On August 30, 1995, at 1630 hours Pacific daylight time, a Cessna 172A, N7641T, nosed over following a loss of control during landing at the Weed, California, airport. The aircraft was owned and operated by the left seat pilot and was engaged in traffic pattern operations during a biennial flight review. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft incurred substantial damage. The certificated commercial pilot/flight instructor and the private pilot aircraft owner were not injured. The flight originated at Dunsmier, California, on the day of the accident about 1500 and flew to Weed, where traffic pattern operations were to be conducted. In a telephone interview, the flight instructor reported that the biennial flight review was successfully completed by the aircraft owner. The flight instructor then asked the owner if he could do one takeoff and landing, to which the owner agreed. The flight instructor stated that the takeoff and pattern were normal; however, just after touchdown he began to have directional control problems and couldn't get the right rudder pedal to move beyond the neutral position. The instructor said he could not maintain directional control and the aircraft drifted off the runway edge, ran down an embankment, and nosed over after encountering large boulders. An FAA airworthiness inspector from the Sacramento Flight Standards District Office reported that no discrepancies were found in an examination of the control system.