DESCRIPTION OF THE REGION. V 



Bandera, Gillespie, Kendall, and Blanco counties, as well as half of 

 Crane, Upton, Tom Green, Irion, Concho, Menard, Travis, Hays, 

 Comal, Bexar, Medina, Uvalde, and Kinney counties. This area is a 

 part of the great limestone region which constitutes the southern 

 province of the Great Plains. To the northwest it is continuous 

 with the Staked Plains, and is a typical open, level plains countr}^ 

 Farther southward, hoAVCA^er, the area is far advaiiced in the process 

 of erosion, being deepl}^ dissected b}^ streamways flowing southeast- 

 ward and cutting the margin into long, narrow tongues of the former 

 plateau mass. In the dissected border are also hundreds of remnantal 

 buttes or hills, like Mount Bonnel and Lone Tree Hill at Austin, 

 Long Mountain, Post Mountain, Pack Saddle, etc." (See frontispiece 

 and PI. I, fig. 1.) 



The Edwards Plateau (Eighteenth Ann. Rpt. U. S. Geological Sur- 

 vey, p. 206) presents three simple topographic elements: (1) The 

 flat-topped summits of the deca^ang plateau (the divides); (2) the 

 breaks and slopes of its crenulated borders and canj^oned valleys 

 ("the mountains"); and (3) the streamways or rivers and their 

 branches. 



The escarpment front rises to an elevation above the Coast Plain of 

 from 400 feet at Austin to 1,000 feet in Uvalde County, while the 

 northwest is a high plain 2,1:00 feet above the sea. Naturally, it is 

 chiefly in the eroded or mountainous portion of the plateau that a pro- 

 tective timber growth is needed. 



For our present purpose the important considerations concerning 

 the Edwards Plateau are, that it is a vast receiving area for rainfall, 

 and that its structure is such as to give special significance to the 

 behavior of water after it has been precipitated. 



STRUCTUKE OF THE EDWARDS PLATEAU AS A CATCHMENT AREA. 



Until the report by Messrs. Hill and Vaughan was published there 

 seeuis to have been no general recognition that this limestone country 

 played a role of consequence as a receiver of precipitated water. The 

 report showed, however, that, as a matter of fact, its capacity to take 

 up water is of the first importance; and that this is possible not only 

 because of the specific absorption capacit}^ of the limestones them- 

 selves, but also by reason of the favorable exposure (b}^ erosion and 

 normal outcrop) and the tilting of the strata, and especially b}^ reason 

 of the very extensive systems of fissures and caverns, which contribute 

 remarkably toward rendering the formation receptive of water. 



«Hill and Vaughan. Artesian Water of the Edwards Plateau, etc., Eighteenth 

 Ann. Rpt. U. S. Geological Survey, Part II. 



The above report has been used freely in the preparation of this bulletin, and 

 grateful acknowledgment is hereby made of the author's indebtedness to it. 



