When arriving at the Nomad camp, the Brakeman will invite you to visit him in his caboose. Do so, and agree to take the Visa card to Head Crusher. Now, get to Quartz and then Scott's Bar in the south. Your man is sitting alone in the southern part of the bar - disband a character and sit with him, then use the Visa card on the chair (or yourself if you're sitting on it).
He will reveal a password to you (Caterpillar). You can then return to the camp, tell the password to the guard at the Atchison tent and then go dig up your reward.
Impatient? Okay. The reward is, from the west end of the southern rail, and twelve steps south. Use a shovel, get your loot and... meet some rail thieves trying to ambush you. Have fun!