Continuity mistake: When Jack Twist is chopping wood, right before Joe Aguirre visits him on his horse, he sets up a piece of wood to chop. Jack talks to Joe and when the camera pans out to show him ready to chop again, the piece of wood is gone.
Revealing mistake: During the shoot out with McGivens's gang at the Cortez ranch, the wife of Cortez sneaks out of the trap door with her baby and peers around the side of the building. You can notice that the baby is really a doll.
Factual error: Captain Stanley says of Australia "What fresh Hell is this?" The scene takes place in the 1880s, yet the quote is attributed to Dorothy Parker, who would not have been born yet.