On May 21, 1993, at about 1335 hours Pacific daylight time, a Piper PA18 150, N9461P, ground looped and nosed over on landing at the Nut Tree airport, Vacaville, California. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft incurred substantial damage. The certificated private pilot was not injured. The local area pattern practice flight originated at Vacaville, California, on the day of the mishap at about 1300 hours. An FAA inspector witnessed the accident. He reported that the aircraft was landing on runway 20 with a right 45 degree cross wind he estimated at 14 knots with higher gusts to about 17 knots. Shortly after touchdown, the aircraft ground looped and nosed over. The inspector stated that he routinely flies into and out of the airport, and, due to some trees bordering the airport, the wind conditions can sometimes be highly variable with wind shears and vortex situations. The FAA inspector reported that he examined the pilot's logbook. All of the pilot's flight time was accrued in tail wheel aircraft.