Washington is known as the Evergreen State because of the large number of Evergreen trees (and the significant number of days with precipitation annually). The state is bordered on the west by the Pacific Ocean, on the east by Idaho, on the south by Oregon, and on the north by British Columbia. The Cascade mountain range runs down the middle of the state, dividing it into the heavily populated western half, and the more arid less populated eastern half. Mount St Helens, a volcano that erupted in 1980, is located in western Washington, not far from the Oregon border.