Continuity mistake: In the middle part of the film, as they look out across the field you can see the shadow of a aeroplane cross the field.
Continuity mistake: At the start when Mary gets off the buckboard she has a food basket with a couple of things but no cloth/bread, but upon entering the house the basket has a red and white check cloth and bread sticking out.
Continuity mistake: Near the beginning when Lee Van Cleef looks at the the wanted poster on the ticket booth at Tucumcari (just after getting off the train), there are two extra zero's drawn onto the poster (as added by the villain). Van Cleef then takes this poster away with him, and slots it under the door of a hotel room on a later scene - notice that the additional zero's have since disappeared from the same poster. (00:06:30 - 00:09:20)
Continuity mistake: When Oracle Jones is first sought out by the miners he drinks whiskey from a glass. As his visions grow he reaches for the whole bottle, and grabs the top to remove the cork; but the cork has already been removed.