On June 25, 1995, approximately 0810 hours Pacific daylight time, a Cessna 150M, N66727, being flown by a private pilot, was substantially damaged during a collision with trees/terrain while turning to reverse course over mountainous/hilly terrain approximately 5 nautical miles east of Meachem, Oregon. The pilot was seriously injured. Visual meteorological conditions prevailed and no flight plan had been filed. The personal flight was to have been operated under 14CFR91, and originated from Pendleton, Oregon, approximately 0740. The pilot reported that while returning to Pendleton "over the gorge near Meachem Creek" he experienced a "downdraft and applied more power to keep from losing altitude." He reported that his airspeed decayed to less than 75 mph and he "eased the nose forward and applied more power (not full throttle)." He reported that "By this time (he) had lost considerable altitude and was barely above tree top level." To avoid hitting the trees he "pushed the throttle in all the way, and banked sharply to the left. The right [sic] wingtip hit the ground and the aircraft cartwheeled, while sliding sideways into the trees." Winds at the Meachem reporting station were less than 5 knots throughout the morning of the accident.