The boundaries of Big Bend National Park, established by the Act of June 20, 1935 (16 U.S.C. 156), are hereby revised to include the lands and interests therein, together with all improvements thereon, within the area comprising approximately sixty-seven thousand one hundred and twenty-five acres as generally depicted on the map entitled "Harte Ranch Addition, Big Bend National Park", numbered 155/80,044 and dated September 1987. Such map shall be on file and available for public inspection in the offices of the National Park Service, Department of the Interior. The Secretary of the Interior is authorized to acquire lands and interests therein, together with all improvements thereon, within the addition described in such map by donation, purchase with donated or appropriated funds, or exchange.