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 , stretching east and southeast of Pendleton, Oregon, to the Snake River along the Oregon–Idaho border.
The Blue Mountains cover ten counties across two states; they are Union, Umatilla, Grant, Baker, Wallowa and Harney counties in Oregon, and Walla Walla, Columbia, Garfield and Asotin counties in Washington. The Blue Mountains were named after the color of the mountains when seen from a distance and the blue hue imparted by the smoke of forest and range fires set by Indigenous people as management tools in the fall.
The Blue Mountains are unique as the home of the world's largest living organism, a subterranean colonial mycelial mat of the fungus Armillaria ostoyae.
Geography
The Blue Mountains include several mountain ranges, from the Ochoco Mountains and Maury Mountains in the west near Prineville, Oregon, through the Greenhorn Mountains, the Aldrich Mountains, and the Strawberry Range, to the Elkhorn Mountains. The tallest peaks are Rock Creek Butte at in the Elkhorn Mountains, and Strawberry Mountain at in the Strawberry Range. and contain some of the oldest rocks in Oregon. Rocks as old as 400 million years protrude through surrounding Columbia River Basalt flows and related volcanics of 16.7 million to about 6 million years ago.
Geologically, the oldest rocks of the Blue Mountains (400+ to about 150 million years in age) were created as island arcs in the Pacific Ocean and accreted onto the North American plate.
thumb|right|upright|Meadow in the [[Elkhorn_Mountains_(Oregon)|Elkhorn Mountains]]
The ranges of the Blue Mountains were uplifted by folding upward into the "Blue Mountain Anticline" by tectonic rotation that began about 14 million years ago. More limited faulting and extension in places that include Baker valley and the Grande Ronde valley also contributed to today's topography. The Wallowa Mountains are considered to be part of the Blues by many geologists because their geology includes the same accreted terranes as the Elkhorns, Greenhorns, and Strawberries, although their mechanism of uplift differs somewhat. Similarly, the geology of Hells Canyon and the Seven Devils Mountains is also composed of accreted terranes of a similar nature.
History
Habitation by Native Americans
The river valleys and lower levels of the range were occupied by indigenous peoples for thousands of years. Historic tribes of the region included the Walla Walla, Cayuse people and Umatilla, now acting together as the Confederated Tribes of the Umatilla Indian Reservation, located mostly in Umatilla County, Oregon. The southern portion of the Blue Mountains were inhabited by several different bands of the Northern Paiute, a Great Basin culture. Native American tribes originally migrated to the Blue Mountains for hunting and salmon runs. The Natives used to purposefully burn small parts of the forest in order to create pastures to attract game for hunting. In 1989, in response to a decline in the elk population and a heavy female-biased population, the Washington Fish & Wildlife Department regulated elk hunting in the Washington Blue Mountains with a "spike-only" general hunting season, permitting hunting of only male elk with at least one visible non-branched antler. In 2018, Washington State proposed an updated elk management plan intended to improve the health of elk populations and habitats, reduce human conflict and agricultural damage, and managing elk populations for recreational, educational, scientific, and ceremonial purposes.