On January 6, 1996, approximately 1330 mountain standard time, a Cessna 172K, N172NS, registered to Northern Skies Aviation of Laurel, Montana, received substantial damage in an inflight collision with an object. The pilot reported that the inflight collision occurred approximately 2 to 5 miles north of Park City, Montana. Following the occurrence, the flight returned to Laurel and landed without further incident. Neither the private pilot nor his passenger were injured. The 14 CFR 91 flight had been planned as a local flight out of Laurel. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot stated in his accident report: I departed Laurel Municipal Airport (6S8) at approximately 1300....We had been flying for about half an hour when we decided to descend in order to get a better view of the landscape....[We descended] to between 4,100 and 4,300 [feet] MSL, in order to fly through the various valleys between the plateaus present north of Park City....We had been down there only briefly when we heard something strike the aircraft. (It felt like driving a car over [railroad] tracks[.]) Neither of us had seen any obstacles that may have hit the plane. I immediately checked all of the controls and found that the plane still flew normally, so we flew directly back to Laurel and landed. Once on the ground, it was determined by the nature of the damage (a slice in the vertical fin, plus two broken antennas) that it was a wire strike that occurred. I believe this accident was a result of failure on my part to maintain sufficient altitude. Photographs showed the vertical fin damage to be a gash approximately 8 inches deep and 12 inches below the top of the stabilizer. The gash extended approximately straight back from the vertical tail leading edge into the tail, approximately parallel to the aircraft longitudinal axis. An antenna on the upper surface of the aircraft, at approximately the left wing trailing edge, was also broken back at its base. The Billings sectional aeronautical chart shows the ground elevation in the vicinity of the reported wire strike as approximately 4,000 feet above mean sea level. The pilot reported in a telephone conversation with the investigator that his altitude above the ground at the time of the strike was approximately 100 feet and that he was flying in a valley with high terrain on both sides of the aircraft.