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
Stolen New Science Devices
Brimstone's local Smith and Robards representative, Albert Finley, has sent discreet word to the sheriff's office that several of his 'new science devices' were stolen last night. He needs a quiet investigation into who stole them so they can be brought to justice, and is offering $35 per person. Adventure Contact: Marshal Jon (estarrion).
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).
New Bethlehem Murder Investigation
(Likely 2 sessions) New Bethlehem, Kansas is the site of a grisly double murder and the local authorities have not been able to crack the case. A couple hired to restore an old estate were found dead, and a third man who was with them has not been found, and is suspected to be the culprit. Sleuths will be paid $40 each to solve the crime. Adventure Contact: Marshal Jon (estarrion).
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).