The Valley of the Gwangi is a curious mix of the western and science fiction genres. In it, a cowboy named Tuck (James Franciscus) vies to capture a wild Tyrannosaurus Rex with the intentions of procuring monetary gain by putting the wild beast on display in a Mexican circus. To do this, he must venture into the Forbidden Valley, against the advice of his peers. In this untouched land, he will confront much adversity and danger as he attempts to capture this prehistoric creature. He is also after a creature known as the Gwangi. This is a primeval horse so tiny that it is thought to be the smallest in the world. In addition to financial gain, Tuck aims to win the love and affection of TJ (Gila Golan) with this dangerous endeavor. Other cast members include Professor Bromley (Lawrence Naismith) and Tia Zorina (Freda Jackson), as well as Carlos (Gustavo Rojo).