THE FLIGHT DEPARTED UNDER INSTRUMENT METEOROLOGICAL CONDITIONS, WITH VISIBILITY RESTRICTED TO ONE QUARTER MILE BY FOG. THE CEILING WAS OBSCURED. AFTER DEPARTURE WITNESSES HEARD THE AIRCRAFT MAKE WHAT APPEARED TO BE A LEFT TURN. NEXT THEY HEARD THE ENGINE SOUND INCREASE FOLLOWED BY A LOUD THUD. THE ACFT WAS FOUND WHERE IT HAD IMPACTED AN EMBANKMENT, NEXT TO A ROAD ON RELATIVELY LEVEL TERRAIN, APPROXIMATELY 1/8 MI FROM THE DEPARTURE END OF RWY 25. NO EYEWITNESSES TO THE ACCIDENT COULD BE LOCATED. AN INVESTIGATION REVEALED THAT THE PLT HAD CALLED THE SACRAMENTO FSS BY TELEPHONE. AT 0771, HE OBTAINED AN IFR CLEARANCE WITH A VOID TIME OF 0730. THERE WERE NO FURTHER COMMUNICATIONS BETWEEN THE PLT & THE FSS. BEFORE TAKEOFF, THE ACFT WAS PARKED ABOUT 2 MIN TAXI TIME FROM RWY 25. ACCORDING TO THE FAA INSTRUMENT FLYING HANDBOOK, AC 61-27B, 5 MIN IS NEEDED FOR GYRO INSTRUMENTS TO BE OPERATIONAL. HOWEVER, THE ACTUAL TIME ALLOWED BY THE PLT (FOR THE INSTRUMENTS TO BECOME OPERATIONAL) IS NOT KNOWN.