On March 15, 1997, at 1328 central standard time, a Cessna T210, N6677N, operated by a private pilot experienced a left main landing gear collapse during takeoff roll at Rock County Airport, Janesville, Wisconsin. The personal 14 CFR Part 91 flight was operating in visual meteorological conditions without a flight plan. The airplane was substantially damaged and the pilot was not injured. The pilot reported that during the takeoff roll on runway 31 (5,396' x 150') the left main gear collapsed at an airspeed of 60 to 70 knots. According to the mechanic who retrieved the airplane after the accident, the airplane veered about 20 feet off the left side of the runway coming to rest approximately 2,000 feet down the runway near the intersection of runway 31/13 and 04/22. Inspection of the airplane by an A&P/IA mechanic from Terry's Aero, Inc., who removed the airplane revealed the outboard leading edge of the left wing was crushed back 5 to 6 inches, the propeller was damaged, the nose gear doors were bent, the bottom of the fuselage sustained skin damage and the lower left portion of the firewall was damaged. He stated the nose gear was pushed up in the wheel well and the left main gear was pushed up. The landing gear selector handle was in the down position. He stated that when the airplane was lifted off the runway the left main gear and the nose gear were easily extended. The landing gear was cycled by this mechanic under the supervision of a Federal Aviation Airworthiness Inspector from the Milwaukee Flight Standards District Office. The landing gear operated normally during the functional tests.