Filming was mostly done in the Sierra de Órganos National Park in the town of Sombrerete in the state of Zacatecas, Mexico. The river and fishing lake scene was shot in the Mexican state of Durango, and some scenes were filmed at the Churubusco Studios in Mexico City. The film features stop motion animated dinosaurs constructed by Jim Danforth, including a "Tyrannosaurus Rex" which in one scene becomes intoxicated by a cannabis-type drug, animated by Randall W. Cook. Danforth was a major participant in the special effects sequences, but left the film "about two-thirds of the way" (his words) through the work because the Directors Guild of America prohibited his contracted on-screen credit, co-direction with Carl Gottlieb. Consequently, Danforth's name does not appear on the film.