EMPLOYEE WAS USING A HOSE TO CLEAN UNDER THE JAW BELT CONVEYOR WHICH IS TWO FEET OFF THE GROUND. HE WAS STANDING BELOW & TO THE SIDE OF THE HEAD SECTION OF THE 5 1/2 DISCHARGE BELT & THE TAIL SECTION OF THE 5 X 14' CONVEYOR. THE BELTS WERE OPERATING & A ROCK FELL FROM ONE OF THESE BELTS APPROXIMATELY 10' & STRUCK HIS BACK. HE IS LOSING TIME.