BEFORE FLYING, THE PLT TOLD THE FBO THAT HE WOULD STAY IN THE LOCAL REDLANDS/RIVERSIDE, CA AREA. HOWEVER, AFTER TAKING OFF, HE FLEW TO LAS VEGAS, NV. HE DEPARTED LAS VEGAS AT 1636 PDT. WHEN HE DID NOT RETURN TO REDLANDS, A SEARCH WAS INITIATED. THE WRECKAGE OF THE ACFT WAS FOUND ABOUT 8 MI NORTH OF REDLANDS IN MOUNTAINOUS TERRAIN WHERE THE PLANE HAD CRASHED AT AN ELEVATION OF ABOUT 5300 FT. IMPACT OCCURRED AT THE BASE OF A CLIFF IN A CANYON AREA. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FOUND. RADAR INFO INDICATED THE ACFT WAS FLYING AT A SLOW SPEED JUST PRIOR TO THE ACCIDENT. THE IMPACT SITE WAS LOCATED ABOUT 2 MI NORTH OF THE LAST RECORDED RADAR POSITION. A WX STUDY SHOWED THAT THE BASES OF THE CLOUDS IN THAT AREA WAS ABOUT 4000 FT MSL & THE CLOUD TOPS WERE NEAR 5000 FT. FLT VISIBILITY IN CLOUDS WAS ZERO MI & MODERATE TURBULENCE WAS PROBABLE BELOW 10,000 FT MSL.