Agate Beach and Duxbury Reef, Agate Beach County Park - Agate Beach Trailhead, San Francisco: Marin Headlands - Mt Tamalpais - Point Reyes, California

Agate Beach and Duxbury Reef - 0.3 miles

Agate Beach County Park - Agate Beach Trailhead

Waves crash on a shale terrace over Agate Beach and Duxbury Reef

Waves crash on a shale terrace over Agate Beach and Duxbury Reef

Round-Trip Length: 0.3 miles
Start-End Elevation: 30' - 0'
Elevation Change: -30' net elevation loss
Skill Level: Easy
Dogs Allowed: Yes
Bikes Allowed: No
Horses Allowed: No
Related Trails:

Agate Beach and Duxbury Reef - 0.3 Miles Round-Trip

Agate Beach County Park and Duxbury Reef Preserve are located in Bolinas, CA. Duxbury Reef is the largest soft shale reef in California, and one of the largest shale reefs in all of North America. The reef is named after the sailing ship Duxbury that wrecked here in 1849.

Duxbury Reef is part of the Gulf of the Farallones National Marine Sanctuary, encompassing over 1,280 square miles of ocean and shoreline along the northern California coast.

The sanctuary protects 33 marine mammal species, including 20% of California's breeding harbor seal population. Agate Beach covers 6.6 acres, with nearly two miles of shoreline at low tide.

Together, Agate Beach and Duxbury Reef form one of the most biologically rich coastal areas in the Bay Area. A short trail leads from the parking area to Agate Beach, where you may head north on a thin strand bound by high cliffs, or south into the heart of the reef and intertidal zone.

The intertidal zone is an area exposed to air at low tide and submerged at high tide. In Northern California the intertidal zone is about 9' wide between the highest and lowest tides.

Sub-regions and micro-habitats within support an array of fascinating marine creatures such as anemones, barnacles, sea stars, urchins, crabs, mussels, snails, sea cucumbers, sponges and kelp.

The high intertidal zone is the area closest to the beach. It's covered only once or twice a day during high tides. Here you're likely to find shelled mollusks called ribbed limpets, barnacles, and gastropods such as eroded periwinkle, small-shelled snails, and black turban snails.

The middle intertidal zone is exposed at least once a day. Residents of this zone cover themselves with sand and bits of shells to prevent water loss from exposure to wind and sun.

Sea stars push water through an internal canal system to move water through their tube feet, creating suction that enables them to cling to and move around rocks. Sea lettuce, a green algae identified by its bright green color, is common in this zone.

The low intertidal zone is exposed only during a very low tide. Here sea urchins grip to rocks with tube feet and move by shoving its body forward with its teeth, collecting small plants along its way.

The bat sea star, an unusual variation, has a form of webbing between its arms. Giant green anemones can exceed 15 cm wide. Corraline algae, notable for its hard texture resulting from calcification, is critical to the food chain and oxygenation cycles of the intertidal zone.

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Worth Noting

  • The Farallon Islands are home to the largest colony of seabirds in the lower 48 states, and a critical feeding destination for blue and humpback whales.

  • Animals that survive in this variable habitat of intertidal zones are mostly invertebrates, while most plants in the intertidal zone are algae.

  • Duxbury Reef is named after the sailing ship Duxbury that wrecked here in 1849.

Fishing Information

  • Fishing is permitted with a valid California state fishing license. Strict seasonal and species restrictions apply.

Rules and Regulations

  • Dogs are permitted at Agate Beach State Park but must be leashed at all times.

  • It is illegal to remove or disturb any wildlife from the grounds, beaches, or tidepools of Agate Beach and Duxbury Reef.

Directions to Trailhead

Agate Beach County Park and Duxbury Reef Preserve are located in Bolinas, CA.

From Hwy 101 in Larkspur, take the Sir Francis Drake Blvd exit west to Olema, turn left at Hwy 1/Shoreline Hwy, turn left at Olema Bolinas Rd, turn right at Mesa Rd, turn left at Overlook Rd, and turn right at Elm Rd. A large parking lot is at the end of Elm Rd on the left.

Contact Information

Marin County Department of Parks, Open Space, and Cultural Services

Farallones Marine Sanctuary Association

Trip Reports

There are no trip reports on this trail.


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