In The Book
In Immortal Guardians Takoda, Kovo, Olvan, Conor, Meilin and other Greencloaks travel to these mountains to find a sketch that Kovo drew in charcoal, a fanged jaw shaped doorway, and according to a book Erlan showed them in sercret room in the Greenhaven library that stated in was located in The Petral Mountains. They find a secret abandoned city proving no one lived there for a while, also finding that whoever did didn't want anyone to find this doorway, as the planted a trapped moat to protect it. When they get there they collapse in a corridor because Kovo had broken the door that stabilized the rocks.
Not mapped or spoken of in any other books.