Several hillsides around San Francisco Bay held enough nuclear firepower during the Cold War to help carry out World War III.
Technically, WWIII would already have been underway when these missiles were launched – they were part of a last line of defense against nuclear-armed Soviet bombers headed our way.
Check out Craig Miller's wonderful Bay Curious interview with two of the "missile men" who helped operate a missile battery in the Marin Headlands.
If just one of the nuclear-tipped Nike Ajax or Hercules missiles had been launched to intercept an approaching bomber, as it detonated overhead it would have vaporized everything within a radius of about 30 miles.
(The young Air Force guys who ran the various missile batteries around the Bay knew they would have approximately 30 minutes to live after launching a missile, and we can only assume the same would have been true for millions of civilians nearby.)
Many of the hilltops around us are where the idea of "mutual assured destruction" was to be put into practice.