On July 5, 1997, approximately 1100 mountain daylight time, a Piper PA-18-150, N4249Z, registered to and being flown by a private pilot, was substantially damaged during an inflight collision with terrain while maneuvering in the vicinity of Mile High airstrip, Big Creek, Idaho. The pilot was uninjured. According to the pilot, visual meteorological conditions prevailed, and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and originated from Johnson Creek airstrip, Yellow Pine, Idaho, approximately 1000. The pilot reported that he "circled Milt Hi (airstrip) with the intent to look at a super cub wreckage (N27296) on top of the ridge" and that while circling, and on the north (lee) side of the airstrip/ridge he "lost altitude and wound up having to flare to 'land." The pilot stated that "at that point my intent was to coast over the ridge and take off on the upwind slope." The pilot further stated that as the aircraft reached to the top of the ridge "it abruptly turned to the right '(probably due to the wing coming up the slope)' and yawed right." He indicated that subsequently crossed the top of the ridge airborne, descended and struck the ground collapsing the left main landing gear at an estimated airspeed of 20-25 miles per hour (refer to photograph 1). The Mile Hi airstrip is considered a US Forest Service Emergency strip. It has no identifier and is situated at an elevation of 5,831 feet above sea level (refer to ATTACHMENT I). The strip is unidirectional with landings towards 190 degrees magnetic and takeoffs in the reverse direction. The landing direction provides a 15-22 percent uphill grade of approximately 560 feet length followed by an approximate 45 degree dogleg "run-out" to the right. The pilot estimated the winds at the accident site as 130-140 degrees at 5 to 10 knots, and the temperature at 80 degrees Fahrenheit. The approximate density altitude based on that temperature, elevation and a standard pressure setting of 29.92 inches of mercury was 8,700 feet.