Almost all of them were “parkies,” as one man eventually put it. They were giving a going-away party for one of their supervisors, who was leaving for a new detail at a park near San Diego. Someone pointed him out: an older, smiley, muscular man in a T-shirt that said, “Yard Sale.” They eventually sang “Happy Birthday” to someone, too — a younger guy in a camouflage hat, holding a generous glass of red wine lazily aloft and squinting. At one point, another man dropped a pint, and it shattered. The entire room shouted and applauded. Then Yard Sale graciously, dutifully appeared with a broom and — maybe, I wanted to imagine, just to leave his troops with one final image of how a true leader behaved — swept up the glass.

Off in a corner, I struck up a conversation with Thor Riksheim, a tree-size Park Service veteran with an impressive mustache. Riksheim directs historical preservation at Sequoia. He had recently restored the only Kaweah Colony building remaining in the park, a remote cabin that the government calls, a little ruthlessly, Squatter’s Cabin. The colony had been conspicuously written out of the official story of Sequoia National Park, and its road has long since reverted to a trail. But Riksheim spoke affectionately of the cabin, which he called “Squatty’s,” and the colonists, too. (He also called the General Sherman Tree “Sherm,” as if they’d gone to high school together.) Right away, I liked him immensely. It was clear his connection to the trees was deep and singular. He was currently living in another historic building he had restored in the heart of the Giant Forest — in the shadow of the famed Sentinel Tree, a cluster known as the Bachelor and the Three Graces and other sequoias. It was touching how privileged he seemed to feel, how proud. “I’m Giant Forest, population 1,” he told me.

To a human being, a 2,000-year-old sequoia seems immortal. But I noticed that people like Riksheim who have lived closely with the trees aren’t prone to mistaking their longevity and resilience for indestructibility. To know sequoias means being cognizant of their weaknesses, understanding them as provisional objects in some vaster, slower-moving natural flux. In fact, there’s a prominent exhibit at the park’s Giant Forest Museum chronicling how the government nearly undid the trees’ entire ecosystem through misunderstandings and mismanagement. By the 1930s, the Park Service had constructed a small resort town for tourists in the center of Giant Forest. There were restaurants, cabins, a gas station, a hotel and a grocery store — nearly 300 buildings, erected over the sensitive and shallow root systems of the sequoias, which never reach more than about six feet below the surface. The Park Service vigilantly fought back the beginnings of forest fires; this seemed wise, fire being a reckless and destructive force, but it actually kept the sequoias from reproducing. (It was not yet understood that, among other ecological benefits, heat from wildfires opens the trees’ cones and allows them to spread their seeds.)

All of this was gradually corrected. Then droughts started intensifying. The climate was shifting. The Park Service is now contemplating “assisted migration” of the sequoias: manually planting them farther north to keep pace with climate change. But of course, Tweed, told me, it’s now conceivable that the Trump administration might not allow climate change even to be mentioned at national parks’ visitor centers. Or that the administration, which picked a Twitter fight with the National Park Service on Day 1, might decide to privatize management of those lands. Who knows, Tweed said: “The worries are deep and profound.”

That is, there is another time scale on which the trees are vulnerable, on which the trees are small and come and go as we do: sprouting, growing up, suffering through storms, receiving scars, losing limbs, before they finally drop. Every so often, the imperceptible turbulence and instability in which the trees exist does upend them. Apparently, the first thing you hear when one is falling is a blistering and percussive crackle — the roots snapping, one at a time, underground. It may be far less likely, at any given moment, that one of the sequoias in the park will keel over than that one of the tourists will, but it could happen. It must happen, every now and again. Earlier this year, a famous sequoia with a road tunneled through its base, known as the Pioneer Cabin Tree, farther north, near Sacramento, toppled over in a storm. At the Giant Forest Museum, I saw photos of another one that flattened a parked Jeep in August 2003.

I don’t know why, but I could not stop thinking about this while trundling around the park that weekend: I kept privately picturing them cracking and crashing down. It was a tremendously upsetting image, but still never felt possible enough to scare me.

Late one afternoon, I lay down in the snow at the base of one for a while, watching as the fog poured in through its crown, and I remembered how untroubled Riksheim sounded at the bar the previous evening when, lowering his voice, he mentioned that there was a particular sequoia near his house that he was keeping an eye on. He could wake up dead tomorrow, he said. “It’s just that flying, fickle finger of Fate. Every once in a while, it’s going to point at you.” Then he fluttered his long, bony index finger through the air and lowered it with a sudden whoosh. Out of nowhere: crash. And I realized that his experience of it — a feeling of forsakenness, of arbitrary cruelty — would be essentially the same as the tree’s.

Two days later, I was snowshoeing around alone when I discovered I was standing in front of the same sequoia I had lain under. There, in the sloping snow at its roots, I saw my imprint. My back and legs and arms were joined into a wispy column, with the perfectly ovular hood of my parka rounding off the top. It looked like a snow angel, but also like a mummy — an image of both levity and dolefulness, neither all good nor all bad. I took a picture of it: what little of myself was left after I’d gone. The figure looked smaller and more delicate than I thought it should, but the Giant Forest was so quiet that I couldn’t imagine who else it could be.