We hear this a lot. Hey, we're not botanists or conservation planners, but here's a quick answer to get you thinking some more about the forest!
The cross timbers is a term used to describe the cross timbers ecoregion, an area of similar soils, plants, and animals that ranges from Texas northward through Oklahoma and into Kansas.
East & West Collide
Perhaps it's easiest to remember this term by thinking of the cross timbers as that ecoregion where you'll find some species of plants at the westernmost fringe of their existence - and some at their easternmost existence... where they cross. There are perhaps other interpretations, but we'll offer this one for starters.
The area is comprised of mostly blackjack oak, post oak, and some eastern red cedars. Throughout this ecoregion (and the Keystone Ancient Forest) you'll find patches or even large swaths of prairie remnant, with big and little bluestem grasses.