Although her novels are set in Wyoming, Margaret Coel lives in Colorado. Still, much of what I will say applies to her works too.
1. The Protagonist. The idea of the "wounded detective" is common. Fictional dectectives are often divorced, widowed, deeply depressed (especially in Scandanavia), using or recovering from too much booze & drugs, or fired from a job in law-enforcement, among other possibilities. Coel's Catholic mission priest, John O'Malley, a recovering alcoholic, is isolated by both his clerical vocation and his location on the Wind River Reservation.
Often they are marginalized in some respect. Bowen's Metis brand inspector-deputy sheriff, Gabriel Du Pré, is Métis, descended from the French/indigenous mixed-blood ethnic group who originated around the Great Lakes, but some of whom moved to eastern Montana in the 1860s–70s, before and after the Red River Rebellion. Father O'Malley is a white priest on the reservation, while Box's Joe Pickett is frequently in conflict with his superiors in the Wyoming Game & Fish Department.
2. The Milieu. A low population is essential. Gabriel Du Pré operates in a fictional locale somewhere north of Miles City. Johnson's Sheriff Longmire patrols the thinly populated fictional Absaroka County, somewhere in northern Wyoming, not far from the district where Box's game warden protagonist, Joe Pickett, enforced wildlife laws.
The Wind River Reservation's population exceeds 40,000, thinly spread, but you do not feel their presence in the novels. Sean Shanahan, McCafferty's artist-fishing guide amateur detective, pops into Ennis, West Yellowstone, and other towns, but spends more time on the rivers.
All seem allergic to cities. Gabriel Du Pré hates going to Bozeman, while Joe Pickett regards Cheyenne as just slightly better than Mordor.
3. The "Animal Helper." Although several protagonists often have a dog riding with them, what I mean here is the old folkloric theme of the animal who establishes a special relationship with the hero — for example, the hero is a hunter pursuing a fox, but he spares the fox who then protects him or helps him to secure wealth.
I extend the term "animal helper" to include people who are bonded to the hero somehow yet also appear to be closer to nature — even feral. (The Hollywood equivalent is the Magical Negro, another version of the Noble Savage.)
- Gabriel Du Pré has Beneetse, an elderly Crow (?) shaman who appears and disappears mysteriously and who brings past and present together. (His name probably comes from someone mentioned in Dan Cushman's The Great North Trail, one of Bowen's source books.)
- Joe Pickett's feral helper is the falconer Nate Romanowski, a mysterious ex-special operations soldier who lives in isolated places and has no visible means of support, but who pops up in the nick of time of save Joe, dropping bad guys at 800 yards offhand with a .454 Casull revolver or something similar. For a time Romanowski lives with an Arapaho woman until she is murdered.
- Father O'Malley has Vicky Holden, the Arapaho lawyer who connects him with the reservation and its people.
- Sheriff Walt Longmire's closest friend is Henry Standing Bear, a Cheyenne. Although Lou Diamond Phillips ably portrays Standing Bear in the TV series, in the books Standing Bear is more like Beneetse — in touch with ghosts and ancestors and also seemingly able to materialize, like Nate Romanowski, when Longmire is in desperate straits.
- McCafferty's detective, Sean Stranahan, has no Indian helper, but possibly the fishing outfitter Rainbow Sam, Sean's sometime employer, could fit the bill, for by comparison to the past-haunted hero, Sam is hard-drinking, pleasure-seeking, and present-oriented.
- The Cult. Clearly inspired by the Church Universal and Triumphant's operation north of Yellowstone Park in the 1980s, this plot has some mysterious but well-financed group building a headquarters in an isolated area. Murder usually ensues. See also "The Anti-Government Group." C. J. Box in particular shows some degree of sympathy with small-L libertarian types, however, which leads to some plot twists.
- The Evil Energy Company. Enough said. See also "Evil Rich People."
- The Scheming Archaeologist. No, Tony Hillerman did not own this one. Suppose that an archaeologist had a major, career-capping find that somehow places him in conflict with the Native American Graves and Repatriation Act. . .
- Ecoterrorists and Animal Rights Extremists. They mean well, but people get hurt and they are trying to shut down the struggling local ranchers.
- The Dinosaur. Inspired by the story of the T-Rex skeleton called Black Hills Sue, this one involves a spectacular fossil find with disputed ownership — various people want to profit from it. It puts the "skull" in skullduggery.
- The Outsiders. All these people want to ruin Wyoming or Montana, and the hero fights a rear-guard action. Peter Bowen is the strongest here, sending a message to his readers that might as well read, "You readers are a bunch of Subaru-driving, Patagonia-wearing recreationists who just ought to keep the hell out of eastern Montana. Don't come here. Don't look for a real Gabriel Du Pré. Just stay on Interstate 90 and keep going to Bozeman. Oh yeah, buy my books."