On September 2, 1996, at 1530 Alaska daylight time, a wheel equipped Cessna 206 airplane, N733KD, registered to and operated by Lake Clark Air, Inc., collided with terrain and nosed over after entering and maneuvering in a narrow canyon. The air taxi flight, operating under 14 CFR Part 135, departed Port Alsworth, Alaska, and the destination was Lake Tazimina near Port Alsworth. A company visual flight rules flight plan was in effect and visual meteorological conditions prevailed. The airline transport certificated pilot and the passenger were not injured. The airplane received substantial damage. According to the pilot, he allowed the passenger to talk him into flying up the narrow canyon which appeared to be a pass at the time he entered. After entering the canyon he realized he would be unable to make a 180 degree turn and he applied maximum power. The terrain was rising steeply and he was attempting to reach the top of the pass. The airplane contacted the ground at the 2,800 foot level of the pass. The pilot stated the pass was 3,000 feet high. After the airplane's floats hit the ground, the airplane slid approximately 15 feet. The nose of the floats dug into the dirt and the airplane nosed over.