PRIOR TO THE FLT, THE PLT RCVD 2 WX BRIEFINGS & WAS ADZD OF LOW CEILINGS, RESTRICTED VISIBILITIES & MTN OBSCUREMENT ALONG THE ROUTE. ALSO, HE WAS ADZD THAT VFR FLT WAS NOT RECOMMENDED. THE SURVIVING PAX SAID THAT AFTER ENTERING THE MTN AREA, THEY CONTD 'IN AND OUT OF CLOUDS' & THAT THE PLT 'HAD TO CLIMB STRAIGHT UP INTO THE CLOUDS . . . THEN IT (THE ACFT) STRUCK SOMETHING.' THREE HIGHWAY PATROL OFFICERS SAW THE ACFT FLYING JUST BENEATH CLOUDS WHICH THEY ESTD WERE ABOUT 100 FT AGL. THE OFFICERS RPRTD THE ACFT CIRCLED TWICE, THEN PROCEEDED ALONG THE HIGHWAY & DISAPPEARED IN A CLOUD BANK. A SHORT TIME LATER, THE ACFT CRASHED ON STEEPLY RISING, MOUNTAINOUS TERRAIN. INITIAL IMPACT WAS WITH A TREETOP LOCATED IN A RAVINE. BOTH OCCUPANTS WERE WEARING HEAVY SKI CLOTHING. AFTER A TIME, THE REAR SEAT OCCUPANT REGAINED CONSCIOUSNESS & TOOK A BLANKET FROM THE BAGGAGE COMPARTMENT. AFTER SPENDING THE NIGHT ON THE MOUNTAIN SIDE, SHE MADE HER WAY TO THE HIGHWAY FOR HELP.