-. (1989). Nature's wonderlands: National park of the world. National geography society.
Citazione stile Chigago Style (17a edizione)-. Nature's Wonderlands: National Park of the World. Washington: National geography society, 1989.
Citatione MLA (9a ed.)-. Nature's Wonderlands: National Park of the World. National geography society, 1989.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.