THE ACFT COLLIDED WITH RISING TERRAIN ABOUT 1800 FT BELOW THE CREST OF A RIDGE WHILE ON A PERSONAL FLT IN WX WHICH HAD MULTIPLE CLOUD LAYERS OBSURING THE MOUNTAINS. A CAP ACFT ON A SEARCH MISSION IN THE SAME AREA AT THE APRX TIME REPORTED MULTIPLE CLOUD LAYERS BETWEEN MEDFORD & SUNRIVER, OR. BOTH PLS INVOLVED IN THE ACCIDENT WERE CAP MEMBERS & HAD BEEN ON SEARCH MISSIONS IN THE AREA OF MEDFORD & SUNRIVER ON PREVIOUS FLTS. THE AREA OF THE CRASH IS HEAVILY WOODED WITHTREES OVER 150 FT HIGH. A 4 FT SECTION OF THE LEFT WING WAS FOUND NEAR A FOREST SERVICE ROAD. THE MAIN WRECKAGE WAS APRX900 FT AWAY ON A 180 DEGREE BEARING (MAG), AT THE 3750 FT LEVEL OF A 5580 FT MOUNTAIN. NO FLT PLAN WAS FILED & NO RECORD OF A WX BRIEFING WAS FOUND. THE ACFT DEPARTED DURING A SNOW SHOWER WITH 4 PERSONS ON BOARD; WHEN IT FAILED TO ARRIVE AT MEDFORD A SEARCH WAS INITIATED. THE SEARCH WAS SUSPENDED WHEN NO FLT SIGNALS WERE RECEIVED. SIX DAYS LATER A HUNTER CAME UPON THE WRECKAGE. NO MEDICAL OR MECHANICAL REASON FOR THE ACCIDENT WAS FOUND DURING THE INVESTIGATION.