F.M. 669 south toward Gail reaches edge of Texas High Plains called the Llano Estacado, which are southernmost extension of Great Plains of the U.S. In immensity beyond comprehension the Great Plains sweep north more than 1,600 miles, thrusting deep into Canada through the heartland of America that produces nation's abundance of grain, meat and fiber. Highway descends the abrupt edge where plains end, traveling through panoramas of steep cliffs and colorful canyons.