de Fuca are remnants of headlands that remain after erosion of cliffs by wave action. Erosion of headlands creates caves, and then arches that eventually collapse to form stand-alone large or small sea stacks that lie close to the shore, and
offshore by as much as three miles. Flat-topped rocks standing at an approximate
elevation of 100 feet represent the horizontal surface of an elevated wave-cut
platform, raised by vertical movement owing to post-glacial rebound and uplift
from movement on the Cascadia subduction zone.
Thoughts by Jerry Gorsline. Photo by Olympic National Park Website.