LLANO ESTACADO. The Llano Estacado, commonly known as the Staked Plains but perhaps more accurately interpreted as the “palisaded” plains in geological terms, is the southern extension of the High Plains of North America and lies south of the Canadian River in northwest Texas and northeast New Mexico. A high mesa sloping at a rate of approximately ten feet per mile toward the southeast, it is one of the largest tablelands on the continent. This high flat land is located approximately between 101° and 104° west longitude and 31° and 35° north latitude. It is distinctly bounded on the north by the southern escarpment of the Canadian River valley and on the east by the irregular and deeply incised Caprock escarpment. The western boundary is the Mescalero Escarpment east of the Pecos River valley of New Mexico. The southern end of the plateau lacks a distinct physical boundary; it blends into the Edwards Plateau, and the Johnson Creek branch of the Colorado River, east of Big Spring, is probably best considered its boundary.
Full article on the Texas State Historical Association's Handbook of Texas Online