They were 600 to  long and rode atop a microplate known as the Intermontane Plate. Over early Jurassic time the Intermontane Islands and the Pacific Northwest drew closer together as the continent moved west and the Intermontane Plate subducted.
The length was 600 to long, and they rode atop a microplate known as the Intermontane Plate. Over early Jurassic time, the Intermontane Islands and the Pacific Northwest moved closer together as the continent shifted westward and the Intermontane Plate subducted.