Grotto Geyser, Yellowstone National Park, 1935

Yellowstone National Park, established 1872, was America's first national park. Approximately two square miles in area, Upper Geyser Basin contains the largest concentrations of geysers in the park--in fact, nearly one-quarter of all the geysers in the world. Grotto, named for its interesting shape, usually erupts every two to five hours and hits heights of 20 to 30 feet.