National parks legislation : hearing before the Subcommittee on National Parks of the Committee on Energy and Natural Resources, United States Senate, One Hundred Eleventh Congress, first session, on S. 760, S. 1838, S. 2097, S. 2722, S. 2726, S. 2738, H.R. 1849, H.R. 3689, December 3, 2009. (U.S. G.P.O.,, 2010)