National Geographic Society. (2001). National Geographic guide to the national parks of the United States (3. ed., completely updated.).
Chicago-Zitierstil (17. Ausg.)National Geographic Society. National Geographic Guide to the National Parks of the United States. 3. ed., completely updated. Washington, DC, 2001.
MLA-Zitierstil (9. Ausg.)National Geographic Society. National Geographic Guide to the National Parks of the United States. 3. ed., completely updated. 2001.
Achtung: Diese Zitate sind unter Umständen nicht zu 100% korrekt.