Until about 200 million years ago, the western margin of North America lay to the east, along the present Idaho border, and a broad coastal plain spread westward into Oregon. The rest of the state was ocean floor. Then the continent began moving slowly westward away from Europe and the floor of the Pacific Ocean began sliding beneath the western edge. That is what created Oregon, and Roadside Geology of Oregon tells how it happened.
"Roadside Geology of Oregon provides a handy and understandable account, either to read at home, or to carry along on trips."
– Oregon Historical Quarterly