Revealing mistake: When Wyatt Earp and the actress, whom he marries later in the movie, meet on horseback, they go on a fast paced ride that concludes after going down a steep hill. If you look at the actress' feet, you will see she is riding side-saddle - a very difficult feat considering the riding they do. If you look closely you can see her real leg, safely on the other side of the horse. The side-saddle leg must be fake.
Revealing mistake: In one scene when Wyatt Earp is crying out in the middle of town and it's raining, around Wyatt, the street is soaked and puddled with pouring rain, a few feet further up the street is clearly still hard-packed dirt where the sprinklers stop - you can even see exactly where the "rain" ends.