I don't know the answer to this one, but one long-ago professor at OU used to say that Oklahoma was "a state of four halves: the East half and the West half (and) the North half and the South half."

The East/West division separates the Five Civilized Tribes from the Plains Indians each with radically different cultures.

The North/South division is obvious in that veterans from Union states settled south of the Kansas line, while veterans from Mississippi, Alabama, Texas, and various other Confederate states settled the area below the Canadian River.