Hoover Dam Hoover Dam , called the Old World Wall by Ulysses , is a concrete arch - gravity dam in the of the Colorado River . It lies on the border between the former US states of Arizona and Nevada . Background . Before the Great War , the Hoover Dam was a main power supplier to the greater Four States Commonwealth ( Arizona and New Mexico ) along with the Southwest Commonwealth ( parts of California and Las Vegas ) and possibly parts of the Texas Commonwealth . When the Great War first broke out , some of Mr . House ' s long and short range missiles systems kept the Hoover Dam in almost untouched condition along with a majority of Las Vegas ; however due to the war the plant was shut down , whether this is from the Great Blackout or not is unknown . In 2274 after a long period of lying dormant , Hoover Dam was taken by the New California Republic with the arrival of the first NCR scouts at Hoover Dam . This action spurred Mr . House into action as a sign of returning civilization . Mr . House then sent his Securitron army out onto the New Vegas Strip and rallied the tribals occupying the city , ensuring that when the NCR first reached New Vegas , they would return with stories of a city of lights in the middle of the desert , bringing in the tourist revenue required for Mr . House to carry forward his plans . He worried about the independence of his new city ' s power source , but fortunately the arrival of Caesar ' s Legion in the region meant that the NCR could not take the Dam and the Strip without significant casualties , which would leave them vulnerable to the Legion . Mr . House and the NCR drew up the New Vegas Treaty , out of necessity more than anything . 95 % of the Dam ' s power output would go to the NCR , and in return Vegas ' independence would be guaranteed . In 2277 , the Legion , led by the Malpais Legate , briefly took the Dam , but were defeated shortly after when the NCR performed a tactical retreat to destroy the Legion by trapping them in Boulder City . After the Battles of Willow Beach and Arizona Spillway , the Dam stands as the only foothold the NCR has east of the Colorado River . It is the central point of the power struggle between NCR , the Legion , and Mr . House , and with the Second Battle of Hoover Dam on the horizon , it is certain that the outcome will determine the fate of the entire Mojave Wasteland . While troopers are active here , there are also a large number of civilian contractors and engineers who are trying to keep the dam running as smoothly as possible . They are of a secondary concern to Moore , who is preparing for an impending attack by Caesar and a visit by President Kimball . Layout . Hoover Dam covers a large area with extensive exterior and interior sections , despite there only being one map marker for the entire location . Following the Colorado River downstream ( or coming upstream from Cottonwood Cove ) , the player will encounter a pontoon barrier presumably to keep the Legion at bay . Exterior . The west side of the dam is controlled by the NCR and features the anti - aircraft gun seen on billboards . The fast - travel map marker puts the player just outside of the entrance to the Hoover Dam visitor center . Just north of the visitor center building is a stage and viewing area . To the west of the stage is a large anti - aircraft cannon . Continuing north along the barricaded road leads to the top of the dam itself . Two towers are along the south edge of the road . Access to Hoover Dam Intake Tower 01 and 02 is via a bridge connected to the north side of the road . The road ends at a checkpoint door which is inaccessible until the final quest , such as Eureka ! The checkpoint contains a Very Hard locked terminal , and a few lockers with minor loot . It also houses a small sniper nest on the roof , accessible via a ladder . Access to the north and south bases of the dam are blocked off by a pontoon barrier when attempting to swim downriver toward it . Pontoons hold sections of chain link fence in place along the top of the water , while weights keep the submerged ends in place and the whole structure taut . While it is possible to get above the top of the chain link fence from the water , invisible barriers prevent you from actually hopping over it , even when attempted from the cliffs far above the barrier ; though it is possible to jump off the north side of the dam into the water . This places the player on the opposite side of the pontoon barrier and allows the player to swim the length of the Hoover Dam . A one - way ladder upwards is available to return to the top of the dam on the NCR side of the river . The east side of the dam is controlled by the Legion . Going west along the barricaded road leads to the top of the dam itself . Access to Hoover Dam Intake Tower 03 and 04 is via a bridge connected to the north side of the road . There are two towers along the south edge of the road , one is ruined . The south base of the dam is accessible by descending through interior sections of the dam and exiting from the second tier of either Hoover Dam Power Plant 02 or 04 . There are spectacular gushers of water from outflow pipes high up on the east and west walls of the river canyon . You can swim from the west to the east side and climb up on the concrete area by swimming all the way to the south end and walking up the sandbar to the southeast corner . Interior . See the individual buildings and sections for descriptions of the dam interior . Appearances . Hoover Dam appears in " " and was going to appear in the canceled " Van Buren " .