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
Twilight Protocol: Famine at Bell Ranch Ranch
Owner Wilson Waddingham has discreetly contacted the Territorial Rangers to let them know that soon after the Hawley Gang was booted from the ranch, the entire region has been suffering from a sickness that causes both plant and animal to waste away. Waddingham's prize cattle, worth over $20 a head, along with all of the staff at the ranch are in danger of starving to death in the next couple of weeks unless something can be done. Adventure Contact: Marshal Jon (estarrion).
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
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).
Colfax County Range War
The Maxwell Land Grant has displaced many people in northern New Mexico, causing a range war to rage on in Colfax County for over ten years. Recently, two small prospector operations near Folsom, NM are close to a mine and have both claimed ownership. Things have gotten much worse since Ghost Rock was discovered there, leading to jealousy and outright violence between the two groups. Local law has been overwhelmed and has asked for troubleshooters to intervene. Adventure Contact: Marshal Jon (estarrion).