HISTORY OF FLIGHT On June 5, 1998, about 1440 hours Pacific daylight time, a Cessna 172H, N2573L, operated by the pilot, experienced a total loss of engine power while cruising near Mariposa, California. During the pilot's forced landing about 2 miles south of the uncontrolled Mariposa-Yosemite Airport, the airplane collided with trees and was substantially damaged. The private pilot and passenger were seriously injured. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from an undetermined airport in the Bakersfield, California, area about 1400. In the pilot's report he reported that on June 4, 1998, he checked his airplane and determined that its right fuel tank was full, and the left tank was "down 2 - 3 gallons." The following morning a preflight inspection was performed, and no fuel was added. The pilot took off either "shortly after 10 o'clock" or at 1054 according to the airport's logs. The pilot stated that he flew for 1:20 hours, and landed at Bakersfield where he had lunch. Thereafter, the pilot and passenger took off for their return flight to Mariposa. The pilot did not report his departure time. He stated that while en route, he flew over Fresno at 6,500 feet mean sea level and switched fuel tanks. After flying for an additional 35 miles the engine quit, and he landed on Highway 140. The pilot and passenger and a ground-based witness were subsequently interviewed by officers from the California Highway Patrol (CHP) which provided the following additional pertinent information: (1) Passing Fresno, the fuel quantity was observed becoming low, and the right fuel tank was selected; (2) At the time, the right fuel tank's gauge indicated it was about 1/4 full; (3) After all engine power was lost, a ground-based witness heard a pilot transmit a distress call indicating that he was out of fuel; (4) During the flight between Mariposa and Bakersfield, the engine was operated at a higher than normal rpm to facilitate seating the newly installed rings and valves; and (5) The airplane's log contained a notation dated 6/5/98 with the remarks "Rings & Valves." PERSONAL INFORMATION The pilot reported that his total flight time was about 2,979 hours. He had flown the Cessna 172 for 56 hours, and his last biennial flight review was performed in a Cessna 172H. The passenger was issued a student pilot certificate on January 15, 1998. At that time, he also applied for a third-class aviation medical certificate. The examining physician declined to issue the requested medical certificate. AIRPLANE AND WRECKAGE AND IMPACT INFORMATION The Federal Aviation Administration (FAA) coordinator and the participant from the Cessna Aircraft Company examined the airplane. Neither party reported observing evidence of any preimpact mechanical malfunction. The FAA reported that the integrity of the fuel tanks, caps, and lines was established. The right and left fuel tanks were found empty, except for a small quantity of fuel present along the tanks' leading edge. A few drops of fuel were observed in the gascolator. The FAA verbally reported that the amount of fuel observed remaining in the fuel tanks was less than 1 gallon and this quantity was in the unusable range. According to the Cessna Aircraft Company, the airplane was equipped with standard 39-gallon capacity fuel tanks. In all flight attitudes, 36 gallons of fuel are considered usable. ADDITIONAL INFORMATION The pilot indicated in his report that no mechanical malfunctions or failures were experienced during the flight. Also, he reported that the accident could have been prevented had he refueled (before takeoff) at Bakersfield.