Factual error: While giving Jake and Regret a tour of his hideout, the comanchero leader points out his powder mill, claiming that he gets his nitrates from his own mines, and the saltpeter from deposits to the south. If he has nitrate mines, he has no need of saltpeter.they are the same ingredient for black powder, potassium nitrate.
Factual error: Jake questions a prisoner who was recently released from Yuma Territorial Prison, a prison that would not have been constructed until 1876, 33 years in the future. As a matter of fact, the area where the town and prison would be built was, at the time period of the movie, still part of Mexico.
Continuity mistake: Jake and his prisoner arrive at the ranch where they find some dead killed by Indians. As they finish burying the people Jake's prisoner hits him with a shovel and then tosses it handle closes to him. When Jake wakes up the shovel is lying on the ground with the handle farthest away from him.