The United States Forest Service (USFS) (defendant) and the Weyerhaeuser Company (Weyerhaeuser) entered into the Huckleberry Mountain Exchange (exchange), a land exchange authorized by the Federal Land Policy and Management Act, 43 U.S.C. § 1716. The USFS traded old-growth forest lands (forest lands) containing the ancestral grounds of the Muckleshoot Indian Tribe (tribe) (plaintiff) for land owned by Weyerhaeuser. The forest land included the Huckleberry Divide Trail (trail), a 17.5-mile historic transportation route. Section 106 of the National Historic Preservation Act (NHPA), 16 U.S.C. §§ 470-w, and a federal regulation, 36 C.F.R. § 800.5(a), required federal agencies to assess the effects of proposed undertakings on historic property. An additional regulation, 36 C.F.R. § 800.93(c)(3), authorized the use of restrictions or conditions as mitigation measures if they ensured the preservation of a property’s significant historic features. To mitigate the effects of the exchange, the USFS proposed to map and photograph the trail. The USFS rejected easements or covenants as impractical mitigation measures, because those measures required the monitoring of Weyerhaeuser’s land practices. The USFS also rejected the inclusion of conditions to prevent logging and other harmful activities. Although NHPA regulations required the USFS to consult with tribal leaders and the State Historic Preservation Officer (SHPO) to identify cultural resources, the USFS denied the tribe’s request to study additional historic sites in the forest area. The USFS justified its denial on the basis that the USFS had already conducted research in the area and that the tribe had refused to disclose information about the additional sites. The tribe sued the USFS for violating the NHPA, claiming that (1) the USFS failed to adequately consult with the tribe regarding the identification of historic sites, (2) the USFS’s mitigation measures were inadequate, and (3) the USFS failed to nominate sites to the National Register of Historic Places (register). The district court denied the tribe’s claims, and the tribe appealed.