There is very little public land in Texas. Aside from the national park/forests/grasslands and state parks, lots of camp sites are private owned land and you almost have to hear about them from someone. You're not really going to pass by these places incidentally on state highways between rural towns because you'd have no reason to go out there otherwise. I'm sure there are many interesting places tucked away on giant ranches (some of which are as big as counties, or even the state of Rhode Island) which aren't available to the public. Hell, when the government went to buy Big Bend, they had to survey the land in order to make an offer to the people with the deed - meaning that nobody, not even the people who technically owned the land, had ever really been there and explored it in its totality. That's how thoroughly sold and owned Texas land is.
