THE PLT HAD ORIGINALLY REQUESTED A WX BRIEFING AT 0444 FOR A FLT FROM CHEYENNE,WY TO LOVERLOCK,NV. PRIOR TO DEPARTING CHEYENNE AT 0630, THE FBO TOLD THE PLT THAT THE LOVELOCK ARPT WAS FLOODED. THE PLT REPLIED HE WOULD LAND AT A STRIP IN TOWN. FUEL RECEIPTS SHOWED THE ACFT WAS REFUELED ON 5/4/84 AT RAWLINGS, WY; EVANSTON, WY; WENDOVER, UT; & WINNEMUCCA, NV. AT ABOUT 2030, THE OWNER OF THE PRIVATE STRIP HEARD THE ACFT FLY OVER & TURNED ON A RED BEACON ATOP HIS RESIDENCE. HE OBSERVED THE ACFT PASS OVER THE STRIP AT ABOUT 200 FT AGL, PROCEEDING EAST, WITH SOUNDS OF REDUCED POWER. HE SAW THE LIGHTS OF THE ACFT INITIATE AN APPARENT LEFT TURN, THEN PLUNGE TO THE GROUND. THE ACFT IMPACTED IN A STEEP DESCENT. NO PREIMPACT, MECHANICAL MALFUNCTION OR FAILURE WAS FOUND. A TOXICOLOGICAL TEST OF THE PLT'S BLOOD REVEALED ONLY A LOW LEVEL OF CARBON MONOXIDE (8%). A WITNESS ESTIMATED THAT THE WIND WAS FROM 250 DEG AT 15 GUSTING 20 KTS. THE ACFT HAD LANDED AT THIS STRIP SEVERAL WEEKS PRIOR TO THE ACCIDENT.