That stuff is all over our property in Freestone County. A little research told me ours is palm wood, between 60-80 million yrs old. I have found some nice size chunks of it, a few tree trunks still largely intact but they break up when digging them up. The house built from recycled box cars that my grandfather was born and raised in used petrified wood for the piers. We'll get some nice chunks out of that when we clean up the old home site.
I see people freak out when they find a hand sized piece of petrified wood, I grew up finding it everywhere on the property so it's never been a big deal to see it.
The old family homestead in Freestone Co has it all over the place, like you said trunks mostly intact. Strange that it's right on top of the ground.