What happened
A private certificated pilot was operating a float-equipped airplane on a flight between two remote lakes. Shortly after departing from the first lake, the aircraft's route took it across a mountain saddle located approximately five miles from the departure point. The pilot reported that the aircraft initially gained enough altitude to clear the saddle.
However, as the aircraft crossed the terrain, it encountered a violent downdraft. This encounter caused an unexpected loss of several hundred feet of altitude. The pilot was unable to arrest the descent and attempted to maneuver the aircraft to avoid a low hill. During these maneuvers, the airplane collided with tree-covered terrain on the side of the mountain and subsequently nosed over.
At the time of the accident, the pilot reported weather conditions consisting of unlimited visibility, a temperature of 50 degrees Fahrenheit, and winds from the north at 3 to 5 knots. There was no precipitation or turbulence reported at the departure point. The nearest official weather observation, located 14 miles away, had reported light rain with broken clouds at 3,000 feet and overcast clouds at 5,500 feet. The pilot did not obtain a weather briefing for the flight.