This ride is very different from any other ride on this website in that the only way of using this trail is by making a reservation for a spot on a guided ride. The ride enters lands in the Peninsula Watershed under the control of the San Francisco Public Utilities Commission, in the hills along the western side of the San Andreas and Crystal Springs reservoirs, which are not open to the public except for guided hikes and guided bike and horse rides. Refer to the "Park Website" link on your left for information and to make a reservation.

Rides are scheduled here fairly regularly. It certainly seems that the rides on their calendar as of this writing are noticeably more frequent than they used to be when I did this ride in the spring of 2009. Though, I seem to remember that they have an off season during the winter. (I could be wrong.) A quick look through their schedule reveals that bike rides are always scheduled on weekends and there's a ride almost every weekend (including a few cases with a ride on both days of the same weekend). Typically, 10 spaces are made available for each ride.

The only thing that can be ridden by these guided rides is Fifield-Cahill Ridge Trail, which is a single trail stretching from Sweeney Ridge to Highway 92 (ignoring, for a moment, a short bifurcation near Highway 92). Note that rides starting from either end are available and different rides are of different lengths, but I don't believe they ever schedule a ride to traverse the entire length of the trail (which is about 10 miles, one way, if I'm not mistaken).

The "guide" for each ride is a volunteer docent, as far as I've seen, and their role doesn't go beyond unlocking the gate, showing the way, deciding where to turn around, taking head counts to make sure that everyone who came in also goes out, and answering any questions that they can for the curious ones in the group. Other than that, it's like any formal group ride where, for better or worse, the pace is set by the slowest riders in the group.

This particular ride starts from the Sneath Lane entrance of Sweeney Ridge. The initial part of Sneath Lane climbs as a paved road closed to motor vehicle traffic. The grade is around 7% and there are nice views of San Andreas Reservoir and down the rest of the Peninsula. After a wide 180-degree curve, a steep segment of the climb begins. For just over a quarter mile, the grade averages something like 13%. Then it eases back again and you shortly find yourself at the ridge top.

Almost immediately after you make it to the ridge top, you'll find a a short connecting trail to a small clearance on the bay side of the trail. This is the Portola Discovery Site; the spot from which participants of the Portola Expedition saw the San Francisco Bay for the very first time. It's essentially the spot at which the existence of the bay was first realized by any European. It's a neat little historic nugget that even many locals may not know about. You'll find an understated monument here memorializing that event.

From here, you take the Sweeney Ridge Trail fire road to the gate where Fifield-Cahill Ridge Trail starts (called "Portola Gate"). Immediately after the gate, the trail makes a sharp turn toward the ocean, and first descends and then climbs steeply. This first mile or so after the gate is the steepest part of the ride, with grades frequently reaching around 15%. The rest of the ride mellows out for the most part, except for a brief steep stretch right before the spot where we turned around to return on this particular ride.

The fire road takes you meandering around completely open hill tops. So, you get to take in wide views of Pacifica and of the Peninsula from vantage points from which you are not accustomed to seeing them. That is pretty much the only attraction of this ride: Getting to see a few parts of the Peninsula that the public normally doesn't get to see.

We reached our turn-around point just when Lake Pilarcitos came into view in the distance, a short distance before the Five Points junction, which is where the trail would have entered any appreciable amount of tree cover. From there, it was a matter of retracing our steps back to Sweeney Ridge.

You'll notice that the route plot also visits the northern end of Sweeney Ridge to see the Nike missile site. (See the photos.) That part of Sweeney Ridge Trail is paved. This ex-military site was one of several around the bay where batteries of guided anti-aircraft missiles were placed during the Cold War years, many of which have now become part of park lands and are reachable on hikes or bike rides. It's not a bad side attraction before you return to your parking spot.