I'm in the process of writing a western feature script that is set during the twilight of the "Wild West" after the Frontier was considered closed by the Census Bureau in 1890. More specifically my story is set around 1908-1910, and a large theme I'm playing with is how products of the west (outlaws, sheriffs, etc.) are living past their prime and largely without purpose.
So my question is, what did this gradual shift in authority look like? From my understanding, sheriffs served as sources of authority in these somewhat isolated towns strewn about the west for a large part of the 19th century. Who did they answer to? From my research, I am also finding out the US Army themselves were an institutional source of authority and law. How did that power get transferred over time? How did jurisdiction overlap? How did Federal agents and US Marshals fit into all of this? How did the people of the frontier feel about the federal government coming in? The sheriffs must not have been happy about it.
Apologies about the broad question and apologies about any info I'm getting wrong, but any insight would be greatly appreciated. I would also love any and all sources on these topics.
Since you're correct that this is very broad, and also as I don't think that given you want this research for a script, I don't think that an answer written here would do you justice, so instead allow be to point you in the direction of a source I'd highly recommend. Richard Slotkin's "Gunfighter Nation: The Myth of the Frontier in 20th Century America" is exactly what you're looking for since it not only tackles questions of violence and authority, but looks at how they have entered the American mythos and been communicated to the public through portrayals in literature, film and TV, so quite pertinent for you. He breaks it into several sections, looking at how the myth of the frontier has been used in various periods of time, from the late 1890s on through the Vietnam era, and evaluating the ways that its themes have, in various ways, been molded as "surrogates" for what Americans were dealing with at the time. It's a hefty tome, but quite thorough, and well suited to giving you a better understanding of the topic at hand here, as it offers insight not only into the Frontier, but also into the META narrative of the frontier that your own script will become part of.