The topic was discussed on the Wizards Boards a few months ago. There were several mentions of the Yehminal (spelling) mountain or mountain range, somewhere between Faerun and Kara-Tur.
The Yehimal mountain range is sort of the dividing point between Kara-Tur, Zakhara and Faerūn.
It is where dwarves first came from, I believe, and from there they settled all three continents (or "land masses" if Zakhara doesn't count as a continent.)