Factual error: This movie takes place in 1850, but the "Confederate States" and "Confederate army" are mentioned. There was tension between "free" and "slave" states in 1850, but the American civil war was 11 years in the future.
Factual error: The geographical context of the film is wrong. Riverton, Wyoming (as the name implies) is in a fertile agricultural river valley. The surrounding country is uncultivated desert. There is none of the extensive grasslands shown in the film. Moreover, even in the 1960s Riverton, which is a county seat and market center, was much more substantial than the film implies.
Factual error: Captain Stanley says of Australia "What fresh Hell is this?" The scene takes place in the 1880s, yet the quote is attributed to Dorothy Parker, who would not have been born yet.