On May 17, 2010, approximately 1853 central daylight time, a Cessna P206B, N50LP, was substantially damaged upon impact with terrain near Spring Branch, Texas. The private pilot and passenger sustained minor injuries. The airplane was owned and operated by a private individual. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The local flight departed the Kestrel Airpark (1T7), San Antonio, Texas, at 1756. In a telephone interview conducted with the pilot, the pilot and passenger were performing a maintenance test flight and were returning to the airfield. While descending through 2,500 feet mean sea level, the airplane's engine abruptly lost total power. The pilot switched fuel tanks and attempted to restart the engine but was unsuccessful. The pilot radioed a distress call to the airport, which was received by airport personnel. Due to proximity to the ground, the pilot stopped further engine troubleshooting, and elected to conduct a forced landing to an open field. A row of trees blocked the airplane's path during the forced landing, so the pilot maneuvered the airplane but the airplane impacted terrain. Damage was sustained to the airplane's fuselage and wing spar. During recovery of the airplane, the recovery crew drained approximately 10 gallons from the right fuel tank and found the left fuel tank empty. The airplane wreckage was examined by the National Transportation Safety Board (NTSB) with technical assistance provided by Cessna Aircraft and Teledyne Continental Motors. An examination of the engine did not reveal any anomalies which would have precluded normal engine operation. An examination of the airplane's fuel system revealed debris partially obstructing the filter of the fuel mixture unit. No other filters contained this debris and the source of the debris could not be determined. The fuel lines were opened and absent of fuel from the auxiliary fuel pump to the fuel manifold. Fuel was found within the fuel manifold. No other anomalies were discovered with the airframe. The examination of the engine did not reveal any anomalies which would have precluded normal engine operations. A review of data downloaded from the GPS unit revealed that the pilot departed the airport at 1756 and flew towards Hondo, Texas, before heading north to Boerne, Texas, before attempting to return to 1T7. The last GPS point recorded a speed of 65 knots, 68 feet above ground level descending approximately 700 feet per minute. The airplane maintenance records were not recovered during this investigation. The most recent annual inspection could not be determined. The owner did not return a NTSB Form 6120.1 prior to the completion of this investigation.