It is located in a basement of a burned out house northeast of the Spring Mt. Ranch State Park, at the south entrance to Red Rock Canyon. The armory is accessed through a pale yellow cellar door outside of the house.
It is occupied by an unnamed Great Khan and the Great Khan armorer. She will let you trade with her if you have enough fame with the Great Khans.
The armory storage area is to the left, with a workbench and reloading bench to the right. A steel gate protects the armory's merchandise from theft.