APA (7th ed.) Citation

United States. National Park Service, Yard, R. S., & Story, I. F. (1931). The national parks portfolio (6th ed.). U.S. Govt. Print. Off..

Chicago Style (17th ed.) Citation

United States. National Park Service, Robert Sterling Yard, and Isabelle F. Story. The National Parks Portfolio. 6th ed. Washington: U.S. Govt. Print. Off., 1931.

MLA (8th ed.) Citation

United States. National Park Service, et al. The National Parks Portfolio. 6th ed. U.S. Govt. Print. Off., 1931.

Warning: These citations may not always be 100% accurate.