It was August, 1959. Boise was having one of its typical hot, dry summers. A fire had just burned 9,000 acres in the nearby foothills. Then on August 20, a huge storm system dumped heavy rain on the Treasure Valley. One inch of rain fell in an hour on the burn scar.
The water overwhelmed the hills and washed away tons of topsoil. A Forest Service video made several years after the event, tells the story.