The discovery of a midget horse, thought to be of a species fifty million years old, prompts members of a Wild West show to ventureinto Mexico''s Forbidden Valley in search of world-wide fame and untold wealth. But they are met by prehistoric monsters, including"Gwangi," a giant dinosaur that decimates their ranks. Spectacular special effects from Academy Award-winner Ray Harryhausen ("Clashof the Titans," "The Beast from 20,000 Fathoms").