This image depicts the two major tectonic provinces in western North America. On the west are accreted terranes of Paleozoic to Cenozoic age. Each terrane is composed of fragments of oceanic or continental material that were created somewhere away from North America, but were then tectonically accreted or attached to the western edge during subduction or translation along strike slip faults. This material built out the western edge by accreting island arcs or continental fragments translated here from far away (exotic) or close by North America (indigenous). ———————— On the Eastern half are the older passive margin sediments that were largely eroded from the eastern old part of North America and transported westward and deposited at the western edge of North America. Image courtesy of Professor Burchfiel.