Blue Mountains, uplifted, eroded part of the Columbia Plateau, c.6,500 ft (1,980 m) high, NE Oreg. and SE Wash. Lava flows cover much of the surface. The upper, wooded slopes are used for lumbering. Recreation and livestock grazing are the mountains' principal economic uses. Rock Creek Butte, 9,105 ft (2,775 m) high, is the highest point in the Blue Mts. The Blue Mountains were a major physical obstacle for those who once traveled the Oregon Trail.