Paleontology and geology
Mid-Cretaceous marine ammonite and clam fossils are found east of Mt. Baker in the Cascade Range. These animals must have lived on the western edge of the North American continent before the final pieces of crust were attached as exotic terranes. Fossils of Late Cretaceous ammonites, clams, snails, and marine reptiles occur in the westernmost San Juan Islands and the adjacent Gulf and Vancouver Islands of British Columbia.