Ered Lithui
From Tolkien Gateway
The Ered Lithui (Sindarin for "Mountains of Ash") spans from the Morannon, where it meets the Ephel Dúath, then runs generally eastward for hundreds of miles, forming an impenetrable northern border of Mordor. The name "Mountains of Ash" suggests that the range is downwind of Mount Doom and collects its ash fallout.
