Revealing mistake: Although the film is set during the aftermath of the Mexican War (1848-50), the mountain vistas display some lovely radio towers and fire ranger stations.
Other mistake: During the ‘rescue' mission to save the trapped wagon train, none of the riders are carrying packs of food or any supplies. One man is carrying a military unit banner on a pole. Unrealistic for this type of activity.
Continuity mistake: Jeremiah Johnson acquires two horses at the beginning of the movie, one completely black, and one almost completely brown. A few minutes later, Jeremiah Johnson is seen riding a horse that is different than the two he just acquired. The new horse is distinguished by his near entirely white face. (00:07:20)