On July 7, 1997, at 1100 hours Pacific daylight time, a Cessna 150G, N458AE, departed the taxiway, collided with a sand dune, and came to rest inverted at the Barstow-Daggett, California, airport. The aircraft sustained substantial damage, and the student pilot/owner, the sole occupant, was not injured. Visual meteorological conditions existed for the instructional flight that originated from the Needles, California, airport at 0955. Witnesses to the accident reported that the aircraft was taxiing to the active runway (runway 26) when the aircraft veered off the taxiway, hit a sand dune, and nosed over. In an interview with an Federal Aviation Administration (FAA) inspector, the pilot reported that he had landed at the Barstow-Daggett airport to refuel his aircraft before continuing his flight to the Van Nuys, California, airport. The pilot claimed that during the taxi he checked the aircraft brakes and that is when the right brake failed. The pilot reported that the left brake worked and caused the aircraft to veer to the left and depart the taxiway. An FAA airframe and powerplant mechanic with inspection authorization examined the aircraft after the accident. He reported that the right brake functioned normally, but that the left parking brake spring was not adjusted properly, allowing the left brake to be activated at all times. No other preexisting anomalies were found. The pilot did not respond to repeated written and telephone inquiries for a statement and the aircraft maintenance records.