Fire Titan

Dwarven legend tells of an ancient and powerful being that crawls deep beneath the surface. Deeper than any tunnel or mine or well, deeper even than the storied "underdark". This entity has risen up twice before, long ago, with wrath so hot it melts rocks and turns metal into gemstone. All that remains of those two eruptions are the Western and Eastern Mountain Ranges.
There are different accounts of what causes it to rise and what causes it to descend back into the depths, but all agree - if it were to return again, it could cause the end of all the peoples on the continent.

Historical Basis

Certainly the mountains exist, but they originated long, long ago. It is also factually true that the western mountain range pre-dates the eastern range. Is there any way to truly verify such an ancient story?

Spread

This legend is mostly told among the Dwarves who make their storngholds in the Eastern Mountains. The Elves do have mention of it amongst their records and written histories, but it's not so interesting to them. Denizens of the Underdark keep away from the area deep beneath the eastern coast, with a concern for the strangely high temperatures there.

Variations & Mutation

Depending on which stronghold you take your story from, there can be considerable variation on what wakes the Titan and what returns it to sleep.
In one, it has been awoken each time by dwarves who were digging alone, away from their clan. They accidentally dug into it. It can only be sent back below by calling on the clan to sing together, using traditional lullabies to send it to sleep.
In another stronghold, it was awoken when a careless dwarf sold an ancient heirloom which was actually a warding anchor holding the beast. To stop the destruction, dwarven adventurers had to find the heirloom and reclaim it.

Cultural Reception

For the Dwarves, the tale has a number of different ideas that it teaches.
It presents an ideal of extreme strength (a creature with the power to make the mountains we call home - now that's impressive!).
It gives their home (the mountain) an interesting and significant history.
It warns against socially unacceptable behaviour and promotes social virtues (in whatever the story teller identifies wakes the beast and sends it back to sleep).