The Byeshk Mountains are the mountain range that forms the border between Droaam and the Eldeen Reaches. It is largely the home of the Harpy Flights, and has been since longer before the formation of the Kingdom of Galifar. The mountain range gets its name from the plentiful sources of Byeshk that can be found there, which the Dhakaani mined during the Xoriat Incursion to make weapons to fight the Daelkyr. The remnants of these mines can still be found today, and many of them have been taken over by the people of Droaam, who continue to trade byeshk with the druids of the Reaches.
Those mines that haven't been cleared out by the Droaamites are often full of aberrations leftover from the invasion all those years ago.