Deliberate mistake: The Studebaker in which Carol is first riding bears the license number JPM 351, which interestingly enough, is not only the same license number that Steve's 58 Chevy has, but is also worn by the car Curt is sitting on when he first meets the Pharaohs. To top it off, the Edsel driven by Cindy Henderson has plates reading PRC 596, which are also used by a silver 57 Chevy and a red pickup.
Deliberate mistake: When Clint Eastwood rides into town the first time,one of the buildings has tarpaper on the outside and doesn't seem to be from the same era.This is the first and last time that building is in any shots.