232 GEOLOGY OF TRANS-PECOS TEXAS. 



TOPOGRAPHICAL NOTES. 



In examining the topographic features of West or Trans-Pecos Texas we 

 find a continuous rise from the Rio Grande on the west and south and from 

 the Pecos River on the east, towards the Guadaloupe Mountains and their 

 continuations. These form the eastern and highest mountain chain crossing 

 this part of the State in a direction extending from southeast to northwest. 

 This ascent is not gradual on the west, but over two other mountain ranges, 

 the Diabolos and Huecos and tneir southward continuations. 



Although the Chinati Mountains, the Sierra Corazones, Chisos, and St. 

 Jago reach nearly as high above the surrounding flats and valleys — that is 

 about 2000 feet — as the Guadaloupe, Sierra Blanca, Apache or Limpia, and 

 Quitman mountains, their altitude above the sea level is lower by at least 1000 

 feet. The fall of the Rio Grande from El Paso to the Devil's River is about 

 2700 feet, and that of the Pecos River from Pecos City to its mouth nearly 

 1500 feet, thus giving a considerable fall from the New Mexico line towards 

 the southeast. 



Directly north of El Paso on the left bank of the Rio Grande, rises the 

 Franklin range. On the east side of this range the mesa rises to a height 

 of 250 feet above the river bottom, which here extends for a width of 3 

 to 4 miles between the river and the mesa. The mesa itself extends over 

 the entire region between the Franklin and the Hueco mountains, form- 

 ing a flat about 25 miles wide, and extends also into New Mexico, and is 

 there connected by a gap between the Franklin range and the Organ Moun- 

 tains with the river bottom itself some 25 miles above El Paso. This mesa 

 extends also east of the Hueco Mountains, but removing further and further 

 from the river and also toward the Sierra Blanca Mountains, where the pass 

 through which the Southern Pacific and Texas Pacific railroads run reaches 

 the altitude of 4648 feet above the sea level, a rise of 1100 feet above the 

 river bottom at Fort Hancock in a distance of less than 25 miles. From 

 this summit at Etholen the country descends for 9^- miles to Arispa, forming 

 there a flat basin, the deepest part of which (4500 feet above the sea level) 

 covers nearly 30 square miles. The sides of this basin rise gradually, aver- 

 aging about 100 feet in from 6 to 8 miles. The flat is terminated on the 

 west and southwest by the foothills of the Quitman, Sierra Blanca, and Eagle 

 mountains, with gaps or openings to the smaller flats or valleys towards 

 the Rio Grande; on the north by the foothills of the Sierra Diabolo; while 

 it opens on the east into the broad flat north of Van Horn, and through Bass 

 Canyon into the large flat between the Van Horn and Davis mountains. 

 These flats ascend gradually toward the north above Van Horn, and to the 

 southeast towards Valentine and Ryan stations on the Southern Pacific Rail- 



