This movie is scripted by Willis O'Brien ,who obviously thought so much of it ,that he used it again in 1969 for the superior The Valley of Gwangi It is a curiosity among movies, being a science fiction and Western hybrid .Mexican based rancher Jimmy -woodenly played by Guy Madison -believes that his dead cattle are the result of predators .He is thinking "Mountain lion " or "coyote " maybe .Wrong!Its a T-Rex and the pattern then follows the standard monster movie template -capture and escape ,rampage and eventually happy ever after resolution . The monster effects are okay for the era but completely overshadowed by the genius of Ray Harryhausen ,employed in the remake .Add somewhat muddy colour and you have a movie whose technical side is deficient by today's standards It still remains worth watching however if only for its being such a rare commodity in combining monster movie and Western