Accessible only to small groups through a reservation system, the Fifield-Cahill Ridge Trail is well worth the booking effort. Just west of I-280 and Crystal Springs Reservoir (supplier of water to San Francisco and the Peninsula), this haven for endangered butterflies and birds is part of 23,000+ acres of wild open space just beyond city limits. Join a group on a docent-led 2 to 5-mile hike along a wide fire road through Monterey Cypress and old-growth Douglas fir (there’s also a more challenging 13-mile hike or bike route). This area is home to the rare marbled murrelet sea bird, and the San Bruno Elfin and Mission Blue Butterflies; their endangered status is one of the reasons why public use of the trail is so carefully restricted. The hike has multiple vantage points with panoramic views of Crystal Springs Reservoir. Drink it in.
The Fifield-Cahill Ridge Trail can be traveled only through a docent program with the San Francisco Public Utilities Commission. Make a reservation online or call 650-652-3203. There is no fee to hike the Fifield-Cahill Ridge Trail. No dogs.