Offshore and beneath Del Norte’s forest lies a mixture of twisted rocks. Over 20 million years, more than eight miles of sandstone, shale, serpentine, chert, and greenstone (a blend called Franciscan Complex) have built up in layers from the original ocean floor. These sediment layers resulted from repeated tectonic plate collisions. Three tectonic plates—North American, Pacific, and Gorda—all meet offshore at the Mendocino Triple Junction south of Eureka. Particles from each plate collision float along the ocean floor until they are deposited. Sea stacks—rock towers that have broken off from the main land mass—protrude from offshore waters.

For more information about geology in Redwood National and State Parks, go to the National Park Service website.