On July 16, 1996, at 0740 hours Pacific daylight time, a Cessna 172N, N738NZ, collided with a berm while attempting a forced landing on a desert road near Daggett, California. The forced landing was precipitated by a loss of power during cruise. The aircraft was operated by Barstow Aviation of Daggett, and was rented by the pilot for a local area personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft incurred substantial damage. The certificated private pilot, the sole occupant, was not injured. The flight originated at Daggett on the morning of the accident at 0700. The pilot reported that he was in cruise flight when the engine suddenly ran rough and lost power. The pilot attempted to land on a desert road; however, the road curved more than the aircraft could turn at the speed it was traveling after touchdown and the aircraft left the road and hit a berm. During recovery operations an exhaust valve head fell out of the exhaust stack. Maintenance personnel reported that the fracture faces on the head and corresponding stem were obliterated due to peening. The engine was overhauled about 24 hours prior to the accident.