ON THE FINAL MORNING we paddled toward Spruce Park Gorge and the Flathead's biggest rapids. Up until then, the canyon had been friendly, like someone had carved a V in a big cake, a mocha-colored loaf with spruce-green frosting. But now the mouth of the gorge looked ominous, with walls so steep that nothing grew on the loose dirt. As Ken and I caught an eddy, looking down at the sharp granite rising up on both banks, I was a bit nervous. Adam paddled over and produced something silver—a flask of bourbon. "Liquid courage," he said.

Before we launched that morning, Adam and Ken and Nate and I were walking through the woods when Adam revealed something I didn't know. "My dad died at 50, of cancer," he said. "His dad at 50, too, from a heart attack." Adam was only 37, not the age to be brooding about the final end, but I did the math. Thirteen years isn't a whole lot of time.

No one knew what to say, so we just kept walking. Adam changed the subject. He told us about this idea he has for a trailer he wants to build, so his boys can haul their kayaks behind their bikes to the new surf wave in town. It sounded like a fine idea, brimming with optimism, and I didn't want to be the wet blanket who pointed out that the plan was a bit premature: Before hauling their kayaks to the river, the boys will need to learn to paddle, to ride bikes, and to cross the street. I mean, they're two years old.

Just then, without warning, Adam's feet kicked out from under him in the mudflat and, with a nauseating thud, he thumped on his back like a sack of flour.

Oh, shit, I thought. He's dead.

I rushed over and he opened his eyes.

"I'm fine," he said. "I just slipped." We pulled him up. And it hit me then that for all the fretting men do about getting old, about being deskbound or mortgaged or bald, these are just symptoms. The real disease is mortality, and each of us has a terminal case. Those moments glissading down a snowfield in the Chugach or hauling a trailer down Baja's carretera peninsular with windows down and ranchera blasting oom-pah-pah on the stereo, not much on your mind but getting to the next place—you can call that youth, but more accurately it is thinking you will live forever.

There in the eddy we passed around the bourbon, then caught the current and raced downriver. The kayaks and rafts trundled down the canyon, pinging off the walls and each other, submerging in troughs and bursting through the crests.

The gorge only lasted a couple of miles, and as soon as it was over I wanted it to start again. I always want to return to those moments where past and future disappear and the present is as vivid as thunder: A wave crashes and you brace, a rock appears and you dodge it, a hole flips you and you roll back up. Across the water my friends bobbed in their boats like rescue buoys, and I was sure everything would be all right. If that gorge had never flattened out, and the river poured through it forever, we could have paddled on and on, my friends and me; we could have headed downriver, always one more bend ahead, and we would never have to die.