Saturday, February 3, 2018

Palomarin Beach Trail: from eucalyptus stands to foreshore cobbles

Foreshore rocks at Palomarin Beach: smooth and mollusk-sculpted cobbles

Palomarin Beach Trail
Palomarin Beach is located at the southern end of Point Reyes National Seashore, California. To get to the beach, hike the 0.6-mile-long Palomarin Beach Trail downhill from its junction with Coast Trail. The junction is found in the shade of eucalyptus trees. See the elongated eucalyptus leaves around the signpost in the picture farther below. Some trees show multi-trunked growth. Once leaving the eucalyptus grove, the trail winds down through coastal scrub and clearings with views of the cliff and ocean scenery. After managing a short, but steep trail section to finally be at beach level, you probably want to switch from hiking into beachcombing and rockstepping mode. At low tide, tidepooling at Abolone Point farther north makes for a great foreshore experience.

A cobble with cavities carved out by mollusks
Along the pebbly beach, one not only finds polished and textured rocks of different size, but also sculpted rocks. Those shale and sandstone rocks have a surface with an often dense coverage of thumb-size drill holes—not made by human sculptors, but by rock-boring pholad clams, which, while holding on with their foot, rhythmically move the toothed edge of their shell back and forth and thus excavate a circular cavity [1]. A boring mollusk finally settles, continues to grow and becomes tied to the cavity. Some of the cavities in the cobble shown above still contain shell parts of once-encased living mollusks.
   
A crab using a turban snail shell for protective armor

While certain mollusks escape predation by boring themselves into a soft rock, a crab such as a hermit crab may occupy an empty gastropod shell for protection. Near Abalone Point I saw a crab with a four-whorl turban-snail house wandering on the ground underneath the surface of the gently forward-swashing and backwashing shoreline water.


Signpost with eucalyptus leaves

Getting there

From Stinson Beach, drive north on Highway 1. At the northern tip of Bolinas Lagoon, turn left onto Olema-Bolina Road and after 1.5 miles turn right onto Mesa Road. Drive to the Point Reyes Bird Observatory bend. Continue on the dirt road section of Mesa Road. Depending on your vehicle clearance and possible wash-outs, you may either want to look out for parking (and walk the dirt road) or continue the last one mile to the end, which is the trailhead for Coast Trail. Start out northbound on Coast Trail and find the signed Palomarin Beach Trail junction after less than a mile.
 
Palomarin Beach
Palomarin Beach: a place for relaxation and exploration

References and more to explore

[1] Jules Evens: In the Splash Zone at Point Reyes. Bay Nature, May 26, 2012 [https://baynature.org/article/in-the-splash-zone-at-point-reyes/]. 
[2] Learn About Crabs & Relatives: http://www.asnailsodyssey.com/LEARNABOUT/CRAB/crabHerm.php.
[3] Point Reyes Mollusks: https://www.nps.gov/pore/learn/nature/mollusks.htm.
[4] Jon Erlandson: 12,000 Years of Hunan Predation on Black Turban Snails (Chlorostoma funebralis) on Alta California's Northern Channel Islands [https://www.academia.edu/16892345/12_000_Years_of_Human_Predation_on_Black_Turban_Snails_Chlorostoma_funebralis_on_Alta_Californias_Northern_Channel_Islands].

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