The High Plateau was a region of bad lands that would have been found north of Danjirland and south of the Seolfar Strake (Seoltang: "Journey To Strike Silver") in the Kelfour's Landing region. It was the source of the high quality granite used to construct The Graveyard of the Etrevion family, and was the location of the ruined city of Quellburn (Seoltang: "Freezing Creek") in the I.C.E. Age history. (The citadel was straight north from the volcano Blototh (Seoltang: "Blown/Windy Mountain").) It marked the windward edge of the so-called "West Country", the "land of the dead" that had been the fiefdom of Kestrel Etrevion. In principle the region was controlled by Lorgalis the White up until his defeat by Jaysek (Jastev) at the end of the Wars of Dominion.
In the middle of the Wars of Dominion or perhaps near the end, most likely after the conquest of Saralis and the absorption of The Dark Path into the dominion of Lorgalis, there was a group of refugees fleeing the Cult of the Desert Dog from Zor which was west of the Grey Mountains. The kingdom of Zor had long since been annihilated by this cult of the Unlife, where these refugees would have been fleeing from what we call dark assassins. When they stumbled upon the cliffs of the Colewaether River (Seoltang: "Freezing Water"), they followed it until reaching its dead end at Claedesbrim Bay (Seoltang: "Foggy Edge of Sea").
They were essentially trapped in the open by the cliffs, so they made it appear they had committed mass suicide while hiding in a cavern. Since they had been saved by clerics finding the concealed opening and sacrificing themselves to make the illusion convincing, and the other powerful spell-casters buying them time, they declared the various mages to be their rulers in gratitude for their survival. These people hid out the remainder of the Wars of Dominion, rising presumably in the aftermath of Lorgalis' defeat, thus founding the city of Quellburn to be ruled by one member from each of the twelve Spellguilds of Zor. There was a central Citadel around which a walled city grew over the centuries.
The land of Quellbourne (Seoltang: "Freezing Lands") was prosperous with mining and coastal villages for thousands of years. In the year 5840 Third Era this ended with the betrayal of Zenon, the Lord Sorcerer of the ruling Council of Mages, who had been corrupted to the Unlife by the high priest of the Cult of the Snow Lion. Zenon orchestrated a massive invasion by organizing an alliance with Ice Kral to the far north and hordes of trolls, as well as monsters of his own devising, combined with demonic pacts he had made with the Pales. Unfortunately, he lost his mind in the battle with the reigning Mystic, and now suffers from amnesia in the ruined city.
Refugees who hid in a spider's lair gave sacrifices to a giant spider, coming to worship the spider goddess and founding the Spider Temple. With the immediate south of Quellburn being the Black Forest of Dir, we know that "Danjirland" is where The Iron Wind rules. When the black reaver was released from a box at the tower there, it contained a note that was written by Zenon. Quellburn was the next logical target of those specific orders of the cult after their destruction of Ugus Fost and much of the mannish and Elven population of the Blue Forest. The Gnolls of Hetoth (Seoltang: "Tall Mountain") went largely into hiding after the collapse of civilization.
Behind the Scenes
The ruined city of Quellburn was a quest area in the I.C.E. Age where the sorcerer Zenon wandered with amnesia. It was why there was an "Old Mine Road" near a town that had only existed for two decades. The term was changed to "Elanith", as was the term Quellbourne. When old NPCs refer to "Elanith", such as the phrase "First Elanith Bank", they are actually referring to the Darkstone Bay region and not the continent of Elanith. The "Kingdom of Elanith" and its Citadel was moved south, serving as the backstory for River's Rest. They were both ruled by a council of mages that was destroyed from within, collapsing alongside an invasion of trolls and krolvin. Unlike the I.C.E. Age version, there is no known link with the Council of Light, or servants of the Unlife such as Zenon. The story of the Zor refugees hiding from their military pursuers in that spot is clearly the source of the Wolves Den story in the modern history. The Colossus is found in the badlands north of Danjirland in what would have been the High Plateau in the archaic lore. While it was part of the Vvrael saga which was nominally modern, it may have been an allusion to the Ugus Fost backstory with the Shards.