It took us across Montana's windswept prairie where a thin coat of snow clung to the threshers hulking in the hayfields, along the brick-lined Main Street of downtown Great Falls, where the town's copper smelter is long since gone and now the neon signs of the bars and the drugstore flicker on empty sidewalks, and then through the high antelope plains where opening day found trios of hunters carting their prey through the knee grass to big pickups parked on the shoulder. This road could get under a person's skin.

We were driving the length of U.S. Route 89, connecting strands of two-lane blacktop through Montana, Wyoming, Idaho, Utah, and Arizona, from Glacier National Park along the Canadian line all the way to the dusty Mexican border crossing of Nogales. The idea was to ride the crest of changing leaves southward, but as we set off, a cold snap bore down into Montana from the north, so instead of surfing autumn we were getting blown south by winter.

In Glacier National Park the aspen leaves had dropped and the lodges and gas stations were boarded shut for winter. We had missed tourist season, and as we cooked dinner on a campstove in the freezing darkness of an abandoned campground, I felt a little bleak. When we awoke before light, I heard photographer Jeff Pflueger, my longtime traveling companion, twitching in his summer-grade sleeping bag. "No reason to lie here getting cold," he said. We leaped up and, blowing clouds of warm breath into the beams of our headlamps, boiled some water for coffee, shoved down some Pop-Tarts, and headed up the trail to Iceberg Lake.

And that's when I realized that this was, in fact, the right time to be in Glacier. No one was there. We switchbacked up the valley while mist rose from its floor, and as the black distance turned gray, the jagged skyline revealed itself. We raced up through the alder brush, hopping over creeks as the snowflakes danced around us, charging forward with the adrenaline that comes from having a...