A non-verbal teenager's affinity for rocks has proved to be life-saving after the sound of him banging them together alerted a rescue team to his location.
The teen ran into nearby trees and went missing after going on a hike with mother and sister in Los Angeles, California.
Members of the search and rescue team said they heard a "piercing sound" through the thick bushes of the Crescenta Valley Park, where they were searching for the developmentally-delayed teen.
