Like Radley, I'm a big fan of HBO's Deadwood. If you feel the same, you may enjoy this link, which has some information on the historical characters the show's based on, like Calamity Jane, above. Turns out Al Swearengen was a real guy, and about as vile as the character played by Ian MacShane:"Proprietor Al Swearengen recruited women from the States, assuring them of jobs in hotels or respectable homes, and the thrill of adventure on the Western frontier. When the women arrived in Deadwood they found that they were stranded, victims of a virtual white slave trade, forced to work in abominable conditions and perform disreputable acts."
However well-grounded in actual events, the cursing strikes me as anachronistic. Not because I think cowboys talked like Jimmy Stewart. But I doubt that a certain appellation peppered throughout the dialogue was really the curse of choice in the late 19th century.
Was life on the stateless frontier really so Hobbesian? Terry Anderson and P.J. Hill have argued otherwise. But human nature being what it is, it shouldn't surprise us that the state of nature is sometimes Lord of the Flies instead of Little House on the Prairie. And that's the way it goes when the state enters the picture as well.