On September 8, 1996, at 0909 hours Pacific daylight time, a Stinson 108, N97337, experienced a power loss and forced landing after takeoff from Gansner Field, Quincy, California. The aircraft sustained substantial damage and the private pilot received minor injuries. The aircraft was operated as a personal flight by the pilot/owner when the accident occurred. The flight originated in McCall, Idaho, the day before the accident with an overnight stop in Denio, Nevada. The flight resumed at 0600 on the morning of the accident. The pilot landed at Gansner Field and was on departure when the accident occurred. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot reported he leaned the engine prior to taking off on runway 24. The engine performed normally during the run-up and takeoff roll, but quit as the aircraft reached about 50 feet agl. He switched tanks, moved the mixture control to the full rich position, and pumped the throttle twice before attempting to restart the engine. On his first attempt, the engine started but ran only for a few seconds before quitting again. A second attempted restart was unsuccessful. He executed a forced landing in an open field on the opposite side of state highway 70. During the landing roll the aircraft struck a log with the right main gear. Damage to the aircraft included a collapsed right main gear, fuselage buckling aft of the main wings, and bent propeller blades. The pilot told FAA inspectors that he could have induced the problem initially by over leaning the engine. He also said that he could have restricted the fuel flow when he inadvertently moved the fuel selector beyond the tank detent position. During their postaccident examination, inspectors found no discrepancies in the fuel system, with fuel available in both tanks as well as in the carburetor. An inspection of the aircraft logbooks revealed that the aircraft had not undergone an annual inspection within the last 12 calendar months. In addition, the pilot reported that he was using a mixture of aviation fuel and auto gas. The aircraft did not have an STC authorizing the use of auto gas. The pilot was flying with an expired medical certificate.