St. George was close enough to the NTS that they could see and sometimes hear the atmospheric tests. They were directly under the path of the debris cloud and fallout. On the Nancy Shot of the Upshot-Knothole Series (1953) Salt Lake City recorded over 10K cpm following this single test.
The John Wayne film “The Conquerer” was filmed near St. George, and tons of the dirt were brought back for scenes filmed on a sound stage. A ton of people on that movie died of cancer.
You’re absolutely correct. Many folks don’t believe me when I tell them about this. The original cause was when U.S. detonated a nuclear device from a balloon at area 49, I believe. Right next to area 51.