THE PLT WAS ON A BANK-CHECK COURIER FLT FROM TROUTDALE TO PORTLAND, WITH EN ROUTE STOPS AT BURNS & REDMOND, OR. ROUTINELY, THE ACFT WOULD DEPART TROUTDALE BETWEEN 0900 & 0930 & ARRIVE AT BURNS AT 1130 TO 1200 LOCAL TIME. AFTER A GROUND TIME OF APRX 8 HRS, IT NORMALLY WOULD DEPART BURNS BETWEEN 1930 & 2000 LOCAL TIME. THE PLT WAS OBSERVED REMOVING SNOW FROM THE ACFT'S WING BEFORE TAKING OFF. AT APRX 2000 PST, THE PLT TOOK OFF ON RWY 12. AN IFR FLT PLAN HAD BEEN FILED, BUT WAS NOT ACTIVATED. ACCORDING TO WITNESSES, THERE WERE MARGINAL VFR CONDITIONS, REDUCING VISIBILITY WITH LIGHT TO MODERATE SNOW SHOWERS, WIND CALM TO LIGHT. SHORTLY AFTER TAKEOFF, THE ACFT CRASHED ON FLAT, SNOW COVERED, UNCULTIVATED LAND APRX 3 MI SOUTHEAST OF THE ARPT. THE IMPACT OCCURRED ON A WEST NORTHESTERLY HEADING. A PROP BLADE WAS FOUND AT THE INITIAL IMPACT POINT & THE WRECKAGE WAS SCATTERED OVER AN AREA APRX 475 FT LONG. AN EXAM OF THE WRECKAGE WAS MADE, BUT NO PRE-IMPACT MALFUNCTION OR FAILURE WAS FOUND.