EE WAS OPERATING THE 2500 HITACHI EXCAVATOR APPROX. 70 FEET FROM THE HIGHWALL. HE WAS REACHING INTO THE OVERBURDEN TOWARD THE HIGHWALL WHEN THE WALL BEGAN WORKING. SMALL ROCKS AND DUST BEGAN F ALLING ONT HE CAB AND HE GOT OUT OF THE SEAT TO MOVE AWAY FROM THE FRONT GLASS. AS HE WAS MOVING TOWARD THE BACK A ROCK MEASURING 8 FEET LONG 3 FEET TALL AND ABOUT 4 FEET WIDE FELL FROM THE H