On August 12, 2006, at 1830 central daylight time, a single-engine Bell 206L-1 helicopter, N601GM, was substantially damaged while landing near Ozona, Texas. The commercial pilot, sole occupant of the helicopter, was not injured. The helicopter was registered to Vista Helicopter Services, Inc., of North Las Vegas, Nevada, and was being operated by Silver State helicopters, also of North Las Vegas, Nevada. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 133 flight. A flight plan was not filed for the external load flight. The local flight originated from a nearby ranch at time unknown. The operator reported that the helicopter was in the area performing long-line (100-foot) external load operations in support of seismic activities. After landing on a uphill rocky slope, the pilot rolled the throttle to idle, friction the controls and checked the control for stability of the landing surface. The 1,263-hour commercial, who reported having accumulated a total of 48 hours in the same make and model, then exited the helicopter in an attempt to hook-up another external load bag. While the pilot was outside the running helicopter, the aircraft began to slide backwards and the pilot attempted to compensate by stepping on the toe of the landing gear skid to stop the slide. The helicopter continued to slide until the tail rotor blades made contact with a large rock outcrop. The pilot subsequently entered the helicopter, shut down the engine, and applied the rotor brake to bring the main rotors to a stop. The operator reported that the tail rotor gear box and the aft portion of the tailboom separated from the tailboom. Both tail rotor blades sustained structural damage; however, they remained attached to the tail rotor gear box. The main rotor blades were not damaged. The helicopter remained in the upright position and there was no fire. The pilot reported that at the time of the mishap, the weather was clear, with winds from the southeast at 10 to 15 knots, and a temperature of 90 degrees Fahrenheit.