Friday, September 12 had been an immense day, from waking up to hoarfrost and a moving conversation to lunching at the “cradle of conservation” to plunging into the awful heart of a latter-day gold rush.

But now we had reached the North Unit of Theodore Roosevelt National Park, where our journey through the Dakotas would conclude.

Immediately, the North Unit felt different from the South Unit, although we were still in the Badlands of the Little Missouri River. Half of this unit is federally designated wilderness. Through most of its course, the Little Missouri flows north. But here in this smaller unit (slightly more than half the size of the South Unit), the landscape is oriented around a great turn in the river as it meanders east. In the South Unit, the river is incidental, flowing through the western section of the Badlands. In the North Unit, the river is the centerpiece, carving a great, tantalizing valley out of bluffs and prairie.

At the Little Missouri in the North Unit, in one very particular way, the continent cleaves itself in half. Here the north bank of the river marks the Central Time Zone, while the south bank marks Mountain Time.

In we drove. Our intention was to select at campsite at Juniper Campground, set up camp, and then take the scenic drive, a one-way road instead of a loop. The end of the road was Oxbow Overlook, where the river makes its elegant turn. That would be a perfect place to catch the sunset. The other reason I wanted to hit the scenic drive that evening was that I had grown tired of being in the Jeep. I wanted the following day, Saturday, our last full day of the trip, to involve no car travel whatsoever. As I put it to Sean: “Tomorrow I want to walk out of camp, have an adventure, and walk back into camp.”

In the eastern part of the North Unit, near the entrance and visitor center, which had already closed for the day, the park road follows the valley floor north of the river.

Shortly we arrived at Juniper Campground, situated near the river in a lovely grove of cottonwoods. We registered and took note of a warning posting that many of the backcountry trails through prairie were overgrown and difficult to follow at this time of year. Only hikers with backcountry experience and way-finding skills should attempt these hikes. The only trail out of the camp that didn’t involve fording the river was one of the trails specifically mentioned in the warning. Next morning it seemed we’d be testing ourselves a bit.

We selected campsite 22, a tent-only site nestled into the edge of the woods. We noticed, to our amusement, that two fellows who camped adjacent to us at the South Unit were also in this campground. In the freezing overnight temperatures back in the South Unit, they had slept in their car. Sean decided that their names were Will and Will’s Friend.

We set up camp for the last time. The site was picturesque, dry, and reasonably secluded.

After everything was situated, we climbed back into the Jeep and headed out toward the sunset.

The park road rose gently out of the valley and into the bluffs. Our first stop was River Bend Overlook, which afforded panoramic southerly views of the Little Missouri.

The shelter at the overlook was built by the Civilian Conservation Corps (CCC) in the 1930s.

We continued on.

The road mostly crossed open prairie to the north with the valley to the south. In the distance, Sean snapped a photo of a bison herd.

Shortly we were at the Oxbow Overlook. The Little Missouri gleamed beneath us.

Video: Brandon Hayes

The setting sun added drama to the landscape.

Then, on the cliffs beneath us, I noticed what could only be a petrified log jutting out of the bentonite. The bentonite, of course, would have been softer than the minerals that substituted the living wood. There it was, clearly, a stone log jutting from stone.

In the distance, the valley floor was haunting, tantalizing, beautiful. There was part of me, at that moment, that wanted to extend the trip and backpack for a week in the North Unit.

But instead, we lingered above the valley, examining lichen, gazing out at the changing tones and shades illuminated by the setting sun.

A couple hundred yards to the west was the park boundary. Beyond it pump jacks and a natural gas flare burning into the dusk.

We climbed into the jeep and headed back to our campsite, stopping on the way to watch a flock of Sharp-Tailed Grouse in the prairie grass.

Soon we were in our campsite, warming ourselves against a small, but lively fire, drinking wine out of tin cups. And then to bed.