From A Wiki of Ice and Fire
and the location of the Red Mountains
The Red Mountains or red mountains is a mountain range extending over much of southern Westeros. The mountain range divides Dorne in the south from the Stormlands and the Reach to the north.
Castles in the Dornish Red Mountains include Blackmont, High Hermitage, Kingsgrave, Skyreach, Starfall, Wyl, and Yronwood. The Dornish mountains also contain the ruins of the Tower of Joy and Vulture's Roost. There are two principal passes through the mountains, the Prince's Pass, guarded by House Fowler, and the Boneway, guarded by House Yronwood. The river Wyl flows from the eastern mountains to the Sea of Dorne. The Dornish who live in the Red Mountains are known as stony Dornishmen.
North and northeast of Dorne, the Red Mountains extend along the southern Stormlands to Cape Wrath and almost to Storm's End. This includes the southern Dornish Marches and the marcher castles of Blackhaven and Stonehelm. The vicinity of Stonehelm is known as the Red Watch.
Northwest of Dorne, the mountain range extends into the southwestern Reach. Horn Hill is located in the foothills of the northwestern Red Mountains.