On February 22, 1998, at 1715 hours Pacific standard time, a Schempp-Hirth Ventus-B glider, N948B, collided with a drilling rig while turning from left base to final at the Williams, California, airport. The aircraft sustained substantial damage and there was minor damage to the rig. The private pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed for the personal flight and no flight plan was filed. The local flight initiated at 1230 and was terminating at the time of the accident. The pilot reported that there was a drilling rig parked approximately 30 to 40 feet from the end of the runway and he was aware of the location of the rig before takeoff. He further stated that he usually placed a wooden wedge behind the landing gear handle to secure it in place before landing, but while on final he noticed that he had not yet secured it. While he attempted to secure it in place, he noticed that the aircraft had a "very great rate of descent." He then "concentrated in controlling the direction of the aircraft to land properly on the runway, looking ahead and losing reference of the drilling rig." The right wingtip then hit the upper portion of the rig and approximately 3 to 4 feet of the wing separated from the aircraft, and the nose of the glider hit the ground. The glider spun to the right approximately 180 degrees before coming to a complete stop.