The pilot stated that the aircraft was in level flight at 1,300 feet when the engine ceased operating. During the resulting forced landing the aircraft collided with a rock and flipped upside down, incurring substantial damage. An FAA inspector who examined the accident airplane said that fuel was in the aircraft, but it was contaminated with debris when it was transferred to containers during recovery. Postcrash examination of the aircraft did not reveal any preexisting failure or malfunction.