It is known that there was an NCR military camp in Willow Beach. However, some time after the First Battle of Hoover Dam the Battle of Willow Beach took place. As a result the camp was destroyed. This later led NCR to be pushed off of the east side of the river.
Behind the scenes
The real Willow Beach is a resort on the Arizona side of the Colorado River, between Lake Mead and Lake Mojave.
Originally, as seen on the map shown during Chris Avellone's Rezzed 2013 talk, the player would've been able to visit Willow Beach as, now called Camp Willow, as a legion controlled area. However due to time, the area was cut.
↑Fallout: New Vegas Official Game Guide Collector's Edition p.372: "Hoover Dam All of the Main Quest in Act III centers around this location, as do the Main Quests involving the visit of President Aaron Kimball. A stronghold of extreme strategic importance for centuries, this location has seen recent turmoil between major Faction too. A few years before current events, Caesar's Legion rolled in, led by ex-Mormon missionary Joshua Graham, Caesar's Legate. Not considering NCR's army to be a serious threat, Graham exercised somewhat lax control over the Legion. During the Battle of Hoover Dam, NCR Rangers and Sharpshooters from First Recon employed risky tactics against the Legion with the help of the enlisted Troopers, and despite horrific loss of life, Caesar's forces were pushed back, but not routed. The NCR has been holding the dam continuously since, and have fortified positions along the dam and up and down the west side of the Colorado River. Recently, the Legion pushed the NCR off of the east side of the river at the Battle of Willow Beach (which destroyed an NCR military camp) and the Battle of Arizona Spillway. Day to day military operations at the dam are under the command of Colonel Moore. While troopers are active here, there are also a large number of civilian contractors who are trying to keep the dam running. They are of a secondary concern to Moore, who is preparing from for an impending attack by Caesar and a visit by President Kimball."