The Pacific Northwest extends from southeastern Alaska to Northern California. Along this entire length, is a large mountain range, the Cascade Range, that forms the geographic spine of the Pacific Northwest. The highest mountain in the Northwest is Mount Rainier. Rainier is high. Other notable mountains include Mount Shasta, at , and Mount Baker, at . East of the Cascades, there is the Columbia Plateau, a high area of land that stretches east to the Rocky Mountains in Idaho and Montana. In the west, the Coast Range borders the coast more closely. The Olympic Mountains are on the Olympic Peninsula, an extension of Washington State. Puget Sound is a large system of bays and straits in northwestern Washington and southeastern British Columbia.