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
Rumor: Attacks on Wagon Trains
Source: Rumor that might be heard in the Diamondback Hotel & Casino, Foster's Saddle & Tack , Jumping Jack Saloon , or Silver Palace
"I had a buddy on the way up from Las Colonias heading to Raton that says he came upon a wagons in two different areas, destroyed and all torn up. The folks had been all mangled. They clearly had been bludgeoned to death, no shots fired. Equipment and stores still in the wagons, so clear won't no bandit activity. " from one cowpoke. "I've seen me what them heathen bloodthirsty Apache can do, clearly had to be them rather than some bandits." says another.
Adventure Contact: Marshal Freewolf