DESCRIPTION OF THE RKGION. 9 



Handera, (iillespie. Kendall, and Blanco counties, as well as half of 

 Crane. I'pton. Tom (ireen, Irion. Concho, Menard. Travis, Hays, 

 Comal. Hexar. Medina, I'valde, and Kinney counties. This area is a 

 part of the great limestone region which constitutes the southern 

 province of the (ireat Plains. To the northwest it is continuous 

 with the Staked Plains, and is a typical open, level plains country. 

 Farther southward, however, the area is fur advanced in the process 

 of erosion, being deeply dissected by streamways flowing 1 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, 

 Lono- Mountain, Post Mountain, Pack Saddle, etc/' (See frontispiece 

 and PI. I, tig. 1.) 



The Kdwards Plateau (Eighteenth Ann. Rpt. IT. S. Geological Sur- 

 vev. p. ^M>) presents three simple topographic elements: (1) The 

 flat-topped summits of the decaying plateau (the divides); (2) the 

 breaks and slopes of its crenulated borders and canyoned valleys 

 ( u the mountains-'); and (3) the streamways or rivers and their 

 branches. 



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

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

 northwest is a high plain 2,-iOO 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. 



STIircTriJK <)I THE EDWARDS PLATEAU AS A CATCHMENT AREA. 



I'ntil the report by Messrs. Hill and Vaughan was published there 

 seems 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 capacity of the limestones them- 

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

 normal outcrop) and the tilting of the strata, and especially by 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. I". S. CJeologiral 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. 



