In the opening chase scene between Van Heflin and the Federales (bad guys) lead by Col. Paco Ruiz, played by the father of Mickey Dolenz of the Monkees. Col. Ruiz's horse switches from a brown bay horse to a pure white horse until it trips and throws Col. Ruiz.
At 6:51 into the film, during the fight seen, Van Heflin is thrown up against what is supposed to be a rock wall, but as his back hits the wall, you can clearly see it deform from his inertia.