Pacific Northwest National Scenic Trail Act of 2008 - Amends the National Trails System Act to designate the trail extending from the Continental Divide in Glacier National Park, Montana, to the Pacific Ocean coast in Olympic National Park, Washington, as the Pacific Northwest National Scenic Trail.
Requires the Trail to be administered by the Secretary of Agriculture.
Bars the United States from acquiring land or interest in land outside the exterior boundary of any federally-managed area for the Trail without the owner's consent.