AT APRX 2015 PDT ON 6/13/82, THE ACFT DEPARTED PETALUMA, CA ON A NGT, VFR, X-COUNTRY FLT TO RIVERTON, WY. AN EN ROUTE STOP WAS PLANNED FOR ELCO, NV. NO RECORDS WERE FND OF A WX BRIEFING OR FLT PLAN. THE ACFT WAS DECLARED OVERDUE ON 6/16/82 & THE WRECKAGE WAS FND ON 6/22/82 ON A MTN RIDGE AT AN ELEV OF APRX 7500 FT. AN INVESTIGATION REVEALED THE ACFT HAD IMPACTED IN A STEEP NOSE DOWN ATTITUDE. THE WRECKAGE WAS DISBURSED OVR A SMALL AREA SURROUNDING THE IMPACT PT. THE FUSELAGE, ENG & WINGS WERE DESTROYED BY IMPACT, BUT THE EMPENNAGE REMAINED INTACT. THE TIPS OF THE PROP WERE SHATTERED & CHORDWISE SCORING & LEADING EDGE GOUGES WERE FND ON THE BLADES. THE ESTIMATED TIME OF IMPACT WAS AT 2128 PDT ON A DARK NGT. NO SIGNIFICANT WX CONDS WERE RPRTD. NO PREIMPACT, MECHANICAL DISCREPANCIES WERE FND. THE PLT'S MEDICAL CERTIFICATE REQUIRED THAT HE WEAR CORRECTIVE LENSES & IT WAS NOT VALID FOR NGT FLT OR FOR FLT BY COLOR SIGNAL CONTROL. TWO PAIRS OF SUNGLASSES (IN CASES) WERE FND IN THE WRECKAGE, BUT NONE WERE FND TO HAVE BEEN WORN BY THE PLT.