How did Texas get its shape?

AMARILLO, Texas (KAMR/KCIT) - Defined in seven natural regions by the Texas Parks & Wildlife Department, the state of Texas stretches over 268,597 square miles. It reaches as far west as to be within spitting distance of White Sands National Park in New Mexico, and as far north as the Rita Blanca National Grasslands.
Texas is large enough to house tropical beach destinations to the south and the frigid, awesome expanse of the Llano Estacado in the Panhandle, with an immense collection of wil