Factual error: During the scene towards the end of the film where Alejandro is chasing Captain Love in the shack with the furnace at the mine, we see a pressure gauge just before the furnace explodes. The unit of measurement on the pressure gauge is shown as kg/cm2. Metric measures were not used in Mexico until eleven years after the film was set, and as California was a part of Mexico at the time, metric measurements would not have been used there.
Factual error: The film takes place during the 1840s and features an American Army officer, Capt. Love. The western style hat that Love wears with the crossed swords insignia of the infantry was not used by the US Army until the American Civil War, twenty years later. During the time period of the film, US Army officers wore a soft cap with a bill in front.