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TIL the Grand Canyon's Bright Angel Shale layer used to be a lot thicker
I was watching a documentary and they showed how that shale layer was over 500 feet thick 300 million years ago, but now it's only about 100 feet in most places. The big change happened because of erosion from the Colorado River cutting down over the last 5 or 6 million years. It's wild to think how much rock just washed away to make the canyon we see now. Has anyone else seen a spot where you can really see how much a single rock layer has been worn down?
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sullivan.nina6d ago
My buddy went hiking out in Utah last year and showed me photos of this cliff face where you could see a huge band of sandstone just... gone. Like, the layer above was hanging there with a gap under it, and you could follow the line of where it used to be for miles. He said the park ranger called it a "weathering pit" that collapsed and took a whole chunk of geologic history with it. Made me feel kinda small, lol, thinking about how much solid stone just falls apart over time. Your post about the shale totally reminds me of that.
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park.iris6d ago
That's wild, @sullivan.nina. I've seen smaller undercuts in sandstone, but a gap that goes on for miles is hard to picture. Do you know what kind of rock the missing layer was, like was it a softer sandstone that just turned to sand and washed out?
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