There's a lot to do here; speak to Rick Baychowski, find the RV and get through the wall of radiation.
How to find Damonta
Ask Around the Prison about Damonta
Visit the Prison on your maps and head along the road until you find Fred. Help him move his wagon using Brute Force and then trade anything you can with him. Ask him about Damonta and he'll tell you about Red.
Head towards the freeway signs and into town. Speak to the trader, Cyril, then head to the gas station with a flag hanging off it. After the cutscene keep moving forward until you get into a conversation with Chris Van Overbake. He demands you pay a weapon tax, so choose the no conversation tree and kill him and his Red Skorpion buddies.
Loot the bodies and go up the path past the beggar. Go up the left path to a gate with two turrets. Destory them and unlock the fence - you'll find Red inside.
He tells you that you need to get through the radiation wall but to do so you'll need rad suits. You'll need to get the rad suits from Rick Baychowski who's been imprisoned at the Ranger Citadel. Time to head back there...
Talk to Rick Baychowski about Rad Suits
Go around the locked elevator in the central area of the Ranger Citadel to the center door. go through and turn right, pass by a Ranger standing guard and through the doors behind him. Down the hall way and around the corner you'll reach the brig. Talk to the jailor who will wake up Baychowski.
Offer to free him and he says he'll lead you to the RV where the suits at stashed. Tell the jailor you need Baychowski for an investigation and he releases him into your custody.
Find Rick’s RV
Get out of the Citadel, open the World Map and then open your Party.
Travel to the X that marks Rick's RV, but get some water from a nearby Oasis if you need it. Rick will take you to the RV (don't let him leave despite him giving you directions), follow the path and take down the enemies.
There's a safe in front of the RV - the combination you get from Rick is 733. Take the Rad suits and go back to the Citadel and send Rick back to the jailor and his cell.
Getting past the Radiation Wall
Damonta is in the far east of Arizona. Equip the Rad Suits and go back to the Prison via the World Map. Travel north and into the radiation area. Head northeast until you get to Titan's Canyon on the map. You're going to have to make your way through this place to get to Damonta.