When Murietta finds the statue in the hidden compartment of the coach he scrapes it with his gun to reveal gold. After the others gather and look in the coach there is no mark on the Madonna.
During the showdown between Murietta and Clay in the wide shots the sky is dark blue but in the closeup of Murrietta the sky behind him is pitch black.
At 1:08:10 - 16 on the Youtube version, there is showing in the upper left hand corner of the screen a modern dam/ weir construction that wouldn't be built for another 100 years approximately from the 1840s.
The movie is supposedly set in the late 1840's, but the first scene in the film shows the characters played by Ricardo Montebaln and Earl Holliman using a Winchester repeating rifle and a repeating revolver, respectively, neither one of which were developed or produced for more than another ten years.