The 'slickers' worn (long coats) show button clasps that were not invented until well into the 20th century.
During a bank robbery, the female cashier/teller has obvious artificial fingernail extensions, which did not exist until 1954.
The buttons on the shirts show 4 holes, as opposed to just Two..... 4 holed buttons did not exist/appear until well into the 20th century.
As the train steams along around the 20 minute mark, you can see an electrical switch box which did not exist at the time of this movies setting.
A cowboy can be seen in a bar drinking from a very obvious Grolsh beer bottle with the flip lid that did not exist until 1897, and the liquid within is so pale, it is clearly not beer.
In the bar, the liquor bottles on the shelf are all empty.
None of the guns when fired in this movie show any recoil.... The smoke from expired shots is minimal and obviously not black powder. Smokeless gun powder was not invented until 1884 and distribution was minimal until years later.