“Ripples. Kind of frozen here, in the loess. Like small dunes, I guess. The dunes are stratified. It looks as if a river has dried out here.” He stalked on over the rock. “I have pits in the rock surface. Circular, a few inches deep, width from a foot wide upward. Scallop pits, I think.” Gouged out by pebbles, carried by turbulence… “The whole place is kind of like a river bottom,” he said. “Yeah. You basically have the topography of a dried-out river bottom — but magnified. Channels and bars and islands. All shaped by flowing water on a massive scale…”

He looked around with a new excitement, seeing the geology with new eyes, with Natalie York’s eyes: the deep-carved, breached channels, the huge deposits of loess, the carved-out islands. “Christ. Is that it, Natalie? Is that what you’ve brought us out here to see? Was all of this region formed by a flood?”

“You’re speculating again, Stone.”

“Oh, come on, York.”

“Okay. You’re right, Phil. At least, that’s the favored hypothesis.”

Bleeker gave up on the half-assembled CELSS, and came to stand close to Stone. “What is?”

York said, “In the Late Pleistocene — maybe twenty thousand years ago — much of Idaho and west Montana was covered by an immense lake. Called Missoula. Thousands of square miles of it. The lake was contained by an ice dam. The dam eventually burst, and released a catastrophic flood that swept over this area. Tens of millions of cubic yards per second, maybe a thousand times as much as the Amazon’s discharge rate—”

“Jesus,” Stone said.

“Yeah. The existing streamways couldn’t cope with the sudden volume, so they burst; the valleys were widened and deepened, and interconnecting channels were cut — all the way into the bedrock — in hundreds of places. Thousands of square miles were swept clean of the superficial structures, right down to the basalt bedrock, and another thousand square miles were buried in river-bottom debris.

“We’re left with hundreds of cataract ledges, basins, and canyons eroded into the bedrock, isolated buttes and uplands, gravel bars thirty or forty yards high.

“This is the scabland, Phil. There are only a handful of areas on Earth which show the effects of large-scale, catastrophic flooding so well.”

Bleeker pushed back his Snoopy hat and scratched his blond head. “It’s fascinating, Natalie. But I don’t see what it has to do with us.”

“Okay. Phil, I’ve given you another pack of photographs. In the left side-pocket of Adam’s pack.”

Stone dug into Bleeker’s pocket and pulled out a plastic packet of black-and-white photographs. He leafed through them quickly, showing them to Bleeker.