Factual error: In the drugstore scene where Mary whispers in George's bad ear, there are several shots showing a Coca-Cola thermometer on the wall where George hangs his jacket. This particular scene was to have taken place in 1919, but this particular thermometer wasn't produced until 1939.
Factual error: Tombstone is nowhere near Monument Valley.
Factual error: Fred would not have been a captain without prior college education. He was previously a soda jerk and would have been enlisted.