Outdoors Magazine

On the Road: Geo-challenge 1

Posted on the 22 October 2014 by Hollis
On the Road:  Geo-challenge 1Where are we?
Plants & Rocks is on vacation.  First destination was an east-west mountain range often described as an anomaly because contemporaneous ranges mostly trend southeast-northwest.  Actually there are several others like it, though not as large.  This one may have been influenced on the north by the Cheyenne Belt -- an east-west suture zone where crust was accreted to ancient North America roughly 1.5 billion years ago.

On the Road:  Geo-challenge 1

Red sedimentary beds on left are Precambrian.  They fooled all three early geological explorers.

The Precambrian core of the range is sedimentary – conglomerate, sandstone, siltstone and shale.  Sediments were deposited in a rift valley when the continent was coming apart, close to where it had been sutured.  It didn’t tear all the way, but was deep enough to accumulate 20,000+ feet of material.
On the Road:  Geo-challenge 1
Something like seven hundred million years later, the east-west mountains rose during a great regional mountain-building event (below).
On the Road:  Geo-challenge 1
Sedimentary strata on the flanks of the uplift were steeply folded, making for great scenery.  Some roads follow strike valleys between spectacular hogbacks.
On the Road:  Geo-challenge 1
The sedimentary rocks are just as wonderful on the south side of the mountains – like the ones below.
On the Road:  Geo-challenge 1
Josie Bassett ranched here at the mouth of the box canyon until she was 89.  “Independent in both action and thought, she lived life on her own terms.”

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