Earthquake Trail

Behind the Bear Valley Visitor Center a paved loop of a little over half a mile follows the San Andreas Fault through the Olema Valley, its line marked on the ground by blue posts. Everything west of it, Point Reyes included, rides the Pacific Plate; everything east rides the North American. The two grind past each other to the northwest, and on the morning of April 18, 1906, the strain let go.

At the end of the posts stands a fence broken in two. The original fence here was offset about eighteen feet by the earthquake, one of the largest displacements found anywhere along the rupture, and the Park Service rebuilt it to show the break. Surveyors after the quake reported as much as twenty-six feet of slip in the Olema area. The state's 1908 earthquake report also carried a local story of a cow that fell into the opening crack and was swallowed but for her tail; the trail's panels tell it without vouching for it.

The fault explains the road. Bolinas Lagoon, the Olema Valley and Tomales Bay lie in one long trough along the rift, and Highway 1 keeps to it most of the way north through Marin.