APA (7th ed.) Citation

United States. National Park Service & Yard, R. S. (1921). The national parks portfolio (3rd ed.). Govt. print. off.

Chicago Style (17th ed.) Citation

United States. National Park Service and Robert Sterling Yard. The National Parks Portfolio. 3rd ed. Washington, D.C.: Govt. print. off, 1921.

MLA (9th ed.) Citation

United States. National Park Service and Robert Sterling Yard. The National Parks Portfolio. 3rd ed. Govt. print. off, 1921.