In the south, it was an east-west range that divided Dor-Lomin and Mithrim to the north from Beleriand to the south, then in the east it curved around to the northwest, forming the boundary of Hithlum. A line of hills to the southwest formed the southern boundary of Nevrast, while the Mountains of Mithrim were a northwesterly spur that separated Dor-Lomin from Mithrim.
Several rivers arose in the Ered Wethrin, including Narog, Teiglin, and Sirion. The easternmost point of the Ered Wethrin reached nearly to the Echoriath, forming a steep-sided valley through which the upper Sirion ran.
The Ered Wethrin disappeared beneath the waves at the end of the First Age.