Final answer:
Gwen Anderson found a hole in the wall on the 11th floor, which was actually a secret passageway. It led to a narrow gorge and a balanced rock used for defense by the cliff-dwellers.
Step-by-step explanation:
Gwen Anderson found a hole in the wall on the 11th floor. This hole was actually a secret passageway.
According to the passage given, Venters discovered a narrow gorge leading down on the other side of the wall. At one side of this gorge, there was an enormous rock that had been carefully balanced by the cliff-dwellers for defense. The little stone-men had chipped and chipped away at this boulder until it rested perfectly on a pin-point of its surface. This rock could be dislodged by strong hands, causing an avalanche and blocking the outlet to Deception Pass.
Based on this information, we can determine that the hole in the wall that Gwen Anderson found was used as a secret passageway that led to the narrow gorge and the balanced rock.