Here's a novel that can provide inspiration for adventures and campaigns set in the world of The Sixth Gun and Shadow Roads; it is Territory by Emma Bull.
I I first read this novel back around 2010, after a trip to the Grand Canyon, when I was starting to take an interest in supernatural westerns. Coincidentally, that was also when Oni Press released Issue #1 of The Sixth Gun for Free Comic Book Day. Here are a few of the impressions that it left on me after this second reading.
This novel is a slow burn, taking its time in building up the conflict.
It provides an interesting look at (mostly) everyday life in a small western town, which I liked.
Taking that a step further, it also provides insight into how characters can gain influence and build names for themselves and their associates, possibly leading up to a political campaign or the pursuit of other offices, such as Sheriff or Marshal.
The fire provides an excellent example of a dramatic scene that does not involve combat, but still puts the heroes in real danger.
It's an interesting take on relatively subtle magic, too, a setting in which ordinary people don't know about or believe in the occult. Some of the drama, then, comes from how they react when they see it for themselves firsthand.
Dog House Rules provides some excellent content that relates to this story, including some of the following PDFs. There's a free one that presents stats for the Earp brothers, which would need some adjustment to reflect the use of magic in this novel; the second is a comprehensive writeup for a town that was frequented by Doc Holliday and Big Nose Kate, which could be an excellent backdrop for a story like this one.