The rock that makes up Camlough Mountain is called granodiorite. Granodiorite, just like the rocks that make up Slieve Gullion, forms from the cooling, deep underground, of molten magma. However, unlike the rocks that make up Slieve Gullion and the Ring of Gullion, which were formed around 60 million years ago, the granodiorites of Camlough Mountain are around 400 million years old. Whereas the younger rocks of Gullion are associated with igneous activity related to the formation of the present day Atlantic Ocean, the rocks of Camlough Mountain are associated with igneous activity related to the closure of a precursor to the present day Atlantic, the now long disappeared Lapetus Ocean.