On December 12, 1999, about 1600 Eastern Standard Time, a Pitts S-2B, N260XX, was substantially damage while landing at Northumberland County Airport (N79), Shamokin, Pennsylvania. The certificated private pilot and passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 CFR Part 91. The pilot stated that he landed on Runway 26 at N79. As the tailwheel touched down, the airplane veered to the right. The pilot applied left rudder pedal and brake, but the right main landing gear traveled into mud, and the airplane went off the right side of the runway, into a ditch. The pilot reported that he had approximately 180 hours of flight experience. Approximately 35 hours were in the accident airplane. Examination of the wreckage by a Federal Aviation Administration Inspector did not reveal any pre-impact mechanical malfunctions, nor did the pilot report any. The Inspector observed the lower left wing bent aft, and spar damage to the upper left wing. The propeller was deformed, and the left main landing gear separated from the airplane. The reported winds at an airport approximately 15 miles away were from 050 degrees at 4 knots.