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San Andreas Fault Trail Exploration

The San Andreas Fault runs nearly the length of the state. See it up close and personal.

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Rating: 3 out of 5 by EveryTrail members
Difficulty: Moderate
Length: 1.1 miles
Duration: 1-3 hours
Family Friendly

Overview:  Most Bay Area residents have felt the earth move—quite literally. You probably know that the San Andreas Fault runs nearly the length ... more »

Tips:  Los Trancos Open Space Preserve, Midpeninsula Regional Open Space District

7 miles west of Highway 280 and 1 mile east of Skyline... more »

  • No Fee Required
  • Open from dawn until 1/2 hour after sunset
  • No facilities, phone, or potable water nearby
  • Pit toilet in the Monte Bello Open Space Preserve parking lot, across Page Mill Road
  • 60 parking spaces in area, 1 handicapped space
  • Trails not suitable for wheelchairs
  • No dogs, bicycles, fires, smoking, or camping
  • No horses on San Andreas Fault Trail

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Points of Interest

1. Looking at Loma Prieta

Standing on the Pacific Plate, you see Black Mountain (left) Mount Umunhum (center) and Loma Prieta (just right) on the North American plate. Two million years ago, boulders shifted from Loma Prieta to the Pacific plate, and moved northward inch by inch for 23 miles.

2. Sag Ponds

San Andreas Lake is a sag pond-one of the features of fault zones. These shallow depressions are places where the earth pulled apart under pressure. There's another sag pond just north of the parking lot. Many are marshy in winter. In the summer they can be harder to spot. Erosion eventually fills in sag ponds.

This boulder is a type of rock... More

3. Bench Geology

How can you tell if a feature is a bench caused by earthquake activity or a streambed caused by erosion, such as water running downhill? Look at how the feature is situated. This bench runs perpendicular to the contour of the hill, not parallel with it.

Just behind the bench is a pressure ridge. You can make your own pressure ridges: Place your... More

4. Fence Line

In the woods you'll see more evidence of earthquake activity. This is a reproduction of a fence line that moved five to seven feet during the 1906 earthquake. In Point Reyes, the land slipped over twice as far because it was closer to the quake's epicenter.

5. Follow the posts

Posts topped with yellow bands mark the main fault break from the 1906 earthquake. Posts with white bands mark minor fault breaks. The San Andreas Fault isn't one continuous fault but is made up of many segments. The ground can move at any time along any of the segments.

6. Underground Spring

There can be a heavy flow of water across here in the spring. The earthquake activity in the area grinds the soil into very fine particles, called "fault gouge." The dirt dams the flow of underground water, which backs up and turns the area into a marsh.

You'll see evidence of human activity here. These are all second-growth trees. The original ... More

7. Horizontal Oaks

Trees grow upward, unless something happens to knock them over. The lower part of this trunk dates from the late nineteenth century, while the vertical section dates from the early twentieth century. Apparently, the 1906 earthquake knocked the tree over, and the branches then became the new main trunks.

8. Bench

Another bench marked by posts with white bands indicates that this is an area of minor quake activity.