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 Utah, Colorado, Arizona, and New Mexico. 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." According to Jed Masterson, Utah is mostly inhabited by raiders, degenerate tribes, and regional warlords.

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. The extent to which they control the territory is very minor, but many tribes throughout the state, such as the White Legs and the Dead Horses, live in the shadow cast by the Legion or are otherwise in contact with them. 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. Ulysses, acting on Caesar's orders, did so to punish Joshua Graham, Caesar's former legate. The remaining 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 the area with Jed Masterson at the beginning of Honest Hearts.

Former Arizona
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. This 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 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. Mr. House controls a pre-War securitron vault under the weather monitoring station at The Fort.

During the events of Fallout: New Vegas, the Courier is abducted by Elijah and taken to the Sierra Madre located somewhere around the Grand Canyon to break into it so Elijah can exploit its technology.

Former New Mexico
Caesar claims that all of New Mexico belongs to him and this is supported by several of the slaves, such as Siri, who tells the Courier that the Legion overran her town in 2278.

The ghoul settlement known as the Reservation, built on the former site of the Los Alamos National Laboratory, 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, home of the Hangdog tribe before their assimilation into the Legion. 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 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.

Former Utah

 * Burham Springs (Van Buren)
 * Dead Horse Point (Mentioned in Honest Hearts)
 * Fort Abandon (Van Buren, Mentioned in Fallout: New Vegas)
 * Fountain Green (Mentioned in Honest Hearts)
 * Grand Staircase (Mentioned in Honest Hearts)
 * Great Salt Lake (Mentioned in Fallout: New Vegas, Honest Hearts)
 * Nephi (Mentioned in Honest Hearts, Fallout: New Vegas cut content)
 * Ogden (Mentioned in Fallout: New Vegas, Honest Hearts, appeared in Van Buren)
 * New Canaan (Mentioned in Fallout: New Vegas, Honest Hearts, Van Buren)
 * Jericho (Van Buren)
 * Ouroboros (Van Buren)
 * Provo Bay (Mentioned in Honest Hearts)
 * Rockville (Mentioned in Honest Hearts)
 * Salt Lake City (Mentioned in Honest Hearts)
 * New Jerusalem (Mentioned in Van Buren)
 * Spanish Fork (Mentioned in Honest Hearts)
 * Syracuse (Mentioned in Honest Hearts)
 * The School (Mentioned in Honest Hearts)
 * Toquerville (Mentioned in Honest Hearts)
 * Zion Canyon (Honest Hearts)

Former Arizona

 * Arizona Spillway (Mentioned in Fallout: New Vegas)
 * Bloomfield Space Center (Van Buren)
 * Bullhead City (Fallout: New Vegas Official Game Guide)
 * Camp Willow (Mentioned in Fallout: New Vegas)
 * Deathclaw promontory (Fallout: New Vegas)
 * Dry Wells (Lonesome Road)
 * Flagstaff (Mentioned in the Fallout: New Vegas Official Game Guide and Wastelanders)
 * The Fort (Fallout: New Vegas)
 * Grand Canyon (Mentioned in Fallout 2, Fallout: New Vegas, Appeared in Van Buren)
 * Sierra Madre (Mentioned in Fallout: New Vegas, appears in Dead Money)
 * Lakelurk cove (Fallout: New Vegas)
 * Legate's camp (Fallout: New Vegas)
 * Phoenix (Mentioned in Honest Hearts)
 * Tibbets Prison (Van Buren)
 * Two Sun (Mentioned in Fallout: New Vegas)
 * Yuma Proving Ground (Mentioned in Fallout: New Vegas)

Former New Mexico

 * Albuquerque (Mentioned in Wastelanders)
 * The Reservation (Van Buren)

Former Colorado

 * Black Canyon (Mentioned in Van Buren)
 * Boulder Dome (Van Buren)
 * Buena Vista (Fallout Tactics)
 * Denver (Mentioned in Fallout: New Vegas, Lonesome Road, appeared in Van Buren)
 * Maxson bunker (Van Buren)
 * Mesa Verde (Van Buren)
 * Nursery (Van Buren)
 * Rocky Mountain Arsenal (Van Buren)
 * Twin Mothers (Van Buren, mentioned in Lonesome Road)
 * Vault 29 (Van Buren)
 * Cheyenne Mountain:
 * NORAD (Mentioned in Fallout 2)
 * Vault 0 (Fallout Tactics)

Appearances
Parts of the former Four States Commonwealth appear in Fallout Tactics and Fallout: New Vegas and its add-on 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, as well as the Fallout 76 update Wastelanders.