August 17

1870 On August 17, 1870, Ferdinand Vandeveer Hayden and his exploration party visited the Natural Bridge, now known as Ayres Natural Bridge.

1959 An earthquake occurred at Hebgen Lake near West Yellowstone, Montana. It was a 7.5 on the Richter Scale. The tremors shook all of Yellowstone National Park and quite a lot of Montana, Wyoming, and Idaho.