Iron Mountain

 is an area mentioned by the PoseidoNet terminal in Gecko's reactor #5. It is at least a portion of Enclave Main Comm., and is listed as "operational" by 2242.

Appearances
Iron Mountain is mentioned in Fallout 2, but does not actually appear in any game.

Behind the scenes
There are several such Iron Mountains in the United States; one is a short 9 mile walk to the northwest of Redding, fairly close to Arroyo and Navarro. Another Iron Mountain, located in Utah, is a part of NORAD along with the Cheyenne Mountain Range. However, it is most likely that the location is a reference to the Report from Iron Mountain satirical book.