For West Marches style to truly be effective it requires agency and active participation from the players.
To that end, the players need to know some of the things going on near Brimstone, rumors that have been heard, bounties and notices posted, strange locales hinted at etc. This is an available collection of those that have been found.
This is by no means exhaustive. Consult with Marshals for further possibilities, including ones you might have.
Open Adventure Hooks
Cattle Drive to Wyoming
(3 sessions) Telegram from Bill Sutter: "Hey there gents and ladies, I sure do appreciate all of your help taking my cattle from Texas to Denver! Things have changed in the market, and I plan to take my herd and another I got for cheap up to Wyoming and setup a ranch there. The trail is as dangerous as always, so I could use a hand with some study cowhands or those good with a gun! Meet me in Denver if you're interested in another trail ride, I'm offering $50 per month." Adventure Contact: Marshal Jon (estarrion). Tags: Riding, Survival, Horror, Moderate Roleplay, Heavy Combat. Content Warning: Violence, Gore.
Possession in Las Cruces
Rumors have spread that a young boy in Las Cruces, New Mexico has been possessed by a demon. Doctors and local authorities are stumped, and have offered a $200 reward for dealing with the problem. Adventure Contact: Marshal Jon (estarrion). Tags: Investigation, Occult, Horror, Heavy Roleplay, Some Combat. Content Warning: Child in Danger.
Red Skies and Dead Lands
(1+ session?) Red skies and ill winds blowing from northwest of Brimstone have folks who live on the outskirts worried. A former protégé of Darius Hellstrome has found a way to use the Hunting Grounds to directly power his weird science "advances", but at what cost? The Texas Rangers are looking for stern-willed troubleshooters who may have to look the Devil in the eye and shut down the source of this trouble. They'll owe Brimstone a favor. Adventure Contact: GM Deanopalooza. Tags: Survival, Horror, Weird Science, Moderate Roleplay, Combat. Content Warning: Violence, Gore.