To amend the National Trails System Act to clarify Federal authority relating to land acquisition from willing sellers for the majority of the trails in the System, and for other purposes.

National Trails System Willing Seller Act - Amends the National Trails System Act to: (1) prohibit the Government acquisition of lands outside the exterior boundaries of any federally administered area, except with the owner's consent, for the Oregon, Mormon Pioneer, Lewis and Clark, Iditarod, and Nez Perce National Historic Trails and the Continental Divide, North Country, Ice Age, and...