Washington is a state in the Pacific Northwest region of the United States located north of Oregon, west of Idaho, and south of the Canadian province of British Columbia on the coast of the Pacific Ocean.
Washington is the north-western most state of the contiguous United States. Its northern border lies mostly along the 49th parallel, and then via marine boundaries through the Strait of Georgia, Haro Strait and Strait of Juan de Fuca, with the Canadian province of British Columbia to the north. Washington is bordered by Oregon to the south, with the Columbia River forming the western part and the 46th parallel forming the eastern part of the southern boundary.
To the east, Washington borders Idaho, bounded mostly by the meridian running north from the confluence of the Snake River and Clearwater River (about 116°57' west), except for the southernmost section where the border follows the Snake River. To the west of Washington lies the Pacific Ocean. Washington was a Union territory during the American Civil War, although it never actually participated in the war.
Washington is part of a region known as the Pacific Northwest, a term which always includes Washington and Oregon and may or may not include Idaho, western Montana, northern California, and Alaska, depending on the user's intent.
The high mountains of the Cascade Range run north-south, bisecting the state. From the Cascades westward, Western Washington has a mostly marine west coast climate, with mild temperatures and wet winters, autumns and springs, and relatively dry summers. Western Washington also supports dense forests of conifers and areas of temperate rain forest. These deep forests of the Olympic Peninsula, such as the Hoh Rainforest, are among the only temperate rainforests in the continental United States.
In contrast, Eastern Washington, east of the Cascades, has a relatively dry climate with large areas of semiarid steppe and a few truly arid deserts lying in the rainshadow of the Cascades; the Hanford reservation receives an average annual precipitation of 6 to 7 inches (150 to 180 mm). Farther east, the climate becomes less arid, increasing as one goes east to 21.2 inches (540 mm) in Pullman. The Palouse southeast region of Washington was grassland that has been mostly converted into farmland. Other parts of eastern Washington are forested and mountainous.
Washington also is home to several other mountain ranges, the most prominent of which are the Olympic Mountains, far west on the Olympic peninsula; the Kettle River Range in the northeast; and the Blue Mountains in the southeast. The Cascade Range contains several volcanoes, which reach altitudes significantly higher than the rest of the mountains.
From the north to the south these volcanoes are Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams. Mount St. Helens is currently the only Washington volcano that is actively erupting; however, all of them are considered active volcanoes. Mount Rainier, the tallest mountain in the state, is 50 miles (80 km) south of the city of Seattle, from which it is prominently visible. The 14,411-foot-tall (4,392 m) Mt. Rainier is considered the most dangerous volcano in the continental U.S., due to its proximity to the Seattle metropolitan area and is similarly listed as a Decade Volcano. It is also covered with more glacial ice than any other peak in the lower 48 states.