I can tell how much research went into this and it's brilliant! God, you know how people will go like "We don't have diversity because it didn't exist back in the Wild West"? You're showing them how good writing looks like! And thanks a ton for the links!
But it's literally historically accurate! Mestizo, Black, Indigenous and I believe Chinese people made up most of the cowboys and cowgirls (because records show women drove cattle and helped or ran some ranches) of the era. I know white cowboys are the "norm" no thanks in part to spaghetti westerns and early western movies. Also much to the surprise of people social trail life was surprisingly egalitarian they shared sleeping quarters and blankets this doesn't mean they didn't face discrimination they did, it is after all the 1800s :/. I live for dispelling this sort of thing tbh.
Sources to check out: https://www.blackpast.org/global-african-history/perspectives-global-african-history/cowboys-color-south-america/
The Cowboy Encyclopedia by Richard Slatta there's previews available
http://www.scholastic.com/browse/article.jsp?id=4807