When the area of Kansas we are current traveling thru was first settled it was mostly treeless. No trees, no fence posts, so what did those settlers do? They used what was available which was a relatively thin band of limestone that resisted weathering and became known as fencepost limestone
The post in front of our RV site.
This limestone was formed from deposits when the Western Interior Seaway covered this part of Kansas during the Late Cretaceous period many millions of years ago. The post at our RV site has a shell showing. The post rock limestone has been designated the official state rock of Kansas.
Corner posts needed additional bracing. We saw this example at a nearby State Park.