Voice specialist Paul Frees is given credit for special voice effects. His contributions included the vocal sounds of the cyclops, the breathing sound of the giant lizard and the "Mexican" voice heard on the plane's radio.
Though much of the action takes place in two different canyons, all scenes for both were shot in the fabled Bronson Canyon; the famous cave was used in the "second" one. Bronson Canyon was where The Texas Rangers were ambushed in The Lone Ranger. The cave in Bronson Canyon served as the exterior of the Batcave in the 1966 Batman television series
Originally set to be released by RKO Radio Pictures, but sold to Allied Artists when RKO shut down their distribution arm.
The cyclops myth almost certainly originated in the Greek islands, which in prehistoric times were the home of dwarf mastodons. By the classical period they were all extinct, but their jumbled bones could be found in caves (and still are). Like the modern elephant, the skull has a central opening for the nasal passage of the trunk, which resembles a human eye socket, whereas the real sockets are further back and rather indistinct - thus it looks like the skull of a giant man with one eye.
The facial prosthetic work of THE CYCLOPS and 1957's WAR OF THE COLOSSAL BEAST are strikingly similar to each other, perhaps because the same makeup artist, Jack H. Young, created them both back to back.