Abstract: Employee #1 and coworkers were assigned to remove some rocks from immediately below the Beaver City penstock to clean and reinforce the channel. A winch truck was on the north shoulder of an asphalt road that ran parallel to the stream bank and a pulley had been placed around and into an opening in a solid rock face that was approximately 35 ft from the stream bank. A 1/2 in. wire rope was let out, run through the pulley, and then run to a roughly 35 percent slope about 60 ft upstream; an eyelet was bound on the end using three clamps. A chain with 3/8 in. links had been wrapped four times around a rock to be moved. As the rock was lifted, it became caught on another rock. When the tension increased, the chain slipped away from around the rock being lifted and the rock was thrown approximately 30 ft, striking Employee #1. He sustained injuries that required hospitalization.