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: This movie takes place in 1850, but the "Confederate States" and "Confederate army" are mentioned. There was tension between "free" and "slave" states in 1850, but the American civil war was 11 years in the future.
Factual error: In the first scene, McGivens appears and demonstrates the new repeating rifle, and even mentions that it is a Henry Repeater. This brand of rifle was not invented until the late 1850s, almost a decade after the events depicted in this movie.