Big Bend National Park Boundary Adjustment Act This bill authorizes the Department of the Interior to acquire, by donation, purchase from willing sellers, or exchange, approximately 6,100 acres of lands or interests in land generally identified as the Proposed Park Addition on the map titled Big Bend National Park, Proposed Boundary Adjustment and dated July 2020. Upon the acquisition of any lands or interests in land, Interior shall revise the boundary of the park to include the acquisition and shall administer such lands or interests in land as part of the park.