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Where did so much sand come from? Much of it, apparently, from the Appalachian Mountains far to the east. Geologist Jeffrey Rahl and his colleagues found clues to its origin in tiny crystals of zircon embedded in the sandstone. Radioisotopes in Navajo zircons match those in zircons from the Appalachians, which were once as high as the Alps.

Presumably sand eroded from these peaks was borne westward by rivers, then swept by winds into a fantastic sand pile. At the time, the plateau part of North America is reckoned to have been somewhere near central Mexico, chugging north toward its present site at a few millimeters a year.

There's little evidence of life in the Navajo sandstone, but around 160 million years ago in the late Jurassic period, a new landscape began to develop—a panorama of forests, rivers, swamps, and inland seas, in which flourished dinosaurs, crocodiles, giant seagoing lizards, and huge sharks. Fossils of these monsters speckle the Morrison, Cedar Mountain, Dakota, Mancos, and Kaiparowits formations, built of sediments such as mud and carbonates.

Beside a road in Utah's Grand Staircase–Escalante National Monument, a gulch reveals the transition from the dry sands to the watery late Jurassic and Cretaceous environments in which life thrived. Atop the sandstone is a coal seam, the relic of a swamp. And above that a strip of hard-packed sand mixed with mud, the shore of an advancing sea. Next: a fossilized oyster bed—replete with fossil pearls, people say—laid down when the shifting shores had created a bay.

Compared to the geologic record, the recent jottings of humankind in the plateau country seem faint indeed. Some of the bravest sagas, just a century or so ago, left hardly a trace. There was, for example, the party of Mormons, some 250 men, women, and children, who pushed into southeastern Utah in the snowy winter of 1879-1880, building a road along high ridges as they went.

Above the Colorado River at Glen Canyon they used ropes and chains to lower their 83 wagons down a skinny crevice they named Hole-in-the-Rock. Then, 1,800 feet (550 meters) below, they had to get their wagons and cattle across the icy river—300 feet (91 meters) wide there—and surmount a high cliff on the far side. They lost not a wagon in that crossing, and during the almost six-month odyssey their roster increased by three newborn babies.

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