Early maps of North America, prepared in the 18th and early 19th centuries, often depicted the Llano Estacado as a conspicuous blank spot - a terra incognita.  A good example is a map of the southwest sketched by Alexander von Humboldt in 1804.  In 1830, Stephen F. Austin added little detail to the definition of the Llano Estacado in his "Map of Texas" where he simply labeled an unspecified region as "level prairies" with "immense herds of buffalo."  In 1844, Josiah Gregg made the first serious attempt to define the boundaries of the Llano Estacado.  Gregg's map correctly places the Llano Estacado to the east of the Pecos River, to the south of the Canadian, and shows tributaries of the Red, Brazos, and Colorado rivers along its eastern margins.  Thirty-four years later, geologist William F. Cummins led a party of five men as they traveled entirely around the Llano Estacado as part of the Third Geological Survey of Texas.  Based on this reconnaissance, a fairly detailed map was published in 1891 that provided a more precise definition of the boundaries of Llano Estacado.  During the 20th century, more accurate information regarding the features of the Llano Estacado has led to more precise maps.  Examples include maps constructed by Johnson (1901), Smith (1931), Theis (1937), Raisz (1957), Wendorf (1975), Osterkamp and Wood (1987) and Holliday (1995).  Despite these advances, there remains some disagreement regarding the boundaries and the overall size of the Llano Estacado.  Here an attempt was made to better define the boundaries of this vast region.