The plains (Central and Western Oklahoma) are fairly rock free and big ag areas. I have hunted west of Dogdoc and out there a rock was a real rarity. So much so that any rain at all on a dirt road and you would be stuck because of the red clay type dirt they have over that way. I know this from experience because I got stuck twice in the middle of the county road in a 4 wheel drive. Over here where I live you can drive anywhere anytime with a rock base under you everywhere you go but it is different out there.
Oklahoma has lots of characteristics of many states such as mountains, deserts, forest, plains, swamps, etc...