Reason for this was to avoid the almost inpenetrateble "Monte Grande" . The large post oak and blackjack forest that bisects the state from deep south Texas almost to the Red River.
You mean the Cross Timbers? It runs clear up here. I used to live in it, now I live close to the eastern edge of it. The Cross Timbers is some beautiful country.
http://en.wikipedia.org/wiki/Cross_Timbers
