This mountain chain was once vast and impenetrable, but had the misfortune to named in the binding spell of a mighty demonic(godly?) being, namely that when the Great Mountains are forgotten, then shall it be free.
The cultists of said demon tried vainly to force all intelligent beings out. Because of the stone, gold and other riches it was found impossible and another route was taken…
Now, thousand years later, the Great Mountains are little more than few hills and vast pasture lands, the cult begins to intensify its illegal activities. Even mountains as they were, could not stand in the way of intensive mining, and covert disintegrating of stone (all magic-users of the cult are now masters of the spell). The cult, rich of all the mining, is slowly redirecting its attention to other things needed to make everybody forget this mountains:
- claiming all locations not yet mined
- finding all resources of information even incidentally mentioning the Great Mountains (already having gigantic archives on this) and slowly disposing of all of them - this means people, too
- promote a new name for this area and make everyone forget the old one
- remove obstacle for mining company, like a monster or whatever (Yes, you may well begin your adventure-career working for the Enemy :-)
- get somehow a book/scroll/map/tapissery/ceramics/... for a “wealthy collector”
- items (mentioning the Mountains) were stolen, get them back, including the worthless ones
- some magical thingy cannot be destroyed and/or moved (mysterious obelisks with map etc.), the heroes are tricked into believing its cursed/evil and must destroy it somehow
- unimportant poor people get harrased/robbed for no apparent reason
- a freak-show has the so-called Last Stone of the Great Mountains, protect them from attacks or steal it
Heroes can naturally be cultists themselves - maybe only a few of them, secretly (evil grin) - working for the Great Freeing ... for any party - good,evil,whatever . It is possible to begin in the cult, then discover the being/god you try to free is actually the wrong alignement.