The pilot was taking off from an off-airport landing site near the top of a mountain ridge, in gusty wind conditions, in a tailwheel-equipped airplane. During the takeoff roll, a gust of wind pushed the airplane onto rough terrain, which resulted in the airplane becoming airborne before it had sufficient speed to maintain flight. When the airplane settled back to the ground, the main landing gear broke off, and the airplane nosed over, sustaining substantial damage to the wings and empennage. The pilot reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.