Flagstaff is mentioned only in the Fallout: New Vegas Official Game Guide.
- 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)