Читать книгу One Best Hike: Grand Canyon. Everything You Need to Know to Successfully Hike from the Rim to the River—and Back онлайн

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Initial breakup of Pangaea, 250 million to 145 million years ago: The Grand Canyon region was an arid terrestrial environment throughout this time. The 4000 feet of sediment, mostly desert sand, deposited atop the Paleozoic strata have since eroded. No sediments from this time period, the Mesozoic, survive in the Grand Canyon, but they are visible farther north on the Colorado Plateau.

Subduction of the Pacific Plate begins, 145 million to 70 million years ago: During this period, Pangaea continued to breakup, causing North America to be pushed westward, and the Pacific Plate to begin subducting beneath it. This new subduction zone created the beginnings of California’s Sierra Nevada and thickened the continental crust west of the Grand Canyon, causing the Colorado Plateau to be depressed. An internal sea, the Mancos Sea, flooded the central parts of North America, including much of the Colorado Plateau. The water retreated toward the end of this period. Around 70 million years ago, the strata that are now on the rim of the Grand Canyon were still at sea level.