Geological map of Yellowstone National Park based on work by William Henry Holmes in 1878 as part of Ferdinand Vandeveer Hayden%E2%80%99s United States Geological and Geographical Survey of the Territories%2C with topography mapped by Henry Gannett and triangulation by Allen David Wilson. From the Twelfth Annual Report of the United States Geological and Geographical Survey of the Territories%3A Maps and panoramas%2C plate 6. Public Domain