On September 23, 2005, about 1230 Pacific daylight time, a Piper PA-18-150, N5756Y, veered off the runway and impacted flat level terrain at Fall River Mills Airport (O89), Fall River Mills, California. The pilot/owner operated the airplane under the provisions of 14 CFR Part 91 as a personal cross-country flight. The airplane sustained substantial damage. The private pilot and one passenger were seriously injured. Visual meteorological conditions prevailed for the flight, and no flight plan had been filed. The flight departed the King City, California, airport at an undetermined time. A refueling stop was made at Red Bluff Municipal Airport, Red Bluff, California. The flight departed Red Bluff about 1200, and was destined for O89. In a written statement to the National Transportation Safety Board, the pilot reported the accident occurred during landing. Upon arrival at the airport he entered the pattern for left traffic for runway 2. He attempted to land and lost directional control after encountering an "extreme" left crosswind. The aircraft came to rest approximately 200 feet east of the runway. The pilot reported no mechanical anomalies with the airplane.