Thursday, June 3, 2010

Mega road trip - Day 3

Spending the night in Goodland, KS, a few miles from the CO border.  Kansas was a LONG drive but at least there are a few things of geological interest. 

Central to western Kansas was Post Rock Country.  Here, the lack of trees and need to fence in cattle led the early settlers of the area to create fence posts out of the abundant limestone in the area.  Below is an image from the KS Geological Survey showing an in situ limestone layer and a stone fence post.

Each post weighed between 250-450 pounds and was carved out by by hand.  There are thousands of miles of stone fence posts in this part of the state!  The rock, called Fencepost Limestone (naturally) is, to geologists, the top part of the Greenhorn Limestone Formation which was formed around 95 million years ago (the Cretaceous Period) in the Western Interior Seaway.  As a matter of fact, some of the limestone fenceposts contain visible fossils of clams and ammonites (squid-like animals).

The Western Interior Seaway once ran up the middle part of North America and deposited marine rocks in places like western Kansas.  Visit the Oceans of Kansas website to learn more about this (the web site is poorly designed but does contain a ton of information when you scroll down). 

Another rock unit deposited besides the Fencepost Limestone was the Niobrara Chalk Formation.  This unit is about 85 million years old (10 million years younger than the Fencepost Limestone) and also contains marine fossils including sharks and mosasaurs (crocodile-like predators reaching 30+ feet in length!) which were swimming in the Western Interion Seaway when T. rex was stalking the landscape.

We did make a side trip about 20 miles south of Oakley, KS to Monument Rocks, an exposure of the Smoky Hill Member of the Niobrara Chalk.  You drive through miles and miles of flat prairie, turn off on a dirt road for 6 miles, and then come upon the following:

A mass of white chalky rocks jutting up from the flat landscape.  Imagine the chalk covering the entire landscape and then imagine it as the bottom of a shallow sea!  You can drive right up to them and walk around and inspect the rocks.

They are clearly chalk deposits and contain a lot of fragmentary fossil material (shells mostly).  I didn't find any mosasaurs!  I'm convinced, however, that if I had some time to spend here I could find some interesting stuff (it's not a collecting site, however).

My wife and kids give some idea of the scale of the outcrops.  Erosion has carved them into interesting shapes.  If you're ever driving by on I-70, it's worth the hour or so side trip to visit.

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