The Fifield-Cahill Ridge Trail is currently the only segment of the Bay Area Ridge Trail that has restricted access, requiring visits to be docent-led. The standard “through hike” goes southbound from a trailhead on Sneath Lane in San Bruno via the Portola Gate, at the southern end of Sweeney Ridge, to a trailhead at Quarry Road near CA-92. The link to the Fifield-Cahill Ridge Trail web site goes to a page where you can sign up for a hike, mountain bike ride, or equestrian ride. Between Portola Gate and Quarry Road the trail passes through property managed by the San Francisco PUC as watershed land.
The hike actually has three sections: From Sneath Lane to Portola Gate the Bay Area Ridge Trail is open without the docent restriction. The northern portion of the Fifield-Cahill Ridge Trail follows Fifield Ridge Road to Five Points and is more out in the open, with scrub vegetation. The portion south of Five Points follows Cahill Ridge Road and is more in the forest. At various points there are spectacular views of San Francisco Bay, the Pacific Ocean, and several of the reservoirs for which the watershed area was created.
The starting elevation is about 200 feet higher than the ending elevation, so there is a bit more downhill than uphill when hiked in the southbound direction.
The trail from Sneath Lane to the Ridge Trail on Sweeney Ridge is paved and climbs 600 feet in 1.7 miles. Along the way there are views of San Andreas Lake, the northernmost PUC reservoir in the watershed. It is noteworthy that the infrastructure and dams that create the reservoirs were built prior to 1890, so prior to the 1906 earthquake. On the day of this hike the morning marine layer had not yet burned off, though it did so later on.
Right at the Tee junction with the Bay Area Ridge Trail there is a wonderful vista point from Sweeney Ridge out over the Pacific Ocean. The Sweeney Ridge portion of the trail is in Golden Gate National Recreation Area. Although the famous coastal fog was off-shore, we were unable to see the Farallon Islands. It was still beautiful!
Near this junction is the San Francisco Bay Discovery Site, where Spanish explorer Gaspar de Portola was the first European to see San Francisco Bay. The Discovery Site is a great place to visit in clear weather, as it is possible to see landmarks from Point Reyes to Loma Prieta. The trail itself is a wide service road. The open terrain provided continuous viewing of this ridgeline we seemed to be heading toward, to the southeast.
As we passed through Portola Gate into the watershed land, we looked behind us to see South San Francisco against the San Bruno Mountain ridge, a reminder that we were simultaneously close to, and remote from, the city. The Ridge Trail mileage in the stats box for this hike begins at Portola Gate.
I happened to notice this beautiful early-season wild iris next to the trail.
Once you are within the watershed and on Fifield Ridge Road, the trail turns southwest and descends about 200 feet before turning again to the southeast and regaining the elevation, plus another 200 feet. About 1.9 miles past Portola Gate there is a spot with a great view of Mt Tamalpais.
From the same spot there is another great view of the Pacific Ocean and CA-1, generally in the area of Devil’s Slide south of Pacifica.
After the high point at 1400 feet elevation, the trail loses 600 feet in 2 miles. Along the way, there is a section overlooking San Francisco Airport and San Francisco Bay, with Mt Diablo in the background. It was tempting to just stop for awhile and watch planes land at, and take off from, SFO.
There was now another beautiful ridge, I believe Spring Valley Ridge, between Fifield Ridge and the ocean.
About 4.3 miles south of Portola Gate is Five Points, where five trails come together. At Five Points the Bay Area Ridge Trail leaves Fifield Ridge Road and continues on Cahill Ridge Road. The terrain changes from open scrub-covered hills to forest. Here is a fine example of a multi-trunked tree; many trees with this shape are bay trees.
About 3.8 miles past Five Points is Cemetery Gate, where some hikes access the trail. Perhaps 0.2 mile farther, the trail begins a steady 600-foot descent toward the Quarry Road trailhead. Near the beginning of this descent there is a relatively open section with views of San Francisco Bay, with Mt Diablo in the background and Crystal Springs Reservoir and I-280 in the foreground.
About 0.5 mile before the end of the hike, in a small sunny spot in the forest, we saw a pair of perfect spider webs glistening in the afternoon sunlight.
This docent-led group hike was very enjoyable. The small effort required to sign up in advance is more than worthwhile. The docents are knowledgeable about the watershed and its history. Each group visit seems to be monitored by a watershed staff member, and we encountered ours several times as we leapfrogged each other down the trail. He had even more information about the watershed and local natural history, which added to the overall experience.