These are found in the Ozarks of Missouri and Arkansas, too.
For a related bit of obscure US history you can read about the post-civil war vigilante group named after these: https://en.wikipedia.org/wiki/Bald_Knobbers
For a related bit of obscure US history you can read about the post-civil war vigilante group named after these: https://en.wikipedia.org/wiki/Bald_Knobbers
The hills to the north of the White River Valley (around Springfield) and south (south of Harrison) are capped by rock layers that have a relatively high clay content and produce soil that can more easily support forests.
The Bald Knobber history is pretty interesting. I had always thought of them as analogous to the earliest KKK (also a Reconstruction-era vigilante group initially) but I hadn't realized until I read the surprisingly detailed Wikipedia page that the Bald Knobbers were Republicans who sided with the North. (Unfortunately, the Bald Knobbers are history at this point, while the KKK is still quite active in the area, especially Harrison/Boone County, Arkansas).