On the Road: Geo-challenge 1

Where 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.

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.Something like seven hundred million years later, the east-west mountains rose during a great regional mountain-building event (below).Sedimentary strata on the flanks of the uplift were steeply folded, making for great scenery.  Some roads follow strike valleys between spectacular hogbacks.The sedimentary rocks are just as wonderful on the south side of the mountains – like the ones below.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.”