Bitter Gorge (American Post-Civil War Westerns) by William Black

After finding a train schedule in the pocket of a dead outlaw, Sheriff Dean uncovers a most sinister plot of the deadly militia Los Bandidos Rojos. There’s a train car full of gold and the militia is going to send it over the bridge at Bitter Gorge. If that train reaches Bitter Gorge, it’ll leave hundreds dead. Sheriff Dean won’t let that happen.