During the time of Dragons... two of the most powerful, Naagra and Krymlar, battled one another for complete dominance.  They fought many times... neither one ever truly defeated the other.  For hundreds of years they schemed and planned their next attack.  One day they decided that the battle will be to the death, neither allowed to retreat.

On that day, or days because the battle lasted longer than a day, they fought valiantly.  From the depths of the deepest waters... to the outer reaches of the sky.  The world was their battle ground and no one was safe.  As they battled, their tempers flared and with that a bezerk rage consumed them both.  High in the air they grappled... neither one noticing the earth rising towards them.  They plummeted to the ground... the impact was heard for hundreds of miles... it thundered on for minutes.  No one saw or heard from them again.

After a couple centuries an adventuring Bard discovered a large  impression in the very earth, a canyon 17 miles wide and 26 miles long, which he  believed was created by the impact of the two great Dragons.  He named it Thunder Canyon...