on a local pleasure flight from a private facility at Redfern Lake, BC. As the pilot attempted a landing at approximately 7800 feet ASL near the edge of a cirque, the aircraft encountered descending air on final. The pilot elected to continue the approach and increased the collective to maintain the sight picture. The pilot then noticed the low rotor warning with the rotor RPM decreasing rapidly toward 70%. The aircraft landed hard and rolled over several times down the slope. The pilot and the two passengers evacuated the aircraft with no injuries. There was no post impact fire; however the aircraft sustained substantial damage.