THE PLT & HIS DAUGHTER WERE BELIEVED TO HAVE DEPD HIS PVT AIRSTRIP ON 11/22/86 OR 11/23/86. THEY WERE RPRTD MISSING ON 11/24/86 & A SEARCH WAS BEGUN, BUT THE ACFT WAS NOT FND UNTIL 8/19/88, WHEN THE WRECKAGE WAS DISCOVERED BY HUNTERS. THE CRASH SITE WAS LOCATED ABOUT 10 MI NORTH OF THE PLT'S AIRSTRIP. AN EXAM REVEALED THE ACFT WAS TRAVELING ON A NORTH- WESTERLY HEADING WHEN IT STRUCK A TREE NEAR THE TOP OF A RIDGE. THE ACFT THEN CRASHED TO THE GROUND & CAME TO REST AGAINST A TREE ON THE RIDGE. THE ACFT WAS DESTROYED BY IMPACT & FIRE. NO PREIMPACT MECHANICAL MALFUNCTION OR FAILURE WAS FOUND DURING AN EXAM OF THE BADLY BURNED WRECKAGE. THE ACDNT OCCURRED ON HILLY/MOUNTAINOUS TERRAIN AT AN ELEV OF ABOUT 1800'. AT THE APRX DATE OF THE ACDNT, THE WX WAS GENERALLY VFR. ABOUT 9 MI WEST AT UKIAH, CA, THERE WAS EARLY MORNING FOG & CEILINGS OF 2000' TO 3000' ON 11/22/86, WHICH CHANGED TO SCATTERED CLOUDS IN THE AFTERNOON. ON 11/23/86, NO CLD LAYERS WERE RPRTD BEL0W 20,000'. THE PLT WAS RPRTD TO BE DESPONDENT OVR SEPN FM HIS WIFE, 2 WKS BFR THE ACDNT.