The pilot was flying the helicopter along a ridge line checking a gully for cattle, when the engine suffered a substantial loss of power. The pilot initiated an autorotational descent as the engine failed completely. The helicopter landed heavily in the base of the gully. The pilot was aware that there was little fuel remaining in the tank. However he elected to continue and ensure the security of the mob before last light, so that additional herding would not be necessary the next day. The helicopter was being operated at a low height and airspeed, over unsuitable terrain at the time the fuel was exhausted.
