|The Pliocene Purisima Formation consists of mudstone and
siltstone beds that were deposited on a continental shelf in an oxygen-rich
environment that supported an abundant community of animals. The most common
fossils include single-celled algae (diatoms), radiolarians, and siliceous
sponge spicules. The light color of these sediments is caused, in part,
by the abundance of silica from the shells of these single-celled organisms.
In addition, fish, seal, and whalebones are abundant in the cliff faces.
Mollusk and echinoids are also rare.
The light-colored rocks reminded Sir Francis Drake of the chalk cliffs of England when he landed here in 1579.
California | Point Reyes National Seashore
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