On February 4, 1996, approximately 1000 Pacific standard time, a Cessna 172M, N6750H, being flown by a private pilot, sustained substantial damage when it collided with a tree top while in cruise on the lee side of Capitol Peak, approximately 6 nautical miles west of the Olympia airport, Olympia, Washington. The pilot reported visual meteorological conditions at the time of the accident. No flight plan had been filed. The pilot and three passengers were uninjured. The flight, which was a personal sightseeing trip, was to have been operated under 14CFR91, and originated from Tacoma, Washington, approximately 0900. In a telephone interview, the pilot reported that he crossed Capitol Peak (elevation approximately 2,660 feet above sea level) approximately 400-500 feet above the terrain, headed eastbound, at approximately 65 percent power and immediately thereafter encountered a downdraft. The aircraft descended to tree top level and impacted a tree. Subsequent to the collision the pilot determined that the aircraft had sustained leading edge damage to its right wing from a point just forward of the strut attach point outboard for approximately 2 feet. He then diverted into Olympia landing approximately 1015. The pilot reported westerly winds of 15 knots gusting to 20 knots at the time of the accident. The forecast winds at Seattle at 3,000 feet above sea level were for the morning of the accident were from 300 degrees true at 17 knots.