Explorations and Surveys for the Pacific Railroad. 69 



These mountains may be considered as constituting three 

 great systems, extending generally throughout our possessions 

 in a north and south direction ; and although this arrangement 

 may not be the best or most accurate, yet it will enable us to 

 take a comprehensive view of the whole as regards the construc- 

 tion of a railroad, since any direct line that can be traced from 

 the Mississippi to the Pacific, except near the 48th and 32d 

 parallels, will encounter each of these three systems in some 

 point. 



Calling the most eastern system No. 1, we find a portion of it, 

 crossing the Kio Grande, and entering Texas at the Great Canon. 

 Its extension south into Mexico forms the east front of the Sierra 

 Madre. Eunning northward, this system includes all the moun- 

 tains on either side of the Eio Grande, enclosing its valley and 

 the Salinas Basin. Those on the east form the divide between 

 the Pecos and Salinas Basin, and between the Eio Grande and 

 Canadian ; on the west they divide the waters of the Eio Grande 

 from those that flow to the Gulf of California. Those on the 

 east are sometimes called the Eocky mountains, sometimes the 

 Sierra Madre ; and this last name is sometimes applied to those 

 on the west. There seems to be a necessity for considering the 

 mountains on both sides of the Eio Grande as one system. 

 These may be said to unite near the headwaters of the Eio 

 Grande and Arkansas, and here the mountains have their great- 

 est development. The Sierra de la Plata extends to the south- 

 west, the Elk mountains to the west, and the various chains 

 forming the Park mountains to the north. The Park moun- 

 tains, in latitude 41° 30', sink into the plateau, forming the re- 

 gion of the South Pass ; and the only continuation we have of 

 this system is in the Black Hills, which continue to the north, 

 with diminished elevation, till, in latitude 46° 15', they are 

 merged into the coteau through which the Upper Missouri makes 

 its passage. 



Among the mountains included in this system are the Sierra 

 Madre, a portion of what is called the Eocky mountains, the 

 Diabolo mountains, the Guadalupe mountains, Hueco mountains, 

 Organ mountains, Sandia mountains, Santa Fe mountains, Sierra 

 Blanca, Sierra Mojada, Sierra San Juan, Sierra de la Plata, Elk 

 mountains, Park mountains, Medicine Bow mountains, and Black 

 Hills. 



System No. 1 is thus but partially gorged by the Eio Grande, 

 whose passage of the Great Canon is wholly impracticable for 

 any method of communication ; that of El Paso is practicable. 

 It is completely cut through by the North Platte and Sweet 

 Water, forming a practicable route ; and is turned by the Upper 

 Missouri. 



