The pilot reported that he was landing the helicopter in a bowl-shaped meadow surrounded by mountains and trees. While circling the landing zone to determine the surface winds and descending, about 20 feet above ground level, the helicopter encountered a wind gust. The low rotor horn sounded and the pilot regained rpm, but another wind gust from behind again resulted in a loss of rotor rpm. The pilot said he was too low to recover, so he performed a run-on landing. The helicopter struck an earthen berm and rolled onto its left side, which resulted in substantial damage to the fuselage and tail boom. The elevation at the accident site was 8,411 feet; the density altitude was calculated to have been 10,059 feet. The pilot reported no preimpact mechanical malfunctions or failures with the helicopter that would have precluded normal operation.