Abstract: At approximately 1:00 p.m. on October 4, 1996, a loader operator informed the plant manager about a dangerous overhead rock adjacent to where he was loading pit trucks with shot rocks at the west end of the rock quarry pit floor. The plant manager ordered the pit crew away from the dangerous area and told Employee #1 to knock down the rock point as soon as he finished the area he was leveling. At approximately 1:50 p.m., while Employee #1 was traversing the 20 ft wide offset safety bench in a Caterpillar D10N tractor, serial #SYD01610, to push down the high wall rock point to the pit floor. He was at an elevation of 710 ft when the outside edge of the bench under the tractor's right track failed and the right rear of the tractor dropped down the slope. As the outside 10 ft of the bench at this faulted zone gave way under the weight of the machine, the tractor slid halfway down the 40 ft high bench. It remained skewed for 20 seconds before it rolled over and continued to fall, upside down, until it struck the quarry floor. The impact of the fall indented the steel plate on the right-hand corner of the roof's roll-over protection structure. Employee #1 suffered extensive injuries, including a concussion, lacerations on the scalp and face below the left ear, fractured right ribs, and cuts and bruises all over his body. He was transported to John Muir Hospital, where he was released after eight days. Employee #1 could have avoided injury by wearing his seal belt more snugly. He admitted that he wore his seat belt loosely to afford him some freedom of movement to maneuver his equipment controls and to be able to turn his back to see where he was going when he was travelling backward.