OPERATOR WAS BERMING NEW PROPERTY THAT HAD PREVIOUS DIRT EXCAVATING ACTIVITY ON IT. OPERATOR WAS BLOCKING AN EXISTING RAMP. AS HE BACKED DOWN, HIS LEFT REAR TIRE DROVE OFF THE RAMP, APPROX A 2 FOOT DROP. THE WEIGHT OF THE LOADER SHIFTED TO THE LEFT REAR & THE LOADER LAID ON ITS LEFT SIDE.