The Phantom Empire
This movie is based on the movie serial . From IMDb : Cowboy singer Gene Autry stumbles upon a civilization buried beneath his own Radio Ranch. The Muranians have developed technology and weaponry such as television and ray guns. Their rich supply of radium draws unscrupulous speculators from the surface. The peaceful civilization of the Muranians is corrupted by the greed from above, and it becomes Autry's task to prevent all-out war, ideally without disrupting his regular radio show. Stars: Gene Autry, Frankie Darro, Betsy King Ross, and Dorothy Christy IMDb Page AKA Radio Ranch