Boulder River Wilderness is a federally protected area in northwest Washington's western Cascades within Mount Baker-Snoqualmie National Forest. Encompassing 48,674 acres around the Boulder River, it ranges from low valley forest to the 6,850-foot south peak of Three Fingers, linked by a jagged ridge with summits such as Liberty, Big Bear, Whitehorse, Salish, and Buckeye. The wilderness contains old-growth Douglas fir, hemlock, cedar, and other species, including rare lowland virgin forest along the river. Boulder River drains the area's northwestern section, wildlife includes bears, deer, elk, and mountain goats, and although trails enter the margins, the central core remains rugged and mostly trailless.