Michael Hiteshew

200 million years ago North America sat about 20 degrees above the equator. The newly born Mid-Atlantic Ridge was breaking Pangea apart, separating Laurentia from Gondwana, and one arm of the rift feature was beginning to propagate through Gondwana, beginning the separation of South America as well.

Western Laurentia was a sea of sand, the remnants of which are still found all across the western USA as massive cliffs of buff colored sandstone, often over 1,000 feet high. The defining features of the Navajo Sandstone, besides its color, are the the large-scale cross-bedding and its tendency to weather across its exposed top surface into domes and rounded forms. The Navajo was one the largest seas of sand dunes ever seen on the planet. The most spectacular exposures of the Navajo are to be seen at Zion National Park where it reaches more than 2,500 feet in thickness. When the Colorado Plateau was uplifted in the Laramide Orogeny in last 45 million years, that created a lot of elevation difference between the uplifted ground surface and sea level, which allowed water to cut deeply through  the rock, exposing it to erosion. If you look at the cross section of the Grand Staircase below, you’ll see that more than a mile of rock has already been eroded from the ground above the Grand Canyon, the Vermillion Cliffs, and the White Cliffs of Navajo.

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