Factual error: Though extremely modest on today's standards, the dress worn by Clara to the hoedown shows far too much cleavage for the time. No schoolteacher would ever wear a dress like that in the 1880s.
Factual error: In the scene after the Mandingo fight in the Cleopatra club, when Leonardo DiCaprio gives his slave a beer, it is served in a flip top bottle. The first flip-top closure was created by Charles de Quillfeldt in the United States, who filed for a patent on 30 November 1874, receiving patent number 158406.
Factual error: After the birth of the baby, James Stewart and "Doc" Witherspoon are discussing the course of the war. "Doc" relates that he has always lived in Virginia and that his son died at Gettysburg at Little Round Top. No Virginia regiments fought at Little Round Top - only Alabama, Texas, Georgia, and Arkansas regiments.
Factual error: After the first encounter with the Apaches, the covered wagon is headed to the Fort at full speed. The camera pans to the Apaches on the ridge and you can see a truck driving at the bottom right corner. (00:32:00)
Factual error: The evil man request 100,000 pieces of gold for ransom. Each gold piece looks to be about 10 ounces, and 100,000 of those would make the entire thing weigh about 31 tons, but 2 guys are carrying it around in a little chest throughout the movie.
Factual error: In the train scene near the start there are vapor trails from modern day jet aircraft in the sky above. (00:06:15)
Factual error: Towards the end when the cavalry uncovers the American flag, it has 50 stars.
Factual error: So the Civil War ends, and the colonel heads for Texas. It must have taken close to a decade to arrive there, for when he rides into Blackthorne, Texas, he's packing a Model 1873 Colt, and a Model 1873 Winchester.
Factual error: When the posse arrives at the mission, a horizontal jet stream can be seen during this scene. (01:00:00)
Factual error: In the scene just before the fight at the O.K. Corral, Wyatt is talking to his brothers and Doc on the porch of the town marshal's office. There is an American flag flying behind him with 50 stars on it when in fact there were only 38 stars on the flag in 1881.