Dacit-towers-in-the-Oak-Flat-of-Arizona's-Devil's-Canyon

And Then They Jumped

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Going solo on his bike, Mark Stephens explores a lost route into central Arizona’s Devil’s Canyon and its legends, before it’s too late.

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Light a match and toss it into a gallon of gasoline and you’ll get an idea of how hot it is today. I won’t be escaping anytime soon, either. Maneuvering my bike on this rocky road’s a total bitch, and I’ve bit off more than I can chew. For some inexplicable reason, I’m thinking about the explosions and erosion that put these rocks here. Explosions and erosion: what else is there to think about anyway while riding solo on a bike?

Another question. Ever heard of the Laramide Orogeny? Rock climbers, hikers, mountain bikers, Jeep-trail nuts, and zany outdoor folk who enjoy the mountains and canyons of the Southwestern U.S. owe serious homage to the Laramide Orogeny.

I’ll explain. This is the geologic event that lasted approximately 50 million years and effectively built the mountains, valleys, and canyons of the western portion of North America. If it hadn’t been for ol’ Laramide, there wouldn’t be a certain heart-stirring

chill to the word “west” and human history here would be drastically different. Because of Laramide, we westerners go outside . . . to celebrate life, if you will.

Hone in on what would be modern day central Arizona, and area known as Oak Flat, 20 million years after Laramide. Right  here under the ground there’s a giant magma chamber cooling down and parts of it are beginning to solidify. But gasses from the magma are getting trapped between the newly formed solid sections . . . and pressure is building. Intense pressure. And it keeps on building for, oh I don’t know, maybe another million years. Who knows? But over the course of just a couple of days the earth’s crust gives way and releases a gigantic plume of ash – like a couple hundred cubic miles worth – along with an avalanche of molten rock. Again and again, over and over. Each new layer of magma and ash lands before the previous layer completely cools. The intensity, weight, and concentration of it all essentially welds the layers together. Mother Nature, after all, is a welder.

Eventually the eruptions end. The remaining dacite foundation cools, traps more gasses which form pockets in the solid material, and an ash layer cools faster and produces contraction – the contraction causes millions upon millions of vertical fissures to form in the rock.

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