Area 51

Area 51 was a military base in Nevada, and a former testing ground for experimental government aircraft and extraterrestrial phenomena.

Background
Area 51 housed some alien technology, including a captured flying saucer. This was later retaken by aliens, but then crashed somewhere in California.

Appearances
Area 51 is mentioned in Fallout, as a print on a flying saucer in the Alien Ship special encounter. It was to appear as a location in Fallout 2 and be inhabited by a group of scientists, but was cut from the final version of the game.

Behind the scenes

 * In one of the first versions of Fallout 2, Lynette's talking head was supposed to be used for a spokesperson for a group of scientists living in the ruins of Area 51.
 * Area 51 is based off of the real world Groom Lake Facility, code named Area 51. It is located within the Nevada National Security Site. The base is used by the United States military to develop and test many top secret aircraft and weapons technology, though it has long been a source of speculation among conspiracy theorists. Many theories involve captured aliens and their technology, hence why the location is mentioned on a crashed alien ship in Fallout.
 * When asked why the base was not included in Fallout: New Vegas, Joshua Sawyer expressed that the land between New Vegas and Area 51 was not close nor interesting enough for inclusion. In addition, he remarked on the popular culture association between the base and extraterrestrials, which had been covered in the Fallout 3 add-on Mothership Zeta.