From Smithsonian Magazine:
Thus it was in the remote south of the forest in the summer of 1978. A helicopter sent to find a safe spot to land a party of geologists was skimming the treeline a hundred or so miles from the Mongolian border when it dropped into the thickly wooded valley of an unnamed tributary of the Abakan, a seething ribbon of water rushing through dangerous terrain. The valley walls were narrow, with sides that were close to vertical in places, and the skinny pine and birch trees swaying in the rotors’ downdraft were so thickly clustered that there was no chance of finding a spot to set the aircraft down. But, peering intently through his windscreen in search of a landing place, the pilot saw something that should not have been there. It was a clearing, 6,000 feet up a mountainside, wedged between the pine and larch and scored with what looked like long, dark furrows. The baffled helicopter crew made several passes before reluctantly concluding that this was evidence of human habitation—a garden that, from the size and shape of the clearing, must have been there for a long time.
It was an astounding discovery. The mountain was more than 150 miles from the nearest settlement, in a spot that had never been explored. The Soviet authorities had no records of anyone living in the district.