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San Mateo, California, United States

Fifield-Cahill Ridge Trail Exploration

Although this trail is not open for walk-in use by the general public, volunteer trail leaders head trips 3x a week.

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Difficulty: Moderate
Length: 10.0 miles / 16.1 km
Duration: Half day
Overview: Local nature lovers can enjoy the rare opportunity to hike, bike, or ride their horses through pristine stands of old growth Douglas Fir, evergreen and fragrant coastal scrub while enjoying ridge-top vistas of our watershed lands, reservoirs, the Pacific Ocean and San Francisco Bay. Although this trail is not open for walk-in use by the general public, trained volunteer trail leaders head excursions three days a week.

This Exploration created in collaboration with the Exploratorium.

Tips: Reservations: Online Request Form Call for more info: (650) 652-3203

*Trailhead Locations*

1. Skyline Quarry – access to this trail head is at Skyline Quarry Gate, which is 0.7 miles west of the intersection of Lower Skyline Boulevard and Highway 92. Look for the sign. Drive westbound on California Highway 92 crossing under Interstate 280. The “T” intersection before you cross the reservoir is Lower Skyline Boulevard. Go straight through it. Remain on Highway 92 crossing over the reservoir. After you have passed the reservoir drive approximately .5 mile. Look for a gate on the north side of Highway 92. Enter through the gate. Drive .5 mile to the parking area.

2. Cemetery Gate – access via Skylawn Cemetery.

3. Portola Gate – access via Army Road from the terminus of Sneath Lane.


Trail excursions on foot, bicycle, or horseback.

*Trail Length*

Trail is 10 miles long and is the SFPUC-managed segment of the Fifield-Cahill Ridge Trail from Highway 92 to Sweeney Ridge.

*Trail Connections*

Fifield-Cahill Ridge connects with the 3.7 miles of the Sweeney Ridge Trail open to the public. Visitors interested in connecting their trek on the Fifield-Cahill Ridge Trai

Points of Interest


Fifield-Cahill Ridge Trailhead

The opening of the Fifield-Cahill Ridge trail on Aug. 21, 2003 was notable enough to garner a commemorative plaque and a press conference with then-mayor Willie Brown. The 10-mile trail runs through the watershed that provides and stores drinking water for the San Francisco Bay area. It's a property full of history, reservoirs, and rare and endangered species. Hiking on the trail is restricted to docent-led ventures three days a week, and advanced registration is required.

The commemorative plaque rests fittingly on a boulder of serpentinite, California's state rock. Serpentinite's defining feature is that it originates as crust found on the ocean floor. It only reaches the exposed surface of the earth in subduction zones--geologic areas that produce the kind of earthquakes that California is famous for.

Monterey Cypress Grove

A mile into the trail is a densely packed stand of Monterey Cypress. You might think cypress from nearby Monterey would be native, but in fact, these trees don't naturally grow this far north. They were planted here in the mid-30s, but why and by whom remains a bit of a mystery. The water agency may have believed the trees would gather fog drip, contributing to the watershed. It turns out that's not the case, but the stand remains.

The four reservoirs supply not only San Francisco, but also other reaches of the Bay Area. Here, also in the cypress grove, we find a pipeline for the Coastside County Water District.

One of many signs along the trail reminding hikers that they are walking near San Francisco's water supply.

Douglas Iris

Having been protected for over 100 years, the area along the Fifield-Cahill trail hosts an abundance of plant varieties, and quite a palette of wildflowers in the spring. Here, a Douglas iris.

White, perfumey blooms fill the branches of this Ceanothus tree. Ceanothus is a member of the lilac family that does well in our Bay Area climate. These trees can also be found is gardens around northern California.

Getting a closer look at the Ceanothus flowers.

Wild strawberries dot the forest floor along the trail.

The cow parsnip isn't a parsnip at all, but a member of the carrot family. These tall, leafy plants sport elaborate displays of tiny, white flowers in the spring.

Lower Crystal Springs Reservoir

A lookout point affords a view of Lower Crystal Springs reservoir. The dam that created the reservoir was built in 1888 of interlocking concrete blocks. It survived the 1906 earthquake relatively unscathed, even though the San Andreas fault lies only a quarter mile to the west.

Panning the view from the overlook, you can see most of the Bay Area on a good day, all the way from Berkeley to San Jose to the Santa Clara valley.

Looking further down the peninsula, you can see the San Andreas rift valley, the area's main geologic feature. It was this valley that was flooded to make the upper and lower Crystal Springs reservoirs.

Cemetery Gate, Accessible Trailhead

At Cemetery Gate, a trailhead marks the start of a one-and-a-quarter mile stretch of trail that's accessible for wheelchairs. You can reach the trailhead via Skylawn Cemetery (hence the name), just north of where Skyline Blvd. meets Highway 92. Like other sections of this trail, the accessible portion is available through advance reservation only.

ADA accessible trails don't need to be paved. This one is a dirt trail that is firmly packed and much wider than the required three feet across. It exists on a stretch of trail that is relatively flat. The trail is used by people of all ages, the mobility impaired, and the vision impaired.

Planted Douglas Fir Grove

The accessible trail passes through two very different groves of Douglas fir. This first grove is a group of trees that was planted in the 1960s. At the time, foresters believed that planting trees was the best approach to conservation. Some forest managers have changed their views, however. This forest, for example, now needs to be actively managed to make sure that it doesn't become too susceptible to fire.

The second grove of Douglas fir is old growth, with trees between 200 and 300 years old. Having never been logged, this could be described as "forest primeval." There are about 1000 acres of old growth fir along the corridor that the Fifield-Cahill ridge trail follows.

There is enough moisture in the forest to allow moss and lichen to grow on the bark of the old Douglas firs. In the crooks of large branches, moss and forest debris collect and make a peaty mass that's almost like soil. Sometimes it can even support growing ferns.

Fungus Rot

Along any forest trail, you're likely to see fungus on a few tree trunks. Some fungi help trees, others can take a toll. This little brown shelf is evidence of heart rot, a disease that affects hardwood trees all over the world. It begins when broken tree bark exposes the wood of a tree to the fungus. This particular fungus is Polyporus schweinitzii, a common fungus in the watershed area.

Inside the tree, the fungus does damage to the wood, rotting it out. Initially, the rot may only occur in a small area inside the tree. But over time it can spread, affecting the structural integrity of the tree--to the point where a strong breeze can blow the tree over.

Up close, you can see a pattern characteristic of the fungus Polyporus schweinitzii. Notice how the wood is beginning to break apart in square chunks. This is why foresters call the rot caused by this fungus "brown cubical rot."

At the base of the fallen tree found along the trail is this pile of debris, chunks of rotted wood with the distinctive cubic shape. The unfortunate tree here is a Douglas fir, but this fungus can affect many kinds of trees, including maples, oaks, spruce and pine.

Skyline Ridge

A rest stop along the way presents us with a vista of the watershed...

...and a few logs to serve as picnic benches. Lunch with a view. And just when you need it, there's a bathroom off to the left.

Pilarcitos Resevoir

The area around Pilarcitos reservoir produces an enormous amount of water, held in by exquisitely engineered dams built during the Civil War era. Here, air masses come off the ocean and over the hills, cool, and dump rain. And more rain. It can rain two or three times more in this little valley than in some of the surrounding areas.

Pilarcitos reservoir was the first reservoir constructed in this area to bring water to San Francisco. It's all downhill from here: the water is delivered to the city via gravity, without using pumps.

The SF Water District's logo is, fittingly, the Pulgas Water Temple. The temple was built in 1934 to commemorate the completion of the Hetch Hetchy water system, which links the reservoirs in the peninsula watershed with a plentiful supply of water from the Sierra Nevada mountains. The inscription on the water temple reads, "I give waters in the wilderness and rivers in the desert, to give drink to my people," a quote from Isaiah that struck a chord with a city ravaged by fires after the 1906 earthquake.

Serpentine Grasslands

This grassland area has soils that are rich in serpentinite (the state rock that you may remember from Waypoint #1). Our state rock lends heavy metals like chromium and nickel to the soil, while offering smaller-than-usual amounts of nutrients like nitrogen and phosphorus. Not the friendliest chemistry for many plants, but the flora in this region have adapted to life on this typically Californian soil.

One flower present in abundance is the orange California poppy. No surprise that California's state flower is specialized to live on soils rich in California's state rock. You can also find the state grass, Purple Needle grass, here. It, too, is adapted to serpentine soils.

Blue-eyed grass (Sisyrinchium montanum) is among the flowers found in this serpentine landscape. Despite its common name, this plant isn't a grass at all, but is more closely related to the lily family.

Sidalcea malviflora, also known as Checkerbloom, These lovely pink blossoms are a common site on these PUC lands.

Purple sanicle (Sanicula bipinnatifida) is a member of the carrot and parsley family. A native plant in the region, it's sometimes called a satellite plant because of the shape of its tiny flowers.

Pacific Stonecrop

The Pacific stonecrop (Sedum divergens) is a pretty little succulent that's native to northern California, as well as the Pacific Northwest. In summer it blooms with bright yellow flowers.

The stonecrop leaves start out green, and those that get more sunlight turn pinkish-red. In this image you can see the creeping rhizomes or stolons (above-ground roots) it sends out to spread.

Pacific stonecrop grows in rocky, coastal scrub areas. Preserving its habitat is important, because the stonecrop is the only host plant for the endangered San Bruno Elfin butterfly (Incisalia mossii bayensis).

Castilleja wighti, the Wight's Indian Paintbrush, appears in shades of red, orange, and pink throughout California. Native Americans used them not only as paintbrushes, but also appreciated their color as a cosmetic; some Indian tribes made a hairwash with these flowers that left their locks lustrous.

Lupine Habitat

Near the end of the trail are rocky hillsides covered with a variety of lupines. Lupines have a distinctive star-shaped pattern to their leaves and upright flower stalks that bloom in the spring.

There are over 80 species of lupine in California, and they live in a variety of habitats. This species, a silver bush lupine (Lupinus albifrons), is famous for attracting butterflies and is one of three lupine species that hosts the endangered Mission Blue butterfly.

The leaves of lupine plants grow in these star-like clusters. Each cluster, which technically makes up the leaf itself, can have anywhere between 5 and 28 "leaflets" depending on the species.

What's behind this pattern of hillside baldness? Could it be an insect or soil chemistry? Actually, it's a human maintenance crew. These exposed patches are firebreaks, areas where dried, flammable material has been cleared to lower the possibility of a fire spreading if one were to occur. This is one of many measures the PUC takes to minimize the chance of fire in the watershed.

San Andreas Lake

From the top of the trail's last hill, you can see San Andreas Lake, so named because it sits right on the San Andreas fault. This view rounds out the tour of San Francisco's water supply, being the fourth reservoir you see from the trail. The earlier reservoirs were (in order): Lower Crystal Springs, Upper Crystal Springs, and Pilarcitos.

This fence marks the northern end of the Fifield-Cahill Ridge trail. You can reach this same spot from the other side, via a trail off of Sneath Lane, but you can't cross onto the Fifield-Cahill trail without a volunteer guide to unlock the gate and lead your way.
Pictures in this guide taken by: craigrosa
Nice! Quest does good work. I just uploaded to the phone; I plan to get a group together soon for a ride thru the watershed and Sweeney Ridge.

by rtbern on Jul 22, 2010
This is a great hike, you should sign up and take it! The process is daunting ... the Water District seems overrun by lawyers for no good reason. You have to sign a FOUR PAGE list of absurd rules before the hike (example: You may not bring a model airplane). And the time I did the hike, our docent-led group was under the obsessively watchful eyes of the park rangers ... every few miles a pickup truck would appear just to check up on us. They need a serious attitude adjustment, as their paranoia drives people away. Maybe that's the goal.

But don't let them win! The hike is very nice, and you should take it ... despite the silly politics of the place.

by sammydee on Jul 12, 2010
OK - with the help of our friends at Everytrail (thanks, Chris!), we've ported over the first of our KQED QUEST Science Hikes to the group. Let us know how it looks, and let us know if you've been here. We'd love to hear about & see things you encountered while you were out there, which we may have missed. The science theme for this hike is "watersheds."

by craigrosa on May 03, 2010

Fifield-Cahill Ridge Trail Exploration Trail Map

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About the Author

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Hi. I'm a Senior Interactive Producer for KQED in San Francisco, CA for KQED Science , which covers science,...

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