Bluff Lookout: Mantle Rocks Exposed

The blue-green serpentinite coastal bluffs.

From here you can see excellent examples of blue-green serpentinite rock. Serpentinite is metamorphosed mantle rock formed in subductions zones when water from the sinking ocean crust alters the surrounding mantle rocks. Because serpentinite is less dense than surrounding rocks, it makes its way to the surface along faults, like a cork rising up to float on water.

Protecting lands, encouraging diversity

Soils above serpentinite rocks are low in nutrients and contain metals toxic to plants. But some plants have adapted to these harsh conditions over the millennia, and some grow nowhere else. Rare native plants like the Franciscan manzanita and Presidio clarkia have adapted to the serpentine soil like the kind found along these cliffs. In contrast, many invasive species have a hard time growing here, one of many reasons to protect these lands.