The Blue Mountains are a mountain range in the western United States, located largely in northeastern Oregon and stretching into southeastern Washington. The range has an area of 4,060 square miles (10,500 km2), stretching east and southeast of Pendleton, Oregon, to the Snake River along the Oregon-Idaho border. The Blue Mountains cover eight counties across two states; they are Union, Umatilla, Grant, Baker, and Wallowa counties in Oregon, and Walla Walla, Columbia and Garfield counties in Washington. They are home to the world’s largest organism and fungal mycelial mat, the Armillaria ostoyae. The Blue Mountains were so named due to the color of the mountains when seen from a distance.