Four States Commonwealth The Four States Commonwealth was one of the thirteen commonwealths of the pre - War United States of America . Created in 1969 , it was comprised of the former states of , , and . In 2247 , the former state of Arizona served as the birthplace of Caesar ' s Legion , a ruthless organization that quickly rose to dominate the majority of the Four States region . Former Utah . As told by Randall Clark , at the start of the war Salt Lake City suffered thirteen direct nuclear strikes . Clark survived by taking refuge in Zion National Park . He eventually returned to find the city " mostly craters and warped steel girders where the buildings were . " Unable to find the remains of his family , he returned to Zion , a place where many sought shelter in the years following the War . In 2062 , many Mormon congregations came together to purchase places in Vault 70 , a Vault - Tec Vault in Salt Lake City . Vault 70 opened in 2190 and its residents used their three G . E . C . K . s to found the city of New Jerusalem in the ruins of Salt Lake City . Most of the cities in Utah were destroyed in the Great War in 2077 and most of the state ' s current inhabitants are tribals ( including the powerful Hecate of Ouroboros and the Blackfoot tribe ) . Burnham Springs , with its horrible mutants is also located within the former borders of Utah . New Jerusalem ' s prophet and apostles repeatedly voted to remain isolated from outsiders , failed communities , refugees , and tribals . In 2233 , a number of angry tribals , raiders , and disassociated attackers ganged up on New Jerusalem , sacking it and killing most of the inhabitants in the process . The new living prophet , Judah Black , led most of the remnants of the Mormon community north to Ogden , Utah , where they established the settlement of New Canaan . The balance of power in the state is not clear due to conflicting information . Caesar claims to control most of " The Utah , " and both Dead Sea and Vulpes Inculta mention being from there . As both are in their thirties , it is clear that the Legion has maintained a presence there for some time . The extent to which they control the territory is not known , but many tribes throughout the state , such as the White Legs and the Dead Horses , live in the shadow cast by the Legion ' s fearsome reputation . According to Jed Masterson , the northern reaches of Utah are controlled by fierce raider groups like the 80s that straddle the line between tribe and gang . As of 2281 , Zion Canyon remains independent , despite encroachments by tribal agents of the Legion . The Grand Staircase , another pre - War national park , also remains free , and is considered by Daniel as a possible evacuation site for the Sorrows , should Zion fall to the White Legs . Dead Horse Point also remains independent , thanks to the intervention of Joshua Graham by leading the Dead Horses away from the Legion . At some point in the first half of 2281 , New Canaan was destroyed by the White Legs ( aided by Ulysses ) , acting on Caesar ' s orders , in order to punish Joshua Graham , Caesar ' s former Legate . The Mormons scattered to the winds with the White Legs in hot pursuit . At some point before " Fallout : New Vegas " , the Courier visited Utah , as is mentioned in comments regarding the current situation of area with Jed Masterson at the beginning of Honest hearts . Former Arizona . Before the war , Mr . House , RobCo , and Vault - Tec created a PDQ - 88b Securitron Vault under the future location of The Fort . After the war , Arizona was badly fragmented with each town fighting others just to survive . Raul Tejada recalls that it was so bad , you couldn ' t trade with a town two miles down the road without getting attacked by raiders . That changed with the arrival of Caesar ' s Legion , formed near the Grand Canyon by two Followers of the Apocalypse and a Mormon missionary . Edward Sallow , one of the Followers , used his knowledge of tactics , warfare , and history to lead the Blackfoot tribe to victory over their enemies . Between 2246 and 2271 , the Legion grew rapidly , conquering nearly all of Arizona and establishing their capital in the ruins of Flagstaff . The NCR holds very little territory in Arizona in 2281 , limited to Bullhead City and the surrounding area . Former New Mexico . Caesar claims that all of New Mexico belongs to him , this is supported by several of the slaves such as Siri . However , whether the entire state actually belongs to him or only part is not known . The Legion started before their encounters with the NCR turned Caesar ' s attention westward , but have continued until the Courier meets Caesar . Siri claims the Legion overran her town in 2278 . The ghoul settlement known as the Reservation , built on the former site of the , is also located in New Mexico . Former Colorado . In 2281 , the Legion controls the eastern and southern portion of Colorado and captures many of its dogs on the streets of Denver , now known as Dog City . According to Legate Lanius , the conquest of Denver was a Pyrrhic victory , owing to the harsh climate , overtaxed supply lines , and a lack of tribal stock to replenish their slave population . The brutal and costly campaign left a strong impression on Lanius and served to slow the Legion ' s expansion , at least for a time . The Handogs were from here before their assimilation into the Legion . The Midwestern Brotherhood of Steel were also stretched out as far as Colorado , though the state of the Brotherhood ( as hinted in " Fallout 3 " ) and rise to power of the Legion leaves a questionable approach to the current status of their power in the region . Joshua Graham states that he has never heard of Legate Lanius , which suggests that either he was simply unaware of him or that the Legion conquered Colorado between 2278 and 2281 . Appearances . Parts of the former Four States Commonwealth appear in " " and " " and its , " Honest Hearts " . Most of the places in " Van Buren " and " Fallout d20 " were located there as well . Parts are also mentioned in " Fallout : New Vegas " and its add - on " Lonesome Road " .