Let’s get excited about rocks!

Look down and you'll see why rocks are such a big deal in the Flint Hills.

Well, maybe excited is a bit strong. I mean okay, maybe some geologists will feel their pulse quicken and breath shorten at the sight of chunks of igneous rocks. Most of us, however, just think of a rock as something to get out of the yard before our lawnmower launches it through the picture window.

We’re talking about the Flint Hills, however, so one of the first things we should discuss is rocks. The next time you drive around the region and look inside a flint hill – and every time you drive along a road-cut that lops off a part of a hill, you get a peek inside – you’ll get a glimpse at the importance of rocks. Another way to grasp the importance of rocks is to take a hike over a hill and look down at your feet. Rocks fill the inside and cover the outside of the of the hills. It’s an obvious statement, so obvious I hesitate to say it, but without rocks, there are no Flint Hills.

One of the things that attracts me to the hills is their unique look. There is something unmistakable about a flint hill. From its flat top, a gentle curve at the edge leads down to a stair-step shaped slope. There’s something appealing about all those curves. And when a row of those curves are lined up along the edge of a valley, like waves rolling onto the beach, the view always makes me stop and stare, even while I’m driving. Okay, maybe I’d better pay more attention to the road when I’m behind the wheel – safety, and all that – but the views of grass-covered hills around here always tug at my eyes.

There's something unique about the curves of a Flint Hills

The thing is, it’s the rocks that are responsible for those alluring curves, because the hills are formed in rock layers. Layers of limestone and shale were laid down at the bottom of ancient waters, sort of like a giant layer cake, except the layers alternate between limestone and shale instead of chocolate frosting and cake. What’s important here is limestone and shale weather and erode away differently. Limestone is porous and full of cracks, so water will run through the stone, but the rock will remain relatively hard and will break up into big chunks. Shale, however, is a compact, small-grained mudstone. Water won’t run through shale. (You can read more technical details at the Flint Hills’ Geofacts page from the Kansas Geological Survey or at the geology page of the Tallgrass Prairie National Preserve)

There’s something else about the limestone layers that helped create the Flint Hills’ “look.” It’s the flint that made the Flint Hills famous. (Okay, I’m being obvious again.) The flint, which is very hard, is found in the limestone. Each layer of limestone is different, however; some layers contain lots of flint and some have very little. The presence of lots of flint means that layer of limestone won’t erode away as fast as the shale layers on top and below it, creating a slope that resembles stair steps. So you can say the hardness of the flint has created the softness and curviness of the Flint Hills’ look.

That brings us to a point of irony. We call them the Flint Hills, but those pumped-up geologists tell us there isn’t actually any flint in these hills. Actually, they tell us, it’s chert. But, the “Chert Hills” doesn’t really have the same ring to it. And think how much it would cost to change the letterhead and business cards if we changed the name. Anyhow, chert is really just a low-grade type of flint, so I think we’re still good.

What all this shows is the uniqueness of the Flint Hills. The limestone layers here in this part of Kansas are unlike any in the country. The amount of flint – okay, chert if you’re a perfectionist – in the hills, the quality of the limestone, and the weathering factors of the shale all work together to create a unique geological place. In another post someday, we can discuss how these rocks are from the permian geological period and how important that is, but this is enough excitement for one post.

Okay, maybe you aren’t excited about rocks yet, but I hope you are at least a little interested. The next time you follow the curves of the Flint Hills, think about rocks.