40 C.F.R. § 81.400
Subpart D, §§ 81.401 through 81.437 , lists those mandatory Federal Class I areas, established under the Clean Air Act Amendments of 1977, where the Administrator, in consultation with the Secretary of the Interior, has determined visibility to be an important value. The following listing of areas where visibility is an important value represents an evaluation of all international parks (IP), national wilderness areas (Wild) exceeding 5,000 acres, national memorial parks (NMP) exceeding 5,000 acres, and national parks (NP) exceeding 6,000 acres, in existence on August 7, 1977. Consultation by EPA with the Federal Land Managers involved: The Department of Interior (USDI), National Park Service (NPS), and Fish and Wildlife Service (FWS); and the Department of Agriculture (USDA), Forest Service (FS).
40 C.F.R. §81.400