The Pacific Northwest, also referred to as Cascadia, is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common conception includes the U.S. states of Oregon, Washington, and Idaho and the Canadian province of British Columbia. Some broader conceptions reach north into Alaska and Yukon, south into Northern California, and east into western Montana. Other conceptions may be limited to the coastal areas west of the Cascade and Coast mountains.