THE FLIGHT ORIGINATED AT RENO, NV, BUT THE PILOT LANDED AT RED BLUFF, CA AFTER RECEIVING AN IN-FLIGHT WEATHER BRIEFING. AFTER LANDING, HE OBTAINED ANOTHER WEATHER BRIEFING AND WAS ADVISED THAT VFR FLIGHT WAS NOT RECOMMENDED. HE THEN FILED A VFR FLIGHT PLAN AFTER REPORTING THAT THE PASSENGERS WERE ANXIOUS TO GET HOME, OTHERWISE HE WOULD STAY. THE FLIGHT PLAN WAS FILED FOR 8500 FT. THERE WERE NO KNOWN COMMUNICATIONS WITH THE AIRCRAFT AFTER THE PILOT ACTIVATED HIS FLIGHT PLAN. THE PLANE COLLIDED WITH TREES AND CRASHED ON DOWNSLOPING TERRAIN ABOUT 12 MI NORTHEAST OF MT SHASTA. THE IMPACT OCCURRED ON A SOUTHERLY HEADING AT ABOUT 7000 FT MSL. ACCORDING TO A WEATHER STUDY, THERE WOULD HAVE BEEN EXTENSIVE CLOUDS BETWEEN 5500 AND 10,000 FT WITH SCATTERED RAIN SHOWERS. ALSO, THERE WOULD HAVE BEEN MIXED RIME AND CLEAR ICING IN CLOUDS AND RAIN SHOWERS ABOVE APPROXIMATELY 6300 FT AND TURBULENCE WAS FORECASTED BELOW 18,000 FT.