THE AIRPLANE COLLIDED WITH NEARLY LEVEL TERRAIN ABOUT 3 MI SE OF THE DESTINATION AIRPORT. THE TERRAIN WAS SNOW COVERED, FEATURELESS, UNILLUMINATED, AND THE NIGHT SKY WAS VERY DARK. THE AIRPORT IS NOT SERVED BY ANY NAVIGATION AIDS. NAVIGATION IN THE AREA IS DONE BY 'PILOTAGE.' WITNESS REPORTS INDICATED THE VISIBILITY OF GROUND REFERENCE OBJECTS WAS NOT POSSIBLE DUE TO THE TOTAL DARKNESS AND LACK OF CONTRAST WITH COMPLETE SNOW COVERED TERRAIN. THE ACCIDENT OCCURRED PRIOR TO THE ONSET OF CIVIL TWILIGHT. NO RECORD OF PRE-DAWN COMPANY FLIGHTS BY THE PILOT DURING THE PAST 90 DAYS WERE FOUND. CESSNA AIRCRAFT COMPANY PROVIDES A WARNING 'FEATURELESS TERRAIN ILLUSION, AN ABSENCE OF GROUND FEATURES, AS WHEN LANDING OVER WATER, DARKENED AREAS AND TERRAIN MADE 'FEATURELESS BY SNOW' CAN CREATE THE ILLUSION THAT THE AIRPLANE IS AT A HIGHER ALTITUDE THAN IT ACTUALLY IS. THE PILOT WHO DOES NOT RECOGNIZE THIS ILLUSION WILL TEND TO FLY A LOWER APPROACH.'