The pilot was moving logs during an external load operation in a mountainous, burned out, wooded area. The elevation was about 4500 ft. Logging crews observed the helicopter approach the "log landing area" while hauling a load of logs with a 160 ft cable. They reported that the helicopter was coming in for another "turn of the logs" (a drop). The director of maintenance stated this was the pilot's fifth "turn" with this hook and line assembly. A witness reported the helicopter tail boom dropped downward after turn of the logs, veered to the left and right erratically, yawed left, and crashed. One witness stated in part "the turn hit the landing and I concentrated on the chokers the loader had. Then I saw the turn of logs jump 20 - 30 ft across the landing." During the crash, the helicopter struck trees, impacted the ground, and burned. All instruments and controls were destroyed by fire. The 160 ft cable and shock absorber unit were released before ground impact. An operational check of the release hook was normal.