The Mountains of Sinjian are a treacherous mountain range located along (or at least near) the northern shore of the southern continent, presumably bordering the Sea of Torments. They are far to the east of Beryl, the most ancient of the Jewel Cities. The mountains and their "savage defiles" are mentioned just once, in The Silver Spike.
The Mountains of Sinjian are the eleventh specified location in the long, overland odyssey traveled by the demon called Toadkiller Dog, who was following the trail of his new enemy, the Limper. Toadkiller Dog passed through the mountains only after swimming the River Bigotes and the Hyclades, and traversing the Rani Poor desert, the lifeless landscapes of Barbara, Laba Larada, Khun, the Canyons of the Undead, the ruins of the temple city of Marsha the Devastator, the populated province of Karsus, and the Plain of Dano-Patha. In the mountains, the demon hound found evidence that the Limper had been tormented and delayed with vicious traps left behind by the Lady's Imperial successors. Toadkiller Dog then crossed the Straits of Angine and entered the northern continent, headed toward the Tower at Charm.