On March 16, 2000, approximately 1030 mountain standard time, a Piper PA-18-150, N2873Z, experienced a gear collapse during the landing roll at Three Forks Airstrip, Three Forks, Montana. The commercial pilot and his passenger were not injured, but the aircraft, which was owned and operated by the pilot, sustained substantial damage. The CFR Part 91 personal pleasure flight, which departed Bozeman, Montana, about 45 minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT activation. According to the pilot, he "stalled" the aircraft onto the main gear and then lowered the tailwheel to the runway surface within 50 to 100 feet. He said that when the tailwheel touched down, the aircraft started pulling to the left as if he was applying "slight left brake." He applied significant right rudder in an attempt to return the aircraft to the center of the runway, but the aircraft still drifted to the left. As he was slowing, the aircraft suddenly turned to the right "...as though the left brake released or the tailwheel unlocked." Although he attempted to keep the aircraft aligned with the runway, the aircraft goundlooped to the right, resulting in the collapse of the left landing gear and damage to one of the wings. The pilot reported that there appeared to be no problems with or malfunction of any of the aircraft's directional control systems. The final line of his accident narrative stated, "Bottom line was failure to maintain directional control." The pilot also reported that he inspected the brakes after the accident and found "... no visible signs of malfunction."