Other mistake: The objective of the band is a cache of gold hidden some years ago in the firebox of a wrecked locomotive in the wilds of Northern Mexico. When they finally dig the firebox door out and open it, the strongbox is sitting inside a completely clean firebox, with nary a cinder, ash, or chunk of burned wood in sight. If the loco and cars had been abandoned after the derailment, there would still have been residue in the firebox.
Factual error: Anne Margaret is seen changing into pants, and as she's shown stepping into the pant leg she is wearing white pantyhose. Pantyhose wasn't invented at this time.
Factual error: One man reaches into the fire chamber and picks up the trunk full of gold with no problem or effort. That much gold would be much heavier.