Cyrios Mountains

The Cyrios Mountains extend from the Frigid Depths to the Wuyun Gates and separate the Menagerie Coast and the Lushgut Forest from the rest of Wildemount.

Mount Mentiri
Northwest of Kamordah, rising above the surrounding mountains, lies the deep red-orange Mount Mentiri. It is widely believed to be the source of the geothermal activity in the area. Isharnai, the Prism Sage lives in a hut at its base. The swamps surrounding the area are inhabited by vast numbers of husk zombies, the remains of those killed when the Julous Dominion wiped out a sect of worshipers of Desirat, the Twilight Phoenix. The sect had a longstanding belief that Mount Mentiri was either the Phoenix's home, or what it became when eventually laid to rest.

Pallid Grove
The Pallid Grove is a valley on the Menagerie Coast in the northern part of the Cyrios Mountains, isolated from the rest of Wildemount by the peaks. It is the home of the pallid elves.

Vol'antim
The aarakocra civilization of Vol'antim is high in the Cyrios Mountains, inaccessible by foot travel.

Dolithil Mine
The Dolithil Mine, near the city of Gwardan and at the edge of the Cyrios Mountains, is a critical source of several metals for the industry of the Clovis Concord.

Before and during the Calamity
Prior to the Calamity, what is now the Pallid Grove was an untouched woodland on a mountain plateau that was home to a group of Sehanine-worshipping elves who used illusions to protect the grove from outsiders. During the Calamity, Torog and his followers broke the protections on the grove and sunk the plateau on which it rested via burrowing beneath it. The forces of Torog then blighted much of the surrounding forest, and dragged the elves underground to be tortured.

Desirat was the companion and mount of Asmodeus during the wars of the Calamity. She was captured and imprisoned beneath Mount Mentiri by the original pre-Divergence Cerberus Assembly and remains there, giving birth to the geo-thermal activity in the area.

Post-Divergence
Kamordah was built with pale stone mined from Mount Mentiri.

During the time of the Julous Dominion, Uk'otoa's followers helped Desirat to establish a following in the area. A group living there built an entire colony based around this god-like creature, calling it the Twilight Phoenix. They burned effigies to it and believed this was its resting place. Indeed, they nearly dug deep enough to free the phoenix. However, they also made a lot of enemies, and the Julous Dominion itself hunted them down and killed them in their homeland around the base of Mount Mentiri.

The elves of the Pallid Grove were long thought to have all perished during Torog's attack, but around 800 PD, pallid elves began to emerge from their underground home amid the sunken roots.

At some point, Isharnai took up residence at the base of Mount Mentiri. Thoreau Lionett, hoping to win success and the affections of Clara, risked walking through the wilderness to find "the witch in the mountains" about whom he had heard stories when he was growing up. Despite wearing out his shoes and being chased by wolves, in a diminished state he stumbled upon the hag Isharnai, who claimed to specialize in fortunes. The fortuneteller offered him a deal: in exchange for "a fragment of [his] fortune," he would get what he always wanted. He agreed, so she told him to pick a place in the mountains and the ground would grow, that he would be a craftsman of fine spirits, and that "a young beau will take on the great name to continue the success, until everything eventually will humble [him] by that which [he] desired most." He borrowed what he could from Clara's family to buy derelict farm property in the hills on the north side of Kamordah and grew grapes on it, with amazing success.

Chapter 16
Hoping to break the curse that kept Nott in goblin form, the Mighty Nein trekked into the Cyrios Mountains in search of Isharnai, along the way battling harpies and stumbling across acid geysers in a foggy valley. They found Isharnai's hut, and after a series of discussions in which she tried to tempt them into deals, Jester Lavorre managed to trick Isharnai, under magical influence, into breaking the curse. The party then quickly left before the hag could realize what had been done.

Trivia
In the Nine Hells, the underground prison beneath the City of Dis is called the Mentiri. That the underground prison for Asmodeus's mount is called Mount Mentiri is presumably not a mere coincidence.