Factual error: Tonto explains to a boy how he showed two men the location of rich silver deposits in exchange for a cheap watch from Sears Roebuck. The scene is to have taken place when Tonto was child, which would be several years prior to 1869, when Tonto was an adult. However, Sears Robuck was not founded until 1886, many years after the story could have taken place.
Continuity mistake: At the start of the train chase the woman falls off the side of the steam engine - it cuts to the bad guy standing at the front on the cow catcher and he shouts "get me close." The other bad guy speeds up the train - it cuts to Tonto looking at the train and we see the bad guy climbing down onto the cow catcher, despite already standing on it in the earlier shot.
Continuity mistake: When the woman is dropped off the train and lands on silver the area next to the railway track is all clear, but immediately before and after it's all woodland up to the track.
Revealing mistake: In each one of his scenes, every time you see Captain Fuller you can see that the actor is wearing contacts to make his eyes blue. It's obvious contacts with the brown rings of his natural eyes around them. And contacts were not invented for a long long time after this movie takes place.