I just published an article in Western Folklore: “Monk, Greeley, Ward, and Twain: The Folkloresque of a Western Legend,” Western Folklore, 76:3 (Summer 2017). A quarter century ago, I published another article in Western Folklore, “Knockers, Knackers, and Ghosts: Immigrant Folklore in the Western Mines,” Western Folklore, 51:2 (April 1992). Both of these articles are available at academic.edu. These two titles might give you an inkling of the range of possibilities, but they only represent the slightest nibbling at the edge.
The problem with a lot that has been published on the folklore of the Old West is that the subject has become a catch-all for all sorts of crap that has nothing to do with folklore and little to do with anything based in reality. People make things up and pass them off in published form. In addition, the West is the largest region of the USA, and its history spans two centuries, so one needs to understand that there are many "Wests". Each location has its unique culture and oral tradition, and yet at the same time there are some overarching themes that tie the region together - more or less (often mostly less). The definitive effort to tie together the folklore and culture of the West has yet to be written.