I dont see point of adding there Centaurs and Floaters - you can outrun them in real time like any rats etc so they will make no diffrence in encountering anything. But Deathclaws are natural monsters living there I think.
How about Master's army remnants, then?
It's only about nasty long way there over rough terrain and for people with bad Outdoor to stumble every 2 meters in the middle of centaurs. Ah, and btw: rocky terrain won't be suitable for miner tents, so you will HAVE to venture over all the badland. And don't forget delicious irradiated map encounters. The map looks pretty charred down there, i think, for a reason.