THE PLT HAD DEPARTED MAZATLAN, MEXICO AT 0632 PST & HAD LANDED AT LOS MOCHIS & MEXICALI, MEXICO & AT CALEXICO, CA, WHERE HE CLEARED U.S. CUSTOMS. BEFORE DEPARTING CALEXICO, HE TELEPHONED HIS FAMILY & TOLD THEM THE WX HAD BEEN POOR ALL DAY. THE ESTIMATED TIME OF ARRIVAL AT YUMA, AZ WAS 1730 PST. WHEN THE ACFT DD NOT ARRIVE, A SEARCH WAS BEGUN. THE WRECKAGE WAS FOUND ABOUT 17 MI EAST OF IMPERIAL, CA, WHERE THE PLANE HAD CRASHED ON A WESTERLY HEADING. AT THE TIME OF IMPACT, THE ACFT WAS ESTIMATED TO HAVE BEEN IN A 15 DEG DESCENT & IN A 65 DEG RIGHT BANK. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FOUND. WITNESSES ATTESTED TO WORSENING WX & GUSTY WINDS IN THE VICINITY AT THE PRESUMED TIME OF THE CRASH. THE CO-OWNER NOTED THERE WAS A 600 FT ERROR IN THE ALTIMETER, WHICH THE PLT WOULD COMPENSATE FOR, BY ADJUSTING THE BAROMETER SETTING.