On September 17, 2018, at 1335 Pacific standard time, a Piper PA-24-250, N7472P, was substantially damaged when it was involved in an accident near Upland, California. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. The flight originated from Reno/Tahoe International Airport (RNO), Reno, Nevada, about 1115, where the airplane had been tied down for four days. On the morning of the accident, the pilot performed a preflight inspection and noted no discrepancies. The airplane’s auxiliary fuel tanks had been fueled with 20 gallons of fuel; 10 gallons in each auxiliary tank. The pilot estimated a total of 75 gallons of fuel onboard at the time of departure. The pilot stated that he departed with the left main fuel tank selected and estimated that it contained about 30 gallons of fuel. Once he reached cruise altitude, he switched to the right auxiliary fuel tank and alternated between the left and right auxiliary tanks every 30 minutes until there were about 5 gallons remaining in each auxiliary tank. He used the electric fuel pump during each fuel tank change. About 3.5 nautical miles (nm) from the destination airport, the pilot turned on the electric fuel pump and switched to the right main fuel tank. He noted that the fuel pressure was steady, and he left the electric fuel pump on for the remainder of the approach. As he turned from the crosswind to downwind legs of the traffic pattern, he extended the landing gear and performed the before landing checklist. While on final approach for landing, he noted an increasing sink rate, and increased the throttle to compensate; however, there was not a corresponding increase in engine power. He switched to the left main tank, confirmed that the electric fuel pump was switched to ON, the ignition switch was on BOTH, fuel mixture control was full-rich, and that the propeller control was in the maximum rpm position, but the engine did not respond. The pilot chose an empty field short of the runway in which to perform a forced landing. The airplane rolled a short distance before the nose landing gear and the left main landing gear impacted rocks and the airplane spun about 150° before coming to a stop. The pilot reported that he was wearing a noise-cancelling headset and wasn’t sure when the partial loss of engine power occurred. A responding Federal Aviation Administration (FAA) inspector reported that the main fuel tanks contained 24 to 25 total gallons of fuel. A visual inspection of the engine revealed no holes in the case. Valve train and mechanical continuity was established throughout the engine. The oil filter was examined with no carbon deposits found. The fuel screens for both boost pumps were free of debris. The aft boost pump contained about 4 spoonsfuls of a mixture of fuel and water. Borescope examination of the cylinders revealed signatures consistent with a lean fuel/air mixture.