Little is known about the location. However, some time after the First Battle of Hoover Dam, the Battle of Arizona Spillway took place here. It later led to the NCR being pushed off of the east side of the river.
The location of the Arizona Spillway is unknown, however the eastern side of Hoover Dam and its spillway being located in what was Arizona, would suggest the battle may have been fought there.
Arizona Spillway is mentioned-only in Fallout: New Vegas.