Nilsson's nomadic hosts present him with yak butter and caterpillar fungus. [Photo by Erik Nilsson and Tseringbum/China Daily]

That is, pliable enough to forge fences of feces that serve as fuel.

They're constantly torn down and rebuilt－to burn and to protect.

Once I'd filled the wheelbarrow, it was time to lead the yaks to the mountaintop pasture. My hosts taught me to whistle to get them to hustle.

Next, it was time to release the sheep.

They gave me a slingshot, which locals jokingly call "Tibetan guns".

Herders fling stones to steer flocks.

I twirled the weapon and hit myself in the head.

Later, I visited a shack behind the nomads' home. The family poured yak milk into a filter atop a sputtering machine with two nozzles. One dribbled out the base for cheese. The other oozed butter.

The family gave me a chunk of yak butter the size of a basketball, wrapped in khata (traditional Tibetan scarves) and six sprigs of caterpillar fungus wrapped in tissue as a parting gift.

Tseringbum explained I can slow-boil a single piece of the parasite with a whole chicken or steep several pieces in the deer-blood liquor he'd given me, for at least a year. (The longer the better.)

The first snow of 2017 fell as I prepared to leave. Winter begins in early August.

I waved to the family.

A marmot I'd seen flash from its burrow when I arrived popped out of its den, as if to say goodbye.

And I bid farewell to the people, the wildlife and the livestock－including the yaks that buck.