, San Mateo County, California has been a favorite spot for weekend homes, small hotels, and restaurants. Inland, the area was historically devoted to farming and livestock. During prohibition, alcohol-related activities were common on this part of the coast, supplying San Francisco to the north with popular illicit beverages. Beach access was important, particularly to bootleggers, and in some places the bluffs were graded to create roads and paths. These would later become areas of accelerated erosion and slope failure.

Geologically, this area is underlain at depth by the Montara Mountain pluton, which has a varied composition and is pervasively fractured and weathered. The top of this unit is marked by an unconformity, and often by a thin, coarse conglomerate, which is in turn overlain by Cenozoic marine and terrestrial sediments. Erosion along this part of the coast takes several forms, from simple raveling on the cliff to large block landslides.

This area of the coast is still a popular residential and business location. San Mateo County Public Works, Planning, and other agencies work with local residents to keep lines of communication strong. Public input is solicited in several ways: through local and regional meetings, through the County’s web site, and as part of the permit process for new construction or repair of existing structures.

Meetings with community members usually include an instructional component. Residents learn about faults, landslides, and the possible effects of the ways in which they maintain their properties. County officials describe every step of the permitting process, and how decisions are made that will affect local residents. The County and state agencies such as CalTrans and the Coastal Commission work together to help residents and visitors maintain safe and easy access to the constantly changing Seal Cove area.