On March 7, 2004, at approximately 1130 mountain standard time, a Cessna 182P, N29821, piloted by a private pilot, sustained substantial damage when during a landing on a dirt road, 38 miles southwest of Hanksville, Utah, the airplane nosed over. The pilot and pilot-rated passenger were not injured. Visual meteorological conditions prevailed at the time of the accident. The personal flight was being conducted under the provisions of Title 14 CFR Part 91. No flight plan was on file. The cross-country flight originated at Marble Canyon, Arizona, and was en route to Cedar City, Utah. During an interview, the pilot reported that he and his wife were sightseeing. He said they had been airborne approximately 2 hours when the airplane's engine began running rough. The pilot said he checked his magnetos, the fuel tanks, the mixture, and propeller, and adjusted the throttle. None of these actions seemed to work. The pilot said he decided to put the airplane down on a dirt road. He said that as he was about to land, he noted that the road was narrower than he thought. The pilot said the road was soft. The airplane slowed down, but then the nose wheel dug into the soft dirt and the airplane flipped over. In his statement written statement, the pilot described the issue with his engine as a "vibration." He reported that he attempted to isolate the problem without success. He said the vibration "persisted to the point that he became afraid to continue the flight." An examination of the airplane at the accident site showed that the cowling was crushed aft, both wings were bent downward and aft, and the vertical stabilizer and rudder were crushed downward. The propeller showed torsional bending and chordwise scratches. Flight control continuity was confirmed. The airplane wreckage was retained for further examination. The airplane's engine was successfully test run on March 17, 2004, at Spanish Fork, Utah. An examination of the other airplane systems revealed no anomalies.