Geologic History

Cordell Bank National Marine Sanctuary is situated on the Pacific Plate and Cordell Bank is the most prominent geological feature rising above the seafloor in the sanctuary.

The Salinian bedrock of Cordell Bank formed about 100 million years ago as part of the southern Sierra Nevada mountain range. In the last 33 million years, the Pacific Plate moved north, sheared off part of the North American plate and carried Cordell Bank to its present location west of Point Reyes. The bank continues to move north at a rate of about five centimeters per year.

Between 20,000 and 15,000 years ago when sea level was about 360 feet below current sea level, most of Cordell Bank was exposed, making it a true island. Today, the sediments surrounding the base of Cordell Bank on the continental shelf are composed predominantly of silt and sand deposits that originated from rivers and coastal erosion.

For more information on the geology within Cordell Bank Sanctuary and the research being conducted on this topic, please visit the Sanctuary Integrated Monitoring Network (SIMoN).