In Texas, a LOT of the land is separate from the mineral rights. In the early to mid 1900's speculators offered money for mineral rights and people sold off their minerals. Farmers for the most part, back then, were poor (and some of them were uneducated and ignorant) and a check for something ambiguous, unseen, and un-used was a wonderful thing. Now, not only are there mineral rights, but wind rights too! I have seen land for sale with the wind rights reserved. The LAST thing i would want camped out on my property would be a bunch of wind turbines!
I had a friend whose father and grandfather were both doctors. His grand father rode his horse to make house calls. People were so poor (this was in the 1920's - 1950's) that they did not have money to pay him with and he told them to will their mineral rights to him, which many of them did. My friend and his brother developed those mineral rights, drilling for oil and became wealthy. He now has oil wells all over east Texas and when cell phones came along, he started putting up cell towers. $$$$$$$