When I visited the Upheaval Dome in 1987, I was sure it was an impact crater. But roadside displays and printed literature from Canyonlands National Park said otherwise. Clearly, they reported, this was collapsed salt dome. Since then German researchers have found evidence, through shocked quartz, of an impact. That now appears to be the prevailing theory. The crater is approximately 5 km in diameter and must be Jurassic in age or younger, given the ages of the rock it hammered. From bottom to top, those rocks are:
- Organ Rock Shale (center of the bulls-eye) and White Rim Sandstone (the pale ring around the center), both elevated in a dome-like shape, are part of the Cutler Formation, which was deposited in the Permian period, which ran from 299 to 251 million years ago. In geologic time, the Permian period was the last of the Paleozoic era. That era ended with a mass extinction — bigger than the one that wiped out the dinosaurs at the end of the Mesozoic era, which began with the Triassic period. The Jurassic and Cretaceous, which followed, are barely represented here.
- Moenkopi Formation, first in the Triassic suite that follows
- Chinle Formation
- Wingate Sandstone
- Kayenta Formation
- Navajo Sandstone, which bridges the Triassic and Jurassic. That’s the pale hard rock providing the top layer in this picture.
Navajo Sandstone also stars in Zion and Capitol Reef National Parks, in Comb Ridge, San Rafael Reef and the Red Rock country overlooking Las Vegas from the west (where it is called Aztec Sandstone). Its cross-bedding strata suggests windblown sand, which is exactly what comprises the rock. The whole formation is the fossilized remains of a Sahara that once covered much of The West. Think of it as a fossil desert within a desert.
So I was flying over the area last week, and got some good shots of the thing, including the one above. There are many more in that series, which stretches from Boston to San Francisco, by way of Newark. I’ll put up other segments soon, I hope.
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