This case arises out of the Forest Service's decision to issue a special use permit authorizing the development of a major destination alpine ski resort at Sandy Butte in the North Cascade Mountains. Methow Recreation, Inc. (MRI), applied for a special use permit to develop and operate its proposed 'Early Winters Ski Resort' on Sandy Butte and a 1,165-acre parcel of land it had acquired adjacent to the National Forest. The Forest Service, in cooperation with state and county officials, prepared an EIS known as the Early Winters Alpine Winter Sports Study (Early Winters Study or Study). The stated purpose of the EIS was 'to provide the information required to evaluate the potential for skiing at Early Winters' and 'to assist in making a decision whether to issue a Special Use Permit for downhill skiing on all or a portion of approximately 3900 acres of National Forest System land.' The Study concluded that, although the construction, maintenance, and operation of the proposed ski area 'will not have a measurable effect on existing or future air quality,' the off-site development of private land under all five alternatives -- including the 'no action' alternative -- 'will have a significant effect on air quality during severe meteorological inversion periods.' The EIS identified actions that could be taken by the county government to mitigate the adverse effects of development, as well as those that the Forest Service itself could implement at the construction stage of the project. The EIS concluded that no endangered or threatened species would be affected by the proposed development and that the only impact on sensitive species was the probable loss of a pair of spotted owls and their progeny. The Washington Department of Game voiced a special concern about potential losses to the State's largest migratory deer herd, which uses the Methow Valley as a critical winter range and as its migration route. The Regional Forester recommended the permit. Four organizations opposing the decision to issue a permit appealed the Regional Forester's decision to the Chief of the Forest Service. After a hearing, he affirmed the Regional Forester's decision. Stressing that the decision, which simply approved the general concept of issuing a 30-year special use permit for development of Sandy Butte, did not authorize construction of a particular ski area and, in fact, did not even act on MRI's specific permit application, he concluded that the EIS' discussion of mitigation was 'adequate for this stage in the review process.' Respondents brought this action under the Administrative Procedure Act, 5 U.S.C. §§ 701-706, to obtain judicial review of the Forest Service's decision. The Magistrate noted that additional mitigation strategies would be included in the master plan, that the Forest Service continues to develop mitigation plans as further information becomes available, and that the Regional Forester's decision conditioned issuance of the special use permit on execution of an agreement between the Forest Service, the State of Washington, and Okanogan County concerning mitigation. The Court of Appeals reversed. The court held that the Forest Service could not rely on 'the implementation of mitigation measures'' to support its conclusion that the impact on the mule deer would be minor, 'since not only has the effectiveness of these mitigation measures not yet been assessed, but the mitigation measures themselves have yet to be developed.'