National parks bills [electronic resource] : hearing before the Subcommittee on National Parks of the Committee on Energy and Natural Resources, United States Senate, One Hundred Thirteenth Congress, first session, on S. 59, S. 155, S. 156, S. 219, S. 225, S. 228, S. 285, S. 305, S. 349, S. 371, S. 476, S. 486, S. 507, S. 615, April 23, 2013.
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