A Cracked Earth
The Cliffwall Crack seems to correspond to most of the mapped region of the southern cliff of of the plateau to the north of Spireview. It is not visible from a distance (looking like the side of the cliff, until approached to within 60 feet, at which point one can see across to a deep desert vista. The crack itself shimmers visibly and seems to respond to harsh weather, growing murkier if their are higher winds on either side.
Water that flows across the crack does not appear on the other side (though water carried in containers by individuals moving across the crack does).