JUST NOW JONATHAN'S BEHAVIOR is taking on a certain Brigham Young quality. He's a zealot about this place, striding in front, the trail visible only to him. Pato comes next, Marlboro in teeth, machete in hand. Our packs are loaded, the terrain's getting rougher, Scott's battling a stomach flu that also nailed Jonathan and Mary Ann in Bertrand. We descend into giddy punchiness as we imagine recommending this slog to friends. In two days we've tramped through marshes and meadows and waited out the rain in the cabin of a gaucho named Muncho, passing a gourd of yerba mate, South America's ubiquitous herbal tea, around the woodstove beneath the socks, underwear, and leg of lamb that hung drying over the fire. We've crossed a swinging bridge that Toby and Jonathan jury-rigged out of baling wire and dodged Muncho's mangy, charging ram.

Now there's the river. Crossing each bend of the Río Soler is a frontier proposition, Hector pacing his pony back and forth on wide gravel beaches as Jonathan calls out crisp questions in Spanish until they settle upon a place to ford. The horses are almost swimming, the larger ones breaking the current for the smaller ones. Nate's pony goes in up to his withers.

Seventeen miles up-valley, a raging creek flows in clear to join the silty Soler, an unnamed peak filling the V between the two streams. This is Palomar. There's a single one-room puesto, an outpost for a lone gaucho, and a meadow, a simple corral, and a ring of fruit trees. "Don't step on the trout," Jonathan calls as his horse splashes across.

Palomar is where the adventure heats up. Scott is already pale beneath his sunburn, and at breakfast Jonathan drops a kettle of boiling water on Jose's foot, skinning a four-inch patch of his ankle. Anyone else would have taken a horse back out, but Jose limps on, fueled by Percocet and an impeccable mix of English and Spanish profanities.

It's snowing the next day when we reach the Neff Glacier. The thing is massive, 200 yards thick in places, four miles wide. The near side is piled with loess, glacier scour embedded onto the ice. Beyond that, whiteness. Jonathan raises a fist—"Yeah! Power! Place!"—before offering up a lesson on the alarming shrinkage of Patagonia's icefields, two of whose glaciers, the Neff and the Soler, he has measured as receding at 25 and 100 feet a year, respectively.

Soon we're in a full-on whiteout, not the best weather for crossing crevasses unroped. "Here's the deal," Jonathan says as we strap on crampons. "If we get out there and there's three feet of snow, we turn back. If a giant gorilla falls from the sky, we turn back." We start walking at 10:30; halfway across, the sun comes out, shining down on a spectacular world of ice. Life becomes the crunch of crampons, blue ice, whiteout, sun, rain, more sun, snow. It takes seven hours.

The next afternoon we hit what's been billed as "the burly talus slope," a half-mile of boulders teetering on some ever-shifting angle of repose, the slope dropping straight into Lago Cachet Dos, its navy water crisply accented with small white icebergs. "Don't slip," Jonathan says helpfully, "or you'll die."

Exhilaration turns to fear. I watch Pete ride a slide into the lake up to his thigh, and the more rocks I dislodge, the more nervous and angry I get at Jonathan's little vision of a "trail." This guy's a nut, I think; this place isn't ready. We're crossing glaciers unroped, skidding down talus, clawing up mountainsides? Maturely, I glare at the back of his peppy, bereted head and blink back tears.

My meltdown, naturally, is Jonathan's favorite part. For a man who views his profession—"adventure guide"—as an oxymoron, this is the way it should be.

That night we camp on a rock outcrop with a front-row seat on the Colonia Glacier, less than a mile across Lago Cachet Dos. A 270-degree panorama of peaks surround us, lit by the rising full moon. It's the single most stunning campsite any of us has ever seen, and the talus is forgotten.

We're fried, of course. Even Jonathan confesses to being overwhelmed. It's all getting very big. He has to build the yurts, stabilize a path across the talus slope, provide ropes for crossing the glacier. The huts themselves will come slowly—one in 2006, two in 2007, and so on. But chaos is business as usual down here: Patagonia doesn't attract executives with thought-out business plans. It attracts grown-up 12-year-olds with grubby dumpster maps.

"The trail needs to be hard at first," Jonathan says. "I don't think that the millions of Americans who do adventure travel would necessarily want it to be as brutal as it is now, but there will be a lot of people who will come in the next six years who will be just thrilled to death."

And until then? What about those who like their adventure soft-boiled? "So they'll go somewhere on more developed treks," he says. "It's our time now."

The next two days unfold in an unreal parade: glacier, peak, old-growth forest, glacier, lake, peak. We emerge onto Lago Colonia's wide beach to see Hector, who's come the long way around, waiting with the fishing boat. Jonathan's going nuts: It's been more than a decade since Scott first told him about this valley, and now—wow! yeah!—this. Leaning back in the bow, virgin mountains rising across the lake behind him, Pato lights a Marlboro Red and passes it down to Jonathan. They've done it.

An hour later we're at Sol de Mayo. Lalo's paradise is just that: two neat houses surrounded by apple trees and sheep. Mary Ann has walked up the Valle Colonia with Hector to meet us, and there's bread baking in the woodstove.

Late the next afternoon, with only one day's walk out to the Río Baker, I wake up from a nap in Lalo's pasture. The Río Claro cuts two feet from the corral, rushing past the new wood-burning showers and composting outhouse, past the fogón—the smokehouse, with its sheep leg drying—past Jonathan and Mary Ann's cabin, once Lalo's, past Lalo's new house, with its new running water and faded poster: LA VERDAS ES EN LA NATURALEZA. In nature lies truth.

I wander over to the barn. Inside hang sheepskins, saddlebags, the goatskin that Hector and Lalo skinned yesterday to make chaps, a shopping bag reading I LOVE YOU. Hector and Lalo are shoeing a bay horse; Lalo's sheepdog naps between its legs. I start thinking about what Cado Avenali told me back in Coyhaique.

"You look around the world," Cado said, "and see what's going on, and you realize that there isn't anywhere else. This is the place. The others are places you go to look at. Here you can live."

It's easy to romanticize Patagonia. And you'd be a fool to think that, as more gringos arrive, there won't be plenty of outsider arrogance. But so far idealism is overcoming the growing pains, and it's nice to think that visitors can have some place in holding back a dam. As John Hauf put it, "That's the beauty of Patagonia: It allows you to dream of a broader place where anything is possible."

And so we dream of a great, big do-over at the bottom of the world. Scott's talked about moving his young family here for a few years; Toby's hiding out as long as he can from Iraq. As for me, I'm thinking of a little farm on the wide, blue Baker, just where the Río Neff flows in.

I won't be a bad gringo, I tell myself. I won't ruin anything. I'll do it right.