Section 476 of the Organic Act of 1897 (Act), 16 U.S.C. § 476, authorized the secretary of agriculture to sell only the “dead, matured, or large growth of trees” in national forests, in order to promote younger forest growth. Section 476 also required timber to be marked and designated prior to being sold. The United States Forest Service (USFS) (defendant) entered into three contracts for the sale of timber in the Monongahela National Forest (Forest), which was located in West Virginia. The contracts involved the sale and cutting of trees that were not dead, physiologically mature, or large. Also, the trees were not marked prior to cutting. The West Virginia Division of the Izaak Walton League of America (plaintiff) brought an action against the USFS, challenging the timber sales and seeking declaratory and injunctive relief. The district court enjoined the USFS from contracting for or allowing tree cutting in the Forest in violation of the Act. The USFS appealed, claiming that “large growth of trees” referred to the number of trees rather than the size of the trees. The USFS also claimed that “mature” referred to (1) physiological maturity; (2) economic maturity, or the highest marketable value; and (3) management maturity, or the point at which a tree best fulfilled its purpose of supplying a product.