On January 2, 1994, at 1030 mountain standard time, a Cessna 140, N89036, was substantially damaged during landing at San Juan Pueblo Airport, Espanola, New Mexico. The student pilot and flight instructor were not injured. Visual meteorological conditions prevailed for the instructional flight. The instructor pilot reported that the student pilot made "three good landings." She further reported that on the fourth landing, the airplane was straight, power was off, yoke was back, and the airplane touched down softly. Almost as soon as the airplane started its landing roll, it veered to the right, departed the runway onto rough terrain, and came to rest in a ditch. The instructor applied full left rudder, but it had no effect. The instructor pilot could offer no reason why it veered right. Examination of the aircraft revealed no mechanical or structural failures that could have caused the loss of directional control.