The miners can be found in the skull of the dead Titan at Titan's Rest (5447, 5030). The stash spawns next to one of the miners every 30 minutes. After looting the stash you will be attacked by all 3 of them and will gain the title "The Red Handed" as a suffix. You do not have to kill the miners to gain the achievement and title.
You can loot the bag more than once for the rewards inside, each time will aggro the friendly nearby mobs.