Rambling in a rubbly, lunar, black-and-tan landscape where nothing grows but saltbush. Water-scoured sediments, here and there a hunk of dinosaur bone, and hundreds of stones so  polished they might have been tipped from a rock tumbler. John, the geologist, says they’re gastroliths: dinosaur gizzard stones.

“Swallowed by dinosaurs as they traveled their migration routes,” he said. “Maybe hundreds of miles long. None is bigger than a grapefruit; if they were the result of normal deposition they’d be more varied in size, with no upper limit. And they’re all exotics, not from any source near here.”

“Then where are they from?”

He said, “The mountain range they came from has long since worn away.”

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