Remnants of a Shallow Sea: A Visit to Monument Rocks in Kansas

In remote western Kansas, groups of rock pillars stand like a natural Stonehenge over the grassy plains.  One such group of these pillars south of Oakley is named Monument Rocks.  Returning from our Wyoming and Colorado adventure, we stopped overnight in Scott City, Kansas just south of this interesting rock formation. The following morning we made our way along many miles of the yellow brick road – uh, dusty gravel road –  to Monument Rocks.

Below I share with you what we saw at this rock formation and tell you a bit about its origins.

Above you see our first sighting of Monument rocks looking north.

This picture was taken from the southeast looking northwest.  The mounds in the front are remnants of what was surely several additional pillars of rock in the past.

I am looking west in the picture.  One of my sons is to the right of the large pillars for scale.

This is the view looking southwest after driving past Monument Rocks on our way to Oakley.

What is the origin of the Monument Rocks? 

The monuments are the products of erosion of chalk that once covered the entire region.  Chalk is a soft limestone and is produced as the result of the death of countless small calcium-shelled microscopic organisms  (Formaniferans – see my post: Forams and Diatoms: Testing the Young Earth Flood Geology Hypothesis) which fell onto the shallow sea floor.  As the shells accumulate it forms a soft bed of material that serves as the substrate for other organisms such as a variety of filter feeding clams.  The accumulating substrate eventually would engulf anything that came to rest of the sea floor including remains of clams and oysters but also sharks teeth, and remains of fish and even pterosaurs.

This accumulation of tiny shells must have continued for long periods of time resulting in hundreds of feet of limestone chalk.  This accumulation of layers of sea bed material is thought to have occurred about 80 million years ago when this entire regions was an open shallow ocean stretching from Mexico up into Canada that split the continent into two land masses.

Later, the uplift of this region by tectonic forces lifted this rock to its current elevations and it has since eroded leaving these 50-70 foot-tall pillars as a testimony of a past shallow sea and the former height of the land surface in this area more recently.

These chalk/limestone pillars are essentially 100% fossils.  The microscopic organisms erode fairly easily but the large fossils embedded in that matrix of microscopic shells are more resistant to erosion and are clearly visible though not always easily identifiable.

Above I am pointing to the eroding remains of what was a very large shell.  This is giant clam shell (Platyceramus platinus). Some individuals of this extinct species were the largest that ever existed, growing to more than 10 feet in diameter.  The ones in Kansas at Monument Rocks are several feet in diameter with some as much as 4 feet.

As we walked around there were hundreds of these shells in various stages of erosion.  It may not be an exaggeration to say that every hard structure that erodes out of the soft chalk is a fossil of some organisms that lived in this shallow sea in the past. The ground was littered with pieces of broken fossilized shell fragments (see images below).  Most of the large shells also had small fossils shells attached to their surface. These are small oysters that would have used the large shells as a substrate in the shallow sea where no other solid objects would have been available.

These chalk deposits are famous for the more unusual fossils found in them.  These include sea reptiles such as mosasaurs and plesiosaurs.  It also preserved some bony fish and even some pterosaurs (flying reptiles).   All of these preserved fossils including even the tiny microorganisms that make up the bulk of the chalk are extinct today.  They preserve a unique ecology representing a time in the distant past. Their preservation is the result their being part of a stable calm sea over a long period of time.

Our time was limited at this location so I wasn’t able to do a thorough search of the cliff walls and surrounding area. I had hoped to find some sharks teeth or fossilized clam pearls but was unsuccessful.   We had to be content with seeing clam and oyster shells and a few other odds and ends that I have yet to identify.

The tip of my shoe provides scale for the size of the giant clam shell (Platyceramus platinus) that is eroding out of the chalk. The top of the shell is covered with small fossil oyster shells (Pseudoperna congesta)

The edge of a giant clam fossil is visible.  Smaller oyster shells are abundant.
The small “rocks” in this picture are all broken fragments of giant clam shells. These litter the ground everywhere you walk around the Monument Rocks.

This is a close-up of the clam shell fragments. The crystalline columns of the fossilized shell material are clearly visible.   Some of these shell fragments are up to an inch thick.

The edge of a fossil clam shell sticks out of the side of a small hill. It is about 1/2 inch in thickness.

This is a picture of the side of one of the “monuments.” There are several giant clam shells visible.

Another vertical section of the base of the monuments.  Hundreds of large clam shells are found in horizontal layers. Thousands of smaller clam and oyster shells are seen throughout the column.

I’m not sure what this orange structure is but it is very likely a fossil or a trace fossil.

There are four eggs in this picture. These are NOT fossils.  Rather they are eggs of a killdeer bird in a nest made in a pile of fossil clam shell fragments.  I didn’t notice the eggs as I was searching for fossils rather my youngest daughter pointed them out to me.  The cryptic coloration is great. If you look at the full-sized image you will see that the eggs also have small flecks of red coloration.  I have increased the color saturation to accentuate the surroundings but if you were standing 20 feet way it would be very hard to pick these eggs out.  The killdeer looks to lay its eggs is nearly barren areas and it uses color of its eggs to protect them from predators. But the birds have a second strategy to help protect these eggs and we witnessed that strategy as well (see below).
As I tuned my attention to the eggs to take pictures I heard quite a commotion.  I looked up to see a bird obviously yelling at me and floundering around on the ground.  The bird is pretending to have a broken wing to draw attention away from her eggs. This was the best picture I could get of the wild dance it was doing.

I took this picture of myself just before leaving for the long drive to Kansas City.

Standing next to one of the “windows” in the towering monuments.

Turkey vultures keep an eye on us as we head north.  Here 8 vultures sit on fence posts.  I counted 15 vultures in the area. I converted this image to black and white. There was something that made me think of the opening scenes of the Wizard of Oz as we drove through this very remote portion of the western Kansas.

If you have a chance to visit I would just add that if it rains be very careful on the roads.  When the chalk gets wet it feels like driving on an icy road.  On our 6000 mile trip the most treacherous driving was on the wet back roads of western Kansas.

Another place to visit not far from the Monument Rocks and Castle Rock is the Fick Fossil and History Museum in Oakley.  There are some awesome fossils housed here from the region and some really interesting information about the history of humans in western Kansas.