The Cyclops [1957 - USA] sci fi

Susan Winter has arranged for an expedition to the remote jungles of Mexico to locate her fiance, Bruce Barton, whose plane crashed three years ago, she certain in her heart that he is still alive. The other three in the expedition filling the four seater prop plane are: pilot Lee Brand; Susan and Bruce's friend, bacteriologist Russ Bradford, whose goal unknown to her is to put to rest the idea that Bruce is still alive in he being in love with her himself; and shady geologist Marty Melville who, partially financing the expedition with what Susan could not finance herself, is on his own mission to locate what he is suspects is a lucrative deposit of uranium in the area. What Susan has not received is the authority of the state's Governor, who does not trust the motives of most in the party, especially Marty's, and has directed one of his own men onto the plane to ensure the party returns to the States and does not make the expedition. Ignoring the Governor's order, Susan, Russ, Lee and Marty do go on the expedition as planned. Beyond Marty trying to work solely toward his own goal as the Governor had feared as Marty does find evidence of the uranium, what affects the mission is they finding the area being populated with giant animals, such growth which could not occur under normal circumstances, something that Russ the scientist would like to study. But it is one of those "beasts" which will give at least Russ some certainty as to what happened to Bruce.