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The Blue Mountains are a mountain range in the northwestern United States, located largely in northeastern Oregon and stretching into extreme southeastern Washington. The range has an area of about 15,000 square miles (38,850 km2), stretching east and southeast of Pendleton, Oregon, to the Snake River along the Oregon–Idaho border.[2]
The Blue Mountains cover nine counties across two states; they are Union, Umatilla, Grant, Baker, and Wallowa counties in Oregon, and Walla Walla, Columbia, Garfield and Asotin counties in Washington.[3] They are unique as the home of the world's largest living organism, a subterranean colonial mycelial mat of the fungus Armillaria ostoyae.[4] The Blue Mountains were named after the color of the mountains when seen from a distance.[5]