His father had become violent while trying, without success, to warn Milton and the townsfolk that the town's namesake ridge would soon collapse due to heavy mining and insect tunneling.
After withdrawing from the race he and his uncle drive back to Duane's house from Ridgeburg's ridge.
The camera pans down underground, showing an insect removing a rock from a tunnel under the ridge.
This triggers a landslide, leading to the implosion of the ridge, which Duane and his uncle see from the back of their truck.
The next morning, prior to the election results being announced, it is revealed Mayor Milton has had a heart attack after seeing the ridge collapse, presumably since she realized that Duane's father was right all along.