A mountain-range of northern Middle-earth
A northern range of Middle-earth, running west to east and forming the likely northern border of the region of Rhovanion. They were long mined by the Dwarves, who were driven from them in the late Third Age by Cold-drakes from the north, and were later colonised by Orcs. 
Mount Gundabad is the chief of Grey Mountains, from there came Durin the Deathless, first Father of the Dwarves. Dwarves returned to the Mountains after the Dragons perished. Also known as Ered Mithrin.