Cheyenne Mountain, located a fairly short distance outside of Colorado Springs, Colorado, is the home of several branches of the United States military.
History
It has long been public knowledge that Cheyenne Mountain is the home of NORAD, a joint American/Canadian organization devoted to maintaining the security of North American airspace. It's historic task was as watchman for the threat of nuclear attack from the Soviet Union. Unbeknownst to the public, however, Cheyenne Mountain has for the past decade also been home to Stargate Command.
Cheynne Mountain contain's nearly a skyscraper's worth of floors, but with one significant difference to a skyscraper; instead of going 20 or more floors up, it instead descends an unkown number of levels under the mountain. While the full extent of the facilities available to personnel within Cheyenne Mountain is unknown, it is at least certain that the complex sports several cafeterias and troop's barracks, at least one gym, a fully equiped infirmary, and several multi-purpose observation rooms, which are used for such things as complex surgery, interogation, imprisonment, and volatile scientific experiments.
Cheyenne Mountain also appears to include several old missile silos, one of which now houses the Stargate. It is through the surface opening of the gateroom silo that the Stargate was originally moved into the facility sometime prior to the first mission to Abydos.
Alternate realities
The Cheyenne Mountain entrance
- In an alternate reality Cheyenne Mountain was the headquarters of the SGA, a program headed by Catherine Langford that discovered how to activate the Stargate. However, they made an enemy of the Goa'uld. In 1998, Apophis begun to systematically wipe out the Earth. Arguably futile efforts to combat him were headed through the mountain, which Apophis' forces eventually invaded. As many people as possible tried to escape through the Stargate to the Beta Site as possible before his forces captured the entire mountain. To prevent the facility from failing to Apophis' hands, George Hammond ordered Samantha Carter to set the mountain on auto-destruct. The mountain was destroyed just as Teal'c reached the gate room and the Daniel Jackson of our reality escaped. (SG1: "There But for the Grace of God")
- In an alternate reality Cheyenne Mountain was invaded by Apophis' forces led by Teal'c. It was retaken with the help of the Asgard after they were contacted by Dr. Samantha Carter. (SG1: "Point of View")
Behind the scenes
In the real-world Cheyenne Mountain complex, there is actually a security door with blacked out windows labeled "Stargate Command". Behind it is a broom cupboard. (SG1: "True Science")