Then, you can speak to Papa Khan, though he won't have much to say to you. This will ensure that if you haven't learned about a possible Great Khan-Caesar's Legion alliance somewhere else in the game before undertaking this side quest, you'll know now. Speak to everyone, leaving the Great Khan leader, Papa Khan, for last. As long as it's at a reasonable hour, you'll find men and women sitting around eating.
These guys are the key to getting this side quest going. Either way, when you arrive, seek out the longhouse on the compound, where the Great Khan leadership is located. Ranch State Park to the south, or Remnants Bunker and Ranger Station Foxtrot to the north. If you want a good point to spring-off from that's somewhat close by, however, consider Spring Mt. That is to say, you're going to have to go overland through treacherous, mountainous terrain in order to get there. Unfortunately, Red Rock Canyon is one of those few locations on the map that don't have an easy springing-off point.
This side quest is intimately intertwined with the faction known as the Great Khans, who are located in their greatest numbers at their main encampment, Red Rock Canyon on the far western edge of the Mojave Wasteland. This side quest can be, in a word, complicated.