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 seven counties in Oregon and Washington; they are Union, Umatilla, Grant, Baker, and Wallowa counties in Oregon, and Columbia and Garfield counties in Washington.