The helicopter was being used to spot cattle. During what was apparently the first sweep of the area, the helicopter passed over the crest of a ridge and collided with a single power line. The angle between the fore-and-aft axis of the helicopter and the wire was approximately 40 degrees. The helicopter slid along the wire before the tail boom and then the tail rotor contacted the wire. The helicopter came to rest in a nearby gully. No fault was found in the aircraft powerplant or systems which might have contributed to the accident. Neither the pilot nor the passenger had conducted spotting operations in the area previously, and there was no evidence that either was aware of the position of the wire. It is likely that the helicopter crossed the ridge at a very low level and approximately 40 metres from a power pole carrying the wire. Background vegetation and overcast conditions may have made it difficult to distinguish the wire and power pole.