The pilot reported that during the landing rollout on a dirt runway, the airplane struck something. The airplane veered off the runway, bounced over a berm, and struck a small ditch that sheared off the nose landing gear and damaged the left wing tip. He reported that the runway was located in a remote area near a mill. The desert floor had been graded to make it usable as a runway. A mechanic at the mill had driven along the runway prior to the accident flight, and reported no disturbances on the runway to the pilot. The mechanic further reported that it looked okay to land there. The pilot stated that he has landed on this runway several times with no problems encountered. The pilot also reported that there were no mechanical problems with the airplane.