Abstract: At 9:40 a.m. on March 29,2011 Employee #2 reported that Employee #4 was struck by a hopper from a rock crusher and suffered a severe laceration to the Right leg At the time of the injury Employee #4 was involved in removing the lower hopper from the rock crusher. Employee #4 received emergency medical treatment from the Lakeside Fire Department and was transported to the Hospital where he was treated and hospitalized in excess of 24 hours. Employer # 2 reported the injury within 8 hours of knowing it would be a serious injury in compliance with T8 342(a). The employees were doing construction work at the San Vicente dam in Lakeside, CA. The company is raising the height of the existing dam 117 feet. The work being done by employees #4 and #5 at the time of the accident was being done at the rock crushing operation for the project. On the day of the accident Employees #4 & #5 had removed a discharge hopper from the bottom of the rock crusher that directed the crushed material to a conveyor belt located at the bottom of the rock crusher. Employee #7 estimated the weight of the hopper and dirt attached to it to be approximately 700 pounds. Employees #4 & #5 stated that they had removed the hopper from the crusher and that it was sitting/resting on the conveyer's metal side rails, the conveyor belt and the tail pulley guard. Additionally a nylon web ratchet strap was attached to the hopper for support. After the hopper was placed on the conveyor belt components Employee #4 walked behind the tail pulley guard to retrieve a chain used in the removal process. At this same time the hopper moved forward, on to the slopped tail pulley guard and slide off the guard striking Employee #4 and pinning him to the ground.