National Geographic Society. (1978). The heart of the Grand Canyon: / Grand Canyon Park, Arizona. National Geographic Magazine.
Citazione stile Chigago Style (17a edizione)National Geographic Society. The Heart of the Grand Canyon: / Grand Canyon Park, Arizona. Washigton, Estados Unidos: National Geographic Magazine, 1978.
Citatione MLA (9a ed.)National Geographic Society. The Heart of the Grand Canyon: / Grand Canyon Park, Arizona. National Geographic Magazine, 1978.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.