I had never heard of this particular incident, although I knew Saint George was part of the down wind area, and there is a large cancer center there now as a result.
I found this quote in a website called "The Strait Dope." frecil Adams:
I'm horrified to have to report this, John, but your girlfriend's claim is only slightly exaggerated. Of the 220 persons who worked on The Conqueror on location in Utah in 1955, 91 had contracted cancer as of the early 1980s and 46 died of it, including stars John Wayne, Susan Hayward, and Agnes Moorehead, and director Dick Powell. Experts say under ordinary circumstances only 30 people out of a group of that size should have gotten cancer. The cause? No one can say for sure, but many attribute the cancers to radioactive fallout from U.S. atom bomb tests in nearby Nevada. ...
The movie was shot in the canyonlands around the Utah town of St. George. Filming was chaotic. The actors suffered in 120 degree heat, a black panther attempted to take a bite out of Susan Hayward, and a flash flood at one point just missed wiping out everybody. But the worst didn't become apparent until long afterward. In 1953, the military had tested 11 atomic bombs at Yucca Flats, Nevada, which resulted in immense clouds of fallout floating downwind. Much of the deadly dust funneled into Snow Canyon, Utah, where a lot of The Conqueror was shot. The actors and crew were exposed to the stuff for 13 weeks, no doubt inhaling a fair amount of it in the process, and Hughes later shipped 60 tons of hot dirt back to Hollywood to use on a set for retakes, thus making things even worse.
Many people involved in the production knew about the radiation (there's a picture of Wayne himself operating a Geiger counter during the filming), but no one took the threat seriously at the time. Thirty years later, however, half the residents of St. George had contracted cancer, and veterans of the production began to realize they were in trouble. Actor Pedro Armendariz developed cancer of the kidney only four years after the movie was completed, and later shot himself when he learned his condition was terminal.
Howard Hughes was said to have felt "guilty as hell" about the whole affair, although as far as I can tell it never occurred to anyone to sue him. For various reasons he withdrew The Conqueror from circulation, and for years thereafter the only person who saw it was Hughes himself, who screened it night after night during his paranoid last years.Wikipedia gives this version when talking about the film "The Conquerer"
The exterior scenes were shot on location near St. George, Utah, 137 miles (220 km) downwind of the United States government's Nevada National Security Site. In 1953, extensive above-ground nuclear weapons testing occurred at the test site, as part of Operation Upshot-Knothole. The cast and crew spent many difficult weeks on location, and in addition Hughes later shipped 60 tons of dirt back to Hollywood in order to match the Utah terrain and lend verisimilitude to studio re-shoots. The filmmakers knew about the nuclear tests but the federal government reassured residents that the tests caused no hazard to public health.
Director Dick Powell died of cancer in January 1963, seven years after the film's release. Pedro Armendáriz was diagnosed with kidney cancer in 1960, and committed suicide in 1963 after he learned his condition had become terminal. Hayward, Wayne, and Moorehead all died of cancer in the 1970s. Cast member actor John Hoyt died of lung cancer in 1991. Skeptics point to other factors such as the wide use of tobacco — Wayne and Moorehead in particular were heavy smokers. The cast and crew totaled 220 people. By 1981, 91 of them had developed some form of cancer and 46 had died of the disease. Several of Wayne and Hayward's relatives also had cancer scares as well after visiting the set. Michael Wayne developed skin cancer, his brother Patrick had a benign tumor removed from his breast and Hayward's son Tim Barker had a benign tumor removed from his mouth.
Dr. Robert Pendleton, professor of biology at the University of Utah, stated, "With these numbers, this case could qualify as an epidemic. The connection between fallout radiation and cancer in individual cases has been practically impossible to prove conclusively. But in a group this size you'd expect only 30-some cancers to develop. With 91, I think the tie-in to their exposure on the set of The Conqueror would hold up in a court of law." Indeed, several cast and crew members, as well as relatives of those who died, considered suing the government for negligence, claiming it knew more about the hazards in the area than it let on.