Factual error: When Harmonica climbs down the ladder, only to meet Frank at the other end of a '45, we see that the ladder is electro-welded to the wagon and the steps are also electro-welded to the legs of the ladder - rather lousy welding seams, too! The movie takes place around 1870. Electro-welding started during the '90s, but the method got practicable only in the 1920s - and began to be commonly used in the late '30s when the great navies (except for the Royal Navy) started to use the method for their first-line ships. The great leap forward came during WW2, when Liberty ships and many other vessels were electro-welded. (01:19:50)
Factual error: As Martha is lying the table near the beginning, she is singing Danny Boy. The song was published in 1913, long after the time period of the movie.
Factual error: The camera rises up the side and over the roof of the Rail Road Office. The roof of the RR office looked like it was 100 years old. It would have leaked like a sieve all over. That RR office would have been a beautiful new building as it was on the interior scenes at that time.