68 Explorations and Surveys for the Pacific Railroad. 



The western portion of the continent of North America, irre- 

 spective of the mountains, is traversed from north to south by a 

 broad, elevated swell or plateau of land, which occupies the 

 greater portion of the whole space between the Mississippi river 

 and the Pacific ocean. The crest of this plateau, or the water- 

 shed of the country, is nearly midway between the Pacific coast 

 and the Mississippi. It may be represented on the map by an 

 undulating line traced between the headwaters of the streams 

 which flow eastward and those which flow westward. It divides 

 the whole area between the Mississippi and the Pacific into two 

 nearly equal portions — that on the east being somewhat the 

 larger. This crest of the water-shed has its greatest elevation 

 in Mexico ; and thence declines to its lowest point about the 

 latitude of 32°, where it has a height of about 5,200 feet, be- 

 tween the waters of the Eio Grande and those of the San Pedro, 

 a tributary of the Gila. From this parallel it increases in alti- 

 tude northward, and reaches its maximum near the 38th parallel, 

 where it is about 10,000 feet high. Thence it declines as we 

 pass northward; and, in latitude 42° 24', it has an elevation of, 

 