EE WAS CLEANING CRUSHED ROCK FROM A PLUGGED CHUTE AND THE ROCK HAD ACCUMLATED ONT HE CRUSHER DECK AND SURROUNDING WALKWAY. EE STEPPED ON A LOOSE ROCK, SLIPPED AND FELL ONTO THE WALKWAY STRIKIN G HIS BACK ON ONE OF THE ROCKS CAUSING A CONTUSION TO HIS LOWER BACK THE EE WAS TAKEN FOR A MEDICAL EVALUATION, PROVIDED MEDICATION AND WAS PLACED ON MODIFIED DUTIES.