AT 1830, THE PLT RECEIVED A WX BRIEFING FOR A FLT FROM FAIR OAKS TO SAN JOSE, CA WITH A PASSENGER PICKUP STOP AT SACRAMENTO, CA. DURING THE BRIEFING, HE WAS TOLD THAT HE OUGHT TO BE ABLE TO MAKE IT IF HE TRAVELED BELOW 4000 FT MSL & LEFT WITHIN THE NEXT HR. HE FLEW TO SACRAMENTO & AFTER A PASSENGER PICKUP, HE TOOK OFF AT 1956 FOR SAN JOSE. ABOUT 30 MIN LATER, THE ACFT CRASHED, 43 MI WEST SOUTHWEST OF SACRAMENTO, WHILE ON A NORTHEASTLY HEADING AT AN ELEVATION OF 600 FT MSL. THE CRASH SITE WAS LOCATED ON RISING TERRAIN IN FOOT HILLS, APRX 32 MI TO THE RIGHT (WEST) OF A STRAIGHT LINE NAVIGATIONAL ROUTE BETWEEN SACRAMENTO & SAN JOSE. LOCAL RESIDENTS HEARD THE ACFT & SAW A FIRE FROM THE CRASH. THEY REPORTED THAT THE WX WAS POOR WITH LOW CLOUDS, RAIN, GUSTY WINDS & LIGHTNING. AN EXAM OF THE CRASH SITE REVEALED THAT THE ACFT IMPACTED IN A 60 TO 90 DEG RIGHT WING DOWN, SLIGHTLY NOSE LOW, ATTITUDE. NO PREIMPACT,MECHANICAL MALFUNCTION OR FAILURE WAS FOUND.