The helicopter had been dispatched to pickup and transport two ground crew members to a new location. The pilot positioned the helicopter with the front skids into up sloping terrain when the main rotor blades impacted a large boulder. The helicopter pitched back, rolled onto its right side, and slid down the hill before it came to a rest. During the accident sequence, the helicopter sustained substantial damage to the fuselage. The pilot reported no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation.