THE PILOT ATTEMPTED TO EXECUTE A LANDING TO RUNWAY 21 AT THE AIRPORT. THE AIRPORT MANAGER REPORTED THAT THE LANDING OCCURRED DURING DARKNESS AND THAT THE AIRPORT'S RUNWAY WAS UNLIGHTED. ON SITE EXAMINATION OF TRACKS FROM THE AIRCRAFT INDICATED THAT IT TOUCHED DOWN 1170 FEET SHORT OF AND SLIGHTLY LEFT OF THE RUNWAY AND ROLLED 525 FEET BEFORE COLLIDING WITH A GRAVEL EMBANKMENT AFTER WHICH THE AIRCRAFT NOSED OVER.