THE PLT FILED A COMPANY VFR FLT PLAN & TOOK OFF AT APRX 0930 MDT ON A RETURN FLT TO FARMINGTON, NM. ACCORDING TO A SURVIVING PASSENGER, AFTER DEPARTING BLANDING, THE ACFT ENTERED LOW CLOUDS. REPORTEDLY, THE PLT FLEW IN THE CLOUDS FOR A PERIOD OF TIME UNTIL HE FOUND AN OPEN SPOT, THEN DESCENDED BELOW THE CLOUDS. THE PASSENGER STATED THAT THE PLT CONTINUED THE FLT 'GOING BACK & FORTH, UP & DOWN... CANYONS.' HE STATED THE PLT 'STARTED BACK UP IN THE FOG & I THOUGHT HE KNEW WHERE HE WAS GOING.' HE REPORTED THAT A FEW MINUTES AFTER ENTERING THE FOG, THE ACFT CRASHED. A SEARCH WAS INITIATED AFTER THE ACFT WAS REPORTED OVERDUE. IT WAS FOUND AT APRX 1517 WHERE IT CRASHED & BURNED ON SLEEPING UTE MOUNTAIN AT THE 7800 FT LEVEL. AN EXAM OF THE WRECKAGE REVEALED THE ACFT IMPACTED RISING TERRAIN IN A NOSE HIGH ATTITUDE. NO PREIMPACT, MECHANICAL FAILURE/MALFUNCTION WAS REPORTED. THE PLT WAS INSTRUMENT RATED, BUT WAS CERTIFIED FOR VFR FLT ONLY FOR OPERATIONS UNDER PART 135 OF THE FAR'S.