On September 12, 2003, approximately 0920 Pacific daylight time, a Bell 47G-3B-1, N48020, registered to the pilot, doing business as High Desert Helicopters as a 14 CFR Part 91 flight for the purpose of herding horses into a trap for the Bureau of Land Management, landed hard near Diamond, Oregon. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight. The helicopter was substantially damaged and the commercial pilot, the sole occupant, was seriously injured. The flight had been operating in the area for about twenty minutes prior to the accident. In a written statement, the pilot reported that he was in a hover about 80 feet above ground level observing the horses that he was herding into a trap. The pilot stated that as he started to transition from the hover to forward flight, he noticed that the rotor rpm was decaying and the engine rpm increased rapidly. The pilot immediately rolled the throttle off and reduced collective pitch to enter an autorotation. Due to the decreased airspeed, the helicopter descended rapidly. Approximately 20 to 30 feet agl, the pilot added collective pitch control to control the rapid descent, however the helicopter landed hard. The main landing skids collapsed and the main rotor blades contacted and severed the tail boom. The helicopter came to rest with the engine still running on its tail and left side, nearly inverted with the nose high. A ground crew member (wrangler) in the local vicinity aided the pilot and was instructed to turn off the magnetos. Several people involved with the herding of the horses reported that they did not see the crash sequence due to terrain. Several did hear the helicopter's engine noise change to a "high pitch" sound just before the sound of the collision. An individual video taping the herding activity captured the sound of the helicopter engine, however, due to the terrain, did not have the aircraft in sight. The video verifies the engine sound going from a normal sound to a sudden high pitch, followed immediately by the sound of the collision. At the time of the accident, the temperature was reported at 65 degrees F. The wind velocity was about 8 knots, with gusts to 12 knots. The altimeter setting was 29.98" Hg. The accident site elevation is 4,700 feet mean sea level. Density altitude for the reported conditions were calculated as 6,087 feet. The wreckage was removed from the accident site and transported to Fallon, Nevada. An inspector from the Reno, Nevada, Flight Standards District Office inspected the helicopter. The inspector reported that the engine, transmission, clutch and freewheeling systems were inspected. No evidence of a mechanical failure or malfunction was found. The tach indicator was found inoperative and sent out to a facility for inspection. During the inspection it was found the unit was bound from impact damage.