Gary Giacomini Open Space Preserve,
Marin County Open Space District,
Marin County
In brief:
4.1 mile out and back hike over a lonely rocky ridge above Woodacre.

Distance, category, and difficulty
This 4.1 mile out and back hike is moderately easy, with a total elevation change of about 700 feet. Trailhead elevation is about 800 feet. The preserve's highest elevation is 1418 feet. The trail along the ridge has some steep and rocky hills.

Mixed sun and shade.

Trail traffic
Light .

Trail surfaces
Dirt trails and fire roads.

Hiking time
2 hours.

Very pretty in early spring.

Gas, food, and lodging:
Pay phones, gas, stores, and restaurants in Fairfax. No camping.

Getting there:
From US 101 in Marin County exit Sir Francis Drake/San Anselmo. Drive west on Sir Francis Drake about 9.5 miles, then turn left onto Railroad Avenue (near Woodacre). Drive about 0.5 mile, then turn right onto Carson Road. Drive uphill on narrow and winding Carson Road for about 1 mile, where the road ends at Conifer Way. Make a very sharp left turn onto Conifer Way and drive slowly up this dirt road about 0.2 mile, to the open space gate at the end of the road.

Get driving or public transit directions from Transit and Trails:

GPS coordinates* for trailhead:
Latitude 38 0'18.21"N
(* based on Google Earth data, shown as degrees, minutes, seconds)

Trailhead details:
Parking for 3 vehicles in a rough dirt area near the gate. If those spaces are full, drive back down to Carson Road and park on the side of the road anywhere legal. Local restrictions demand that cars park at least 6 feet from the center of the road, so look for a pullout all the way off the pavement. This is absolutely a bare bones trailhead. No maps, no toilets, and no parking or entrance fees. No designated handicapped parking, and there is no wheelchair access. There is no direct public transportation to the trailhead, but Golden Gate Transit's #23 bus runs along San Geronimo Valley Drive, and you can walk into the preserve on Bates Canyon Trail, which departs from San Geronimo Valley Drive.

All trails are multi-use. Dogs are permitted on leash on trails; off leash under voice command on fire roads. Dog owners must have a leash for each dog.

The Official Story:
MCOSD's Giacomini page.
MCOSD field office 415-499-6405

Map Choices:
pdf map from the MCOSD website.
Open Spaces, by Barry Spitz, has the best map and detailed trail descriptions (order this book from
Hiking Marin, by Don and Kay Martin, has a useful map and some preserve descriptions, as well as driving directions to other trailheads at this preserve (order this book from
The Bay Area Ridge Trail, by Jean Rusmore (order this book from, has a decent map and descriptions of the Ridge Trail segment though the preserve.

View 50 photos from the featured hike.

