Before the Great War, Flagstaff was the first city in a series of carjackings committed by "Shanghai Sally" who was an alleged Chinese spy on the run from law enforcement. In 2255, the ruins of the city were taken over by Caesar's Legion, who christened it as their new capital.
Behind the scenes
- Shanghai Sally: Chapter Closed
- Fallout: New Vegas Official Game Guide Collector's Edition p. 461: "Important Dates
"2248-2274 Caesar conquers the tribes of southeastern Utah, southwestern Colorado, the western edge of New Mexico, and the northern half of Arizona. By 2250 he has declared himself the Son of Mars. By 2255, he has established a capital of sorts amid the ruins of Flagstaff."
(Behind the Bright Lights & Big City)