An employee was hauling material to the back of the yard using a truck and end dump trailer. After dumping the material, the protective tarp caught on the tailgate and prevented it from fully closing. As the employee removed the tarp from the tailgate, his left hand was caught in a pinch point between the tailgate and the trailer frame when the tailgate dropped. His left hand was crushed resulting in injury to several bones and ligaments. His left wrist was also lacerated and fractured.