Continuity mistake: When Abbott and Costello are on the train. Costello walks over to see the guys playing poker. In the background a man closes the back door of the train. As Costello passes you see the door is open again and the same guy closes it again. (00:17:10)
Factual error: The events depicted in the movie occur around the time of the California gold rush in 1848, yet every man and his dog wields an 1873 Colt Peacemaker.