On May 30, 2003, at approximately 0900 mountain daylight time, a Hiller UH-12E helicopter, N508SQ, was substantially damaged when it impacted terrain while maneuvering south of Cheyenne, Wyoming. The commercial pilot, the sole occupant on board, was not injured. Reforestation Services, Inc., of Salem, Oregon, was operating the helicopter under Title 14 CFR Part 137. Visual meteorological conditions prevailed for this local aerial application flight, which originated approximately 15 minutes prior to the accident. The pilot had not filed a flight plan. According to the pilot, he was spraying vegetation along the Union Pacific railroad tracks. He was reversing course for a second application pass and began a "cyclic climb/ag turn" when he encountered a gust of wind, "approximately 15-20 miles per hour," from his "6 o'clock position." The pilot stated he was unable to recover before he hit the ground. Subsequently, the helicopter rolled on its right side, and the main rotor blades separated. An examination of the helicopter's systems revealed no anomalies. At 0911the Aviation Routine Weather Report (METAR) from Cheyenne reported winds from 320 degrees at 12 knots with gusts to 17 knots.