Describe Balancing Rock and how it was made to balance. What would happen if the rock is dislodged?

Balancing Rock is a rock that is balanced on a cliff at the entrance of Surprise Valley. It was carved by ancient cliff dwellers and, if dislodged, would close the entrance to Deception Pass, locking in the inhabitants of Surprise Valley forever. It can protect Venters and Bess if they are ever attacked as it would kill anyone in its rolling path, but both parties would lose. This is foreshadows an event where someone will be followed to Surprise Valley and try to attack, and the rock will be freed from its perch.