Abstract Sucia Island, part of the San Juan archipelago of western Washington, is underlain by sedimentary rocks of the Upper Cretaceous Nanaimo Group and Eocene Chucka-nut Formation (molasse). The Chuckanut overlies the Nanaimo along an important thrust fault. In addition to the geology, this trip is designed to provide excellent views of many species of sea and land birds that inhabit the offshore waters.