On May 20, 2006, approximately 1400 mountain daylight time, a Cessna 172M, N12808, departed the runway during the landing roll, and collided with the terrain of a nearby ditch at Ravalli County Airport, Hamilton, Montana. The private pilot and his three passengers where not injured, but the aircraft, which is owned and operated by Northstar Aviation, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Bozeman, Montana, about 90 minutes prior to the accident, was being operated in visual meteorological conditions. The aircraft had been on a visual flight rules flight plan. According to the pilot, as he neared the airport he was advised by the UNICOM operator that the winds were 270 degrees at 15 knots, gusting to 25 knots. As he rolled out on a left downwind for runway 16, the pilot determined that there was a strong crosswind due to the amount of crab required to hold a ground track parallel to the runway. As the pilot was turning onto final, the UNICOM operator advised him that at that point in time, the winds were blowing at 10 knots. In order to maintain the proper ground track on final, the pilot crabbed the aircraft into the wind, and then switched to a wing-low forward slip on short final. Although the touchdown was uneventful, about 50 feet into the ground roll, the aircraft encountered a strong crosswind gust from the right. The pilot was unable to adequately compensate for the effects of the gust, and the aircraft's right wing lifted, and the aircraft headed toward the left side of the runway. After departing the runway, the aircraft entered a large ditch, impacting its far side with sufficient force to result in substantial damage. After the accident, it was determined that due to building weather in the nearby mountains, the winds in the area were almost constantly changing direction and velocity.