Following the destruction of the Alpha Site by Anubis, P4X-650 was chosen as the new location for the SGC's off-world base. The world of forests and mountains is 640 light years from Earth, and the Alpha Site facility was built inside a mountain, much like the SGC. The base is large enough to house several F-302s in a hangar within the mountain, and it provides a secure sanctuary and base of operations for off-world SG teams. Colonel Pierce has served as commander of the Alpha Site on P4X-650.
Cross Reference: Alpha Site, Colonel Pierce, Captain Shefield
Episode Reference: Covenant, Endgame, Gemini