The Lost Art
Formed as a last line of defense against Infernal invasions that threatened all of the continent. The Rift is not merely a valley, it is a planar boundary. In truth, the Prime is divided into two sub-planes. This division can easily be crossed physically, though, leading to odd relationships with Magic. It runs the entire length of the Plane, north to south, and simply cuts through all physical features. It extends endlessly in both directions vertically, with the farthest reaches adjoining the Astral Plane in a coterminous-like fashion.
The Rift is exactly 66ft across.