338 PROCEEDINGS OF THE ACADEMY OF [1893. 



escarpment ; and about fifty miles west of here is another escarp- 

 ment, facing west, which makes the western edge of the Llano Esta- 

 cado. These plains are narrow here, this being the southern angle 

 of the triangle formed by these bounding escarpments. The plains 

 themselves are gently undulating and unscored by erosion. Farther 

 north they are traversed by deep canons, but here almost no drain- 

 age lines are apparent. 



(6) River Valleys Abandoned through Dessication. — A careful 

 study of these plains along the eastern part of the Llano Estacado 

 will reveal some interesting facts, and I believe it is to the drainage 

 lines that we will have to look for a solution of the history of this 

 region. I can do no more than throw out a hint. The streams have 

 carried more water than at present. This may show nothing more 

 than a decrease in rainfall, or it may be the key to a complicated 

 history. 



From the Red Fork of the Colorado River, near Colorado City, 

 to the Pecos, a distance of not less than one hundred and seventy- 

 five miles, there was not, in April, 1890, a single flowing stream, yet 

 the maps show several large branches of the Colorado crossing the 

 line travelled. Three of these in particular, Girard Creek and 

 two branches of the Concho River, are on the map made to rise far 

 up in the Staked Plains. The Concho I crossed without being 

 aware of the fact, for the valley of each branch is a broad valley 

 with gently sloping sides and no channel. This is not a case of 

 " arroyo " type of drainage, that is, a channel which occasionally 

 carries floods. It is an old abandoned valley. 



Girard Creek, which I was able to study more carefully, is of the 

 same type, but less distinctly dessicated, being intermediate in degree 

 of abandonment between the Colorado proper and the Concho. 

 From Big Springs westward for six miles the valley averages a mile 

 in width and is bounded by degraded bluffs from fifty to one hun- 

 dred feet in height. There is no channel, but the valley bottom is 

 a series of alkaline flats of the playa type, between cone deltas 

 formed by the wash from the valley sides. These alluvial cones 

 frequently extend completely across the valley and are overgrown 

 by mesquite, showing quite plainly that no flow of water occurs in 

 the valley. The flats between these cones resemble in appearance 

 the estuarine marshes of the northeastern coast. Below Big Springs 

 the channel is clear, and the drainage is young, being of the strong 



