On February 20, 2002, approximately 0800 Pacific standard time, a Cessna 172, C-FISS, registered to and operated by a private individual, and borrowed/being flown by a Canadian certificated commercial pilot, was substantially damaged during an in-flight collision with trees and subsequent collision with terrain while maneuvering. The pilot, who was the only occupant aboard the aircraft, was uninjured. The accident site was located three nautical miles east of Concrete, Washington, at an elevation of 850 feet above mean sea level. The pilot reported scattered clouds and rain showers at the time of the accident, and no flight plan had been filed. The flight, which was personal, was operating in US airspace under 14CFR91 at the time of the accident. The flight departed Langley, British Columbia, approximately 0700, destined for Chilliwack, British Columbia, approximately 27 nautical miles to the east-northeast of Langley. The pilot hiked out from the accident site and reported the accident to law enforcement officials with Skagit County. The pilot was subsequently interviewed on February 22 and submitted a written statement as part of his NTSB Form 6120.1/2 (both attached). He reported that he departed Langley, British Columbia (BC), en route to Chilliwack, BC, and decided to detour into US airspace in the vicinity of the Skagit River following it until reaching Lake Shannon and then returning to Canada. He continued, reporting that he was flying about 1500 feet in elevation roughly eastbound along the river (the River's approximate elevation between 200 and 300 feet above sea level near Concrete). Passing Concrete he noted rain showers ahead and decided to make a 180-degree turn for the return leg. He indicated that he had been using carburetor heat without problems and noted no engine performance problems during the flight. He executed a left turn at 75 miles per hour utilizing two "notches" (20 degrees) of flaps. During the turn he noted a loss of altitude and compensated with power. As the sink rate continued he raised the flaps to one "notch" (10 degrees) and applied full power. He indicated that the sink rate continued and reported in his interview that it "felt like the aircraft was getting sucked down." He reported that as the turn progressed he could see trees and rising terrain ahead, which he tried to avoid. And, that when he determined impact was unavoidable he pulled back on the control column to execute a controlled stall into the trees (refer to NTSB Form 6120.1/2 and ATTACHMENT PI-I). The pilot provided a diagram showing his track over the ground superimposed on a topographic map of the vicinity of the accident site (refer to NTSB Form 6120.1/2). This diagram, along with CHART I (attached) showed the aircraft commencing its left turn about two nautical miles east of Concrete and turning towards rising terrain. The gradient of the terrain rise to the north (direction of the turn) was considerably steeper than the gradient to the south. The pilot also reported that he believed he had encountered a severe downdraft in the vicinity of the accident site.