Establishment of a peace garden and minimum altitude for aircraft flying over National Park System units : hearing before the Subcommittee on Public Lands, National Parks, and Forests of the Committee on Energy and Natural Resources, United States Senate, One hundredth Congress, first session, on S. 261 ... H.R. 191 ... S. 451 ... May 7, 1987. (U.S. G.P.O., 1987)