The Tethryn range rises in northwestern SW Urok, younger and sharper than the worn Pearly Mountains to the south. These peaks still show volcanic origins—black basalt cliffs, hot springs steaming in high valleys, and soil rich enough to support terraced farms where little else would grow. The range runs roughly east-west, creating a natural barrier between the coastal lowlands around Phiona Bay and the interior plateau where the Thyogres River begins its long journey south.
The Tethryns are most famous for what sits atop them: Xi Chin, the Timekeeper city, whose white marble towers are visible from ships in the Gulf of Xoth on clear days. The mountains' height and the clarity of their air make them ideal for astronomical observation—a fact the city's founders recognized millennia ago.
Several rivers originate in the Tethryn heights. The Pteyalune flows north toward Deadwater Bay, its waters growing colder and more lifeless as they approach that cursed shore. The Freolian drains the eastern slopes, flowing southeast toward the Pearly Mountains—it's the main water-road connecting Xi Chin's region to the interior. The Expation River tumbles down the western face toward Phiona Bay, named (locals claim) by exiles from some forgotten conflict who settled its fertile banks.