DRIVER EXPLAINED THAT HE FELT HE WAS PARKED ON A LEVEL SURFACE. WHEN RAISING THE BED HE FELT THE BED SHIFTING AND TRIED TO LET IT DOWN BUT IT WAS TOO LATE AND THE CAB AND TRAILER TIPPED OVER. HE ALSO FELT THAT THE WIND CONTRIBUTED TO THIS. MY INVESTIGATION SHOWED THAT THE SURFACE THE TRUCK WAS PARKED ON WAS UNEVEN, THE ROCK BEING DFUMPED WAS CLEAN AND DRY, THE GROUND AREA WAS SOLID