THE PLT & PAX INTENDED TO LOOK OVR PROPERTY & LOOK FOR MOOSE. THE PLT RPRTD THEY FLEW UP & DOWN SVRL CANYONS AT ALTS BTN8000 & 10,000 FT MSL. SHORTLY AFTER ENTERING A 45 DEG BANK TURN FOR A 2ND PASS OVER AN AREA, THE PLT HEARD A 'MUFFLED POP' THAT HE BELIEVED HAD COME FROM THE FWD PART OF THE ACFT. HE SAID HE NOTED A FLUCTUATION OF THE MANIFOLD PRESSURE & BELIEVED HE HAD AN ENG PRBLM. AT ABOUT THAT TIME, THE ACFT HIT TREES & CRASHED ON SNOW COVERED TERRAIN. DENSITY ALTITUDEWAS APRX 11,000 FT. THE REAR SEAT PASSENGER (WITH ONLY MINOR INJURIES) WALKED 6 MI FOR HELP. AN INVESTIGATION REVEALED THE INITIAL IMPACT OCCURRED WHEN THE RIGHT HORIZONTAL STABILIZER HIT A TREE AT APRX 35 FT AGL & 460 FT FROM THE FINAL RESTING PLACE. THE ACFT THEN FLEW APRX 300 FT, WHERE THE LEFT WING TIP HIT A 2ND TREE. BEYOND THE 2ND TREE, THE PROP HAD SEVERED NUMEROUS TREE BRANCHES. THE REAR SEAT PASSENGER STATED THE ACFT WAS CIRCLING AT LOW ALT; SHE DIDN'T HEAR ANY CHANGE IN ENG SOUND, BUT HEARD THE STALL WARNING JUST BFR CRASHING. NO PREIMPACT PART FAILURE/MALFUNCTION WAS FND.