Monte Bello Open Space Preserve has one big fault

The weather was perfect today for a ramble through two open space preserves and two continental plates. My College of San Mateo Class met at the main Monte Bello Open Space Preserve parking lot along Page Mill Road.

We started out by inspecting some conglomerate boulders at the trailhead. These rocks were moved northward about 23 miles in more than a million years from the west flanks of Loma Prieta. We then proceeded to a spectacular view southward along the San Andreas Fault to Mount Umunhum and Loma Prieta, which is the highest peak in the Santa Cruz Mountains. From there we turned right and downhill on the Stevens Creek Nature Trail, where we descended into a shady forest of oak, Douglas fir, and Bay. Where the trail crosses Stevens Creek we paused to watch newts swimming in the creek.

We continued on the nature trail to where it ascends into a grassy meadow at its intersection with the Canyon Trail. From there we headed north, crossing the San Andreas Fault, which separates the Pacific Plate from the North America Plate. This trail climbs through a bay and oak forest and crosses back over to the west side of the fault just before we stopped for lunch at a large sag pond. Linear pressure ridges, valleys, springs, and a large sag pond are among the many geological features associated with movement on the San Andreas fault. The sag pond, which is filled with cattails, is a good place to stop for lunch. This is where a curve in the fault created a gap that sank and filled with ground water that flows off the ridge and then hits an impermeable layer of rock at the fault. There were many bright red honeysuckle berries on vines growing in

a bush.

After lunch we continued north, stopping to examine an abandoned orchard of English walnut trees. We then crossed Page Mill Road and entered Los Trancos Open Space Preserve. We then followed the Fault Trail, which has a series of posts that mark where the Earth ruptured during the 1906 earthquake. There is a self guided nature trail with stations explaining features associated with fault movement, especially during the big 1906 quake. We posed for photos at a fence that was offset by that quake. From there we continued on to the Los Trancos parking lot and then crossed Page Mill Road to return to the Monte Bello parking lot.

TO GET THERE... The main parking lot is on the south side of Page Mill Road about 7 miles west from Highway 280 and 1.4 miles east from Skyline Boulevard.