Four States Commonwealth

The  was one of the thirteen commonwealths of the pre-War United States of America. Created in the mid 21st century, 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.

Utah

 * Dead Horse Point (Honest Hearts)
 * Fountain Green (Honest Hearts)
 * Grand Staircase (Honest Hearts)
 * Great Salt Lake (Fallout: New Vegas, Honest Hearts)
 * Nephi (Honest Hearts)
 * New Canaan (Fallout: New Vegas, Van Buren)
 * Ogden (Fallout: New Vegas, Van Buren)
 * Ouroboros (Van Buren)
 * Provo Bay (Honest Hearts)
 * Rockville (Honest Hearts)
 * Salt Lake City (Honest Hearts)
 * Spanish Fork (Honest Hearts)
 * Syracuse (Honest Hearts)
 * Toquerville (Honest Hearts)
 * Zion Canyon (Honest Hearts)

Arizona

 * Bloomfield Space Center (Van Buren)
 * Bullhead City (Fallout: New Vegas Official Game Guide)
 * Flagstaff (Fallout: New Vegas Official Game Guide)
 * The Fort (Fallout: New Vegas)
 * Grand Canyon (Fallout: New Vegas, Van Buren)
 * Phoenix (Honest Hearts)
 * Tibbets Prison (Van Buren)
 * Two Sun (Fallout: New Vegas)

New Mexico

 * The Reservation (Van Buren)

Colorado

 * Boulder Dome (Van Buren)
 * Buena Vista (Fallout Tactics)
 * Denver (Fallout: New Vegas, Van Buren)
 * Maxson Bunker (Van Buren)
 * Mesa Verde (Van Buren)
 * The Nursery (Van Buren)
 * Twin Mothers (Van Buren)
 * Vault 0 (Fallout Tactics)
 * Vault 29 (Van Buren)

Utah Wasteland
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 use 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 Ouroborus and the Blackfoot tribe). Burnham Springs, with its horrible mutants is also located within the former borders of Utah.

New Jerusalem's intolerant 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. 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

Arizona Wasteland
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.

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 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.

New Mexico Wasteland
The New Mexico Wasteland also belongs, partially, to the Legion. They had conquered the western half of the former state before encounters with the NCR turned Caesar's attention westward.

The ghoul settlement known as the Reservation, built on the former site of the Los Alamos National Laboratory, is also located in New Mexico.

Colorado
In 2281, the Legion controls the 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.

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.