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Rock Mystery Solved in Southwestern Kansas; Thanks to KGS

Geologists with the Kansas Geological Survey believe the Point of Rocks outcropping in southwest Kansas dates back to the Permian age, about 245 million years ago. (Photo by KGS)

The Kansas Geological Survey has been grappling with a century-old geologic mystery in southwest Kansas. Commentator Rex Buchanan says the experts now think they've cracked the code.

Commentator Rex Buchanan is the interim director of the Kansas Geological Survey at the University of Kansas and a regular contributor to Kansas Public Radio. 


Production assistance for this commentary was provided by KPR News Intern Austin Fitts, a graduate of the University of Kansas.


Out in the far corner of southwestern Kansas is Point of Rocks, a flat-topped hill overlooking the Cimarron River, a landmark on the old Santa Fe Trail. Wagon ruts are still visible nearby.

Point of Rocks is in the Cimarron National Grassland, the largest parcel of publicly accessible property in Kansas. The land here was taken out of production following the Dust Bowl, in an attempt to slow soil erosion. Today it's a place of short-grass prairie that seems to have more in common with the landscape of the southwestern U.S. than the rest of Kansas. It's a place of quiet, austere beauty. And the site of a long-running geologic mystery.

Point of Rocks is capped by naturally cemented rocks in the Ogallala Formation. This is the same Ogallala Formation that holds water underground. Here it crops out at the surface. But beneath that Ogallala Formation are bright red shales and siltstones, and tan sandstones. They're obviously older than the overlying Ogallala. But how much older? When were they deposited?

Until now, nobody knew. Geologists use fossils to provide a rough age date of the rocks they're found in. But because these red formations at Point of Rocks contained virtually no fossils, nobody knew what time period they belonged to. Think of it as a blank spot in the geologic map of the state. We know the age of virtually every other rock formation at the surface, and even most in the subsurface.

But here is an outcrop, in a fairly visible place, and geologists could only guess about its age. Over the years, some geologists said those rocks were deposited in the Cretaceous Period, about 100 million years ago, the same age as the rocks that crop out in the Smoky Hills of central Kansas. The most recent geologic maps call them Jurassic, about 150 million years old. Yes, the same Jurassic as the Steven Spielberg movies.

Now, after applying age-dating techniques to zircons, small crystals found within the red rocks at Point of Rocks, scientists at the Kansas Geological Survey here at KU have decided that they are probably Permian, deposited about 265 million years ago. They're roughly the same age as rocks that make up the Flint Hills in east-central Kansas and the Red Hills down by Medicine Lodge.

Geologic maps are the beginning point for all sorts of things, from road building to water well drilling to sand and gravel mining. They're the touchstone for knowing the land and what you can do on it. Filling in this spot may not seem like a big deal, but it represents an improved understanding of the surficial geology of the state. It helps connect the dots between the outcropping rocks in Morton County and the surrounding area.

It's a small step. But science moves in increments, some big, some little. In this case, it's produced a bit more knowledge about this place. And that's something we should all care about. ####

Scientists Solve Age-Old Geologic Mystery in Southwest Kansas


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