It’s an impression that only intensified when I had my first look at them up close a half-hour after my friend Aimee and I had entered the park. A few grazing near the road raised their grand heads to watch us as we passed in Aimee’s Honda: their faces, primordial; their dark eyes, indecipherable; their ability to flatten our little car if they felt like it, absolute.

To see them so close felt like a lucky stroke. Millions once roamed the continent, but by 1900 their numbers had dwindled to the low hundreds in the wild. Because of conservationists — indeed, because of the existence of the national parks — the bison had persevered. To catch a glimpse of them on the prairie was to bear witness to their survival.

The sun was setting by the time we reached the Sage Creek campground, a waterless patch near the park’s designated wilderness area at the end of a gravel road. All around us the world was magic, the way the world is always magic at sunset in wild places, but it seemed especially so that night, the grasslands giving way to the ancient hills and rocky buttes beyond. We pitched our tent in the fading light.

When I stepped out of our tent the next morning, there was a bison grazing about 50 feet away. He lifted his head in my direction and — for a reason I do not know except to say I have always been friendly to a fault — I said, in a tone altogether too cheery, “Good morning, Mr. Buffalo.”