BEFORE TAKEOFF, THE PLT RECEIVED A WX BRIEFING & WAS ADVISED TO EXPECT IFR CONDITIONS IN THE VICINITY OF OCEANSIDE, CA & THAT MODERATE TURBULENCE EXISTED BELOW 20,000 FT. AFTER TAKEOFF, HE OBTAINED AN IFR CLEARANCE TO CLIMB & CRUISE AT 6000 FT. AT ABOUT 2005 PST, ATC LOST RADIO & RADAR CONTACT WITH THE ACFT. LATER, THE ACFT WAS FOUND WHERE IT HAD CRASHED IN MOUNTAINOUS TERRAIN, ABOUT 1/5 MI FROM WHERE THE LAST TRANSPONDER REPLY WAS NOTED. AN EXAM OF THE WRECKAGE REVEALED BOTH OUTER WING PANELS, THE RIGHT STABILATOR & THE VERTICAL STABILIZER HAD SEPARATED & WERE FOUND 130 TO 612 FT FROM THE MAIN WRECKAGE. ALSO, THE REMAINDER OF THE EMPENNAGE HAD SEPARATE & WAS 31 FT FROM THE MAIN WRECKAGE & THE BOTTOM SECTION OF THE FUSELAGE & ROTATING BEACON WERE 823 FT AWAY. THERE WAS EVIDENCE THE MAIN WRECKAGE HAD IMPACTEDIN A NEAR VERTICAL DESCENT. ALL SEPARATED PARTS HAD EVIDENCE OF OVERLOAD FAILURE. PERSONNEL NEAR THE ACCIDENT SITE REPORTED "SHAFTS OF HEAVY RAIN." AT APRX 2018, A CESSNA 210 PLT RPTD HEAVY RAIN ABOUT 1 MI NORTH OF THE ACCIDENT SITE.