Maurice Thorner Memorial Open Space Preserve,
Marin County Open Space Preserve,
Marin County

In brief:
1.9 mile out and back hike in a small preserve with grassland and rolling hills.

Distance, category, and difficulty:
This nearly 2 mile out and back hike is easy. The preserve's lowest elevation is about 300 feet. Highest elevation is about 520 feet. Hiking is easy in this small preserve.

More sun than shade.

Trail traffic

Trail surfaces
Dirt trails.

Hiking time
1 hour.

Nice any time.

Getting there:
From US 101 in Marin County, exit San Anselmo/Sir Francis Drake. Drive about 11 miles west on Sir Francis Drake, and turn right onto Nicasio Valley Road. Drive about 0.4 mile, then park on the side of the road near the open space gate.

Get driving or public transit directions from Transit and Trails:

GPS coordinates* for trailhead:
Latitude 38 1'14.22"N
(* based on Google Earth data, shown as degrees, minutes, seconds)

Gas, food, and lodging:
Gas, pay phone, stores and restaurants back east in Fairfax. For breakfast before, or lunch after a hike, I recommend Two Bird Cafe on San Geronimo Valley Drive in San Geronimo (visible from Sir Francis Drake). No camping.

Trailhead details:
No parking or entrance fees. Substantial roadside parking. No maps, drinking water, or designated handicapped parking. Pit toilets inside Roy's Redwoods Preserve. There is no direct public transportation to the preserve, but Golden Gate Transit bus #23 services San Geronimo Valley Drive. From there you could walk about 0.5 mile to the trailhead

The preserve's single trail is closed to cyclists. Dogs are permitted.

The Official Story:
MCOSD's Maurice Thorner page.
Marin County Department of Parks, Open Space, and Cultural Services: (415) 499-6387

Map Choices:
• Use AAA's San Francisco Bay Region map to get there
• Download the pdf map from MCOSD
• Don and Kay Martin's Hiking Marin has a useful map of the preserve and the surrounding area (order this book from
• Barry Spitz's Open Spaces (order this book from

Maurice Thorner Open Space Preserve in a nutshell -- a printable, text-only guide to the featured hike.

View photos from this hike.

Go to Bay Area Hiker Home page


Maurice Thorner Memorial is a tiny and little-known open space preserve near San Geronimo in Marin County. Trailhead photoFor years, the only access was at the end of Lagunitas School Road, and the single trail ended at a hilltop overlooking a golf course and Roy's Redwoods. In September 2000, MCOSD completed an extension connecting Maurice Thorner Memorial with Roy's Redwoods (via the golf course bridge). This permits hikers to explore the two small preserves in once visit.
     Summer and autumn are best spent elsewhere. There is little shade on the ridge, and Thorner Memorial lacks significant foliage trees. The grassland retains some late spring wildflowers, and you might enjoy the preserve in late winter, when the ridge is swathed in fresh green grass.Roy's Redwoods
     Although Thorner Memorial has its own trailhead at the end of Lagunitas School Road, parking is limited there and restricted during school hours. Roy's Redwoods Open Space Preserve provides easier access, and since Thorner is small, you probably won't mind adding a little extra mileage to your hike. Start at the open space gate on Nicasio Valley Road. Turn right (looks like the path ends at the portable toilets, but it doesn't), and follow the signposts for horse traffic. The narrow path, open to hikers and equestrians only, goes right at the toilets, then becomes indistinct in a pretty redwood grove. Stay to the right of the creekbed (although there's another trail on the other side), and look for a path heading south out of the woods. Blackberry brambles crowd the trail. Thorner RIdge TrailThe trail crosses a bridge; turn right on the far side. Ascending easily, Loop Trail soon leaves the woods behind and enters grassland. Nicasio Valley Road is visible as the trail parallels the road. After a few gentle dips, the trail reaches an unsigned junction at 0.26 mile. Bear right and cross the golf course bridge. At the end of the bridge, Thorner Ridge Trail begins at an unsigned junction. Turn left.
     Thorner Ridge Trail, open to hikers and equestrians, ascends gently. Coyote brush is common, as are invasive broom plants. You might see Ithuriel's spear, yellow mariposa lily, and clarkia in late spring. Spiky teasel plants line the narrow path. There are nice views past the golf course back to Roy's Redwoods. Thorner Ridge Trail crosses through a patch of stunted blackberry and soon after reaches the ridge line, joining the preserve's previously existing trail. Bear right.Thorner Ridge Trail
     Pure grassland is interrupted by occasional coyote brush shrubs as the trail runs along the ridge at an easy grade. The lookout at Samuel P. Taylor is visible to the west, as is the ridgeline in Giacomini Open Space Preserve, to the south. A look back to the east reveals White's Hill and Loma Alta. Thorner Ridge Trail approaches and then enters a compact forest of madrone, coast live oak, big-leaf maple, California bay, nutmeg, and hazelnut. Beware of poison oak. Switchbacks wind downhill, and as the trail reemerges into grassland, the end of the preserve is in sight (you may want to turn around here). The trail descends on broad switchbacks, and ends, at 0.97 mile, near a school. Retrace your steps back to the trailhead.

Total distance: 1.94 miles
Last hiked: Wednesday, June 6, 2001