Go to Bay Area Hiker Home page

For those who love hiking on Tam but experience seasonal weariness due to fair weather crowds and that "been there, done that," feeling, have I got a preserve for you. TrailheadGary Giacomini Open Space Preserve, which runs along the north side of the San Geronimo Ridge between Sir Francis Drake and Fairfax-Bolinas Road, will have you looking at northern Marin County in a whole new way, literally. There's excitement and drama (driving on tiny winding roads, searching for the trailheads, gambling on the availability of parking), and a rugged, unsigned trail system not for sissies. Besides the surprisingly remote feeling of Giacomini, the main trail, San Geronimo Ridge Fire Road, affords amazing views of northern and western Marin County, including a clear sight of Sugarloaf Ridge on a fog-free day. When the crowds throng to Tam, and you just can't stand to get stuck behind another slow-moving car full of out-of-towners on the way up to Ridgecrest, it's nice to have a no-frills, no-tourist preserve in your repertoire.Conifer Fire Road
     The preserve's long ridge-top route is a favorite for cyclists combing Giacomini's fire roads with MMWD's Pine Mountain Road. For hikers short loops are pretty much out of the question, although if you treat the side of San Geronimo Valley Road as a trail you can combine that street with Conifer Fire Road (via Bates Canyon Trail), San Geronimo Ridge Fire Road, and Sylvestris Fire Road for a 5 mile trek. Out and back hikes from three trailheads above San Geronimo Valley Road and one near the edge of Samuel P. Taylor State Park involve a climb to the ridge line and then a stroll along San Geronimo Ridge Fire Road. From the trailhead at the end of Conifer Way hikers can ascend to the ridge, then walk east out-and-back to the top of White Hill. Grassy hillside provide contrast to woods and cypressThis is a nice alternate to the featured hike, or a 3 mile add-on, but it's a bit of a roller coaster route.
     Most of the ridge is under full sun and can get super hot. Spring and autumn are good seasons for a visit. In spring there are good flowers on chaparral shrubs and through the grassland. Parts of San Geronimo Ridge Fire Road are steep and rocky, so even short hikes can exhaust your feet and lower legs. Sturdy hiking boots, and plenty of drinking water are a must.
     For the featured hike, start at the open space gate at the end of Conifer Way (or, if you've parked on Carson Road, walk to the end of Conifer Way). Initially, the trail climbs through grassland, but at about 350 feet, you'll take a curve to the right near a water tank and head under the shade of madrone, Douglas fir, and California bay. San Geronimo Fire RoadOn the slope of the hill to the right, some bush poppy and manzanita struggle for sun. In more shaded stretches hazelnut and monkeyflower are common. Forget-me-nots bloom in the spring, along with strawberries and iris, and you may even see a few striking red spotted coralroots, a saprophytic orchid. The grade shifts from moderate to steep, and the shade is delicious on a hot day. Conifer Fire Road emerges into grassland, and continues to climb. Views back to the north are impressive, and they only get better. Spring flowers along the fire road include blue-eyed grass, California poppy, and fiddlenecks. Look for a spot off the right side of the trail between two hills, where in the spring creamcups and California buttercups sprawl through the grass, and checker-blooms provide a burst of pink color. At 0.80 mile, a connector path breaks off on the left. Continue to the right on Conifer Fire Road.
     More spring flowers can be found along the trail here, including scarlet pimpernel and redmaids, but creamcups dominate. View of the forested San Geronimo Ridge At 0.91 mile, Conifer Fire Road ends at an unsigned junction with San Geronimo Fire Road. Turn right onto San Geronimo Ridge Fire Road.
     The land on the left side of the trail is part of the Marin Municipal Water District, while the land to the right is Marin County Open Space District property. The fire road crosses a fence line, and abruptly, it's like stepping into another world. Gone are the treeless grassy slopes, replaced by a rocky, chaparral plant community and many shrubby sargent cypress trees. The fire road climbs easily, through manzanita, chamise, chaparral pea, and toyon. Jackrabbits and lizards are common on the ground, and in the air you may see hawks and vultures. White and purple iris seem out of place, but flourish in spring along with paintbrush, mission bells, and zigadene. Where foliage is low, look to the right of the trail (north), for far-reaching views that include the tallest hills in northern Marin County, such as Big Rock Ridge and Black Mountain, and even stretch to Sugarloaf Ridge in Sonoma County. San Geronimo Fire RoadForested Mount Wittenberg, on the Point Reyes Peninsula, is evident to the west on a clear day. Although the little town of San Geronimo is a short distance downhill, the ridge is very quiet. I wonder how many people, if magically transported to this part of the preserve, could correctly identify their location. I always feel like I'm somewhere more remote than Marin County. After a mostly level stretch, the trail begins a moderate descent. At a flat spot, San Geronimo Ridge Fire Road comes to an unsigned junction at 1.88 miles. Pine Mountain Fire Road drops down south to Fairfax-Bolinas Road on the left. Sylvestris Fire Road departs on the right side of the trail. (To extend this hike another mile, take Sylvestris to Hunt Camp, turn left, then when you reach San Geronimo Ridge Fire Road again, turn left.) Continue straight uphill on San Geronimo Ridge Fire Road.Kent Lake
     You'll pass through a pocket of woods, with Douglas fir, coast live oak, and madrone. Look for woodland star and shooting star in spring. San Geronimo Ridge Fire Road climbs steeply. Once out of the woods buckbrush, blueblossom, and wavyleaf ceanothus, members of buckthorn family, line the sides of the trail, along with manzanitas, chaparral pea, toyon, chinquapin, and yerba-santa. At 2.10 miles, you'll reach a viewpoint. Look downhill for a spectacular view of Kent Lake. To the south, all three peaks of Mount Tamalpais may be visible. This is the turn-around point for this hike. (You can continue further on San Geronimo Ridge Fire Road if you'd like.) Retrace your steps back to the trailhead.

Total distance: 4.10 miles
Last hiked: Thursday, November 21, 2002