The Blues are uplift mountains and contain some of the oldest rocks in Oregon. Rocks as old as 400 million years protrude through surrounding Columbia River Basalt flows of 52 million to 6 million years ago. Geologically, the Blue Mountains are part of the larger rugged Columbia River Plateau, located in the dry area of Oregon and Washington east of the Cascade Range. They are made up of several mountain ranges, from the Ochoco and Maury Mountains in the west near Prineville, Oregon, through the Greenhorn Range and Aldrich and Strawberry Mountains, to the Elkhorn and Wallowa Mountains on the east and the Snake River in Hells Canyon. The tallest peaks are Sacajewea at in the Wallowas, Rock Creek Butte at in the Elkhorns, and Strawberry Mountain at in the Strawberry Range. There are several more 9000'+ peaks in the Wallowas, but not elsewhere in the Blues.
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.
The range is currently traversed by Interstate 84, which crosses the crest of the range at a summit, from south-southeast to north-northwest between La Grande and Pendleton. The community of Baker City is located along the south-eastern flank of the range. U.S. Route 26 crosses the southern portion of the range, traversing the Blue Mountain Summit and reaching an elevation of. It is also crossed by the Union Pacific Railroad's mainline between Portland, Oregon and Pocatello, Idaho, which crests the summit at Kamela, Oregon. The summit lies on Union Pacific's La Grande Subdivision, which runs between La Grande and Hinkle, the latter of which is the site of a major UP yard.
Wildlife
Birds of the area include bald eagle, northern spotted owl, Lewis's woodpecker, Williamson's sapsucker, red-breasted nuthatch, golden-crowned kinglet and many migratory species, with the riverbanks important habitat for this birdlife. Mammals that move through the mountain grasslands include Rocky Mountain elk, bighorn sheep and mule deer. Native fish include Chinook Salmon, Steelhead, Redband Trout, Coho Salmon, Bull Trout, and Pacific Lamprey. The Blue Mountains in Washington are home to one of 10 identified elk herds in the state, with a population of approximately 4,500 Rocky Mountain elk as of 2018 across the region. 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. By the mid 1990s the area then became known for its mature males and trophy hunting. 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. During winter months elk will prefer to use "moderately steep south slopes" rather than northern slopes because of the southern slopes being warmer and containing less snow.
The range is drained by several rivers, including the Grande Ronde and Tucannon, tributaries of the Snake, as well as the forks of the John Day, Umatilla and Walla Walla rivers, tributaries of the Columbia. The southernmost portion of the Blue Mountains is drained by the Silvies River, in the endorheic Harney Basin.