BFR TAKEOFF, THE PLT WAS BRIEFED ABT LGT TO MOD RIME ICING IN CLDS & PRECIP ABV THE FRZG LVL. THE FRZG LVL WAS FORECAST TO BE AT 7000' TO 9000' IN THE AREA OF PRESCOTT, SLOPING DOWNWARD TO THE NORTH. THE PLT DID NOT FILE A FLT PLAN, BUT DID RCV VFR FLT FLWG AFTER HE WAS EN ROUTE. DRG THE FLT, HE OBTAINED ADNL WX INFO & FINALLY INDICATED HE WOULD PROCEED TO CEDAR CITY. AT ONE POINT, HE ERRED IN RPRTG HIS ALT. LATER, WHEN ASKED BY ATC, HE SAID THE ACFT WAS NOT ACCUMULATING ICE, ALTHOUGH IT WAS A DARK NGT. AT 1962 MST, THE PLT INQUIRED ABT THE DIST TO CEDAR CITY & WAS TOLD IT WAS AT HIS ONE O'CLOCK PSN AT 23 MI. HE ACKNOWLEDGED & THIS WAS HIS LAST KNOWN TRANSMISSION. SHORTLY THEREAFTER, CONTACT WITH THE ACFT WAS LOST & IT COLLIDED WITH TREES ON WOODED TRRN AT AN ELEV OF ABT 8050'. THE WRECKAGE PATH WAS OVR A 900' AREA. NO PRE-IMPACT MECH PRBLM WAS FND. THE 1950 MST WX AT CEDAR CITY (ELEV 5622') WAS IN PART 1500' SCT, 3000' OVC, VIS 10 MI; BUT IMC WAS RPRTD ABT 15 MI SOUTH. ACFT WAS NOT CERT FOR IFR. PLT RCVD IFR RATING 3 MONS EARLIER; HAD 4.7 HRS ACTUAL WX TIME