Big Thompson Flood, July 31, 1976

From the Fort Collins Coloradoan (Jason Pohl):

All told, Colorado’s deadliest natural disaster claimed 144 lives, injured scores of others, and permanently altered memories and landscapes alike. It prompted new talks about living in flood country and became the “where were you” moment for a generation, ranking alongside Dec. 7, 1941, and Sept. 11, 2001.