The helicopter was following participants in a downhill skateboard race in mountainous terrain. The pilot had just performed a left pedal turn and the helicopter was facing upslope to the mountain. The low rotor warning sounded and the pilot lowered collective and increased throttle. The pilot stated that the engine did not respond so he continued to lower the collective and looked for a place to land. During the forced landing on the down sloping terrain, the helicopter came to rest on its nose resulting in substantial damage to the main rotor, skid tubes, and tail boom. An examination of the helicopter, engine, and systems, conducted by the Federal Aviation Administration, revealed no anomalies. The density altitude was calculated to be 10,600 feet. The pilot calculated the in ground effect hover to be 8,500 feet pressure altitude, the out of ground effect hover to be 5,000 feet pressure altitude, and estimated the gross weight to be 2,320 pounds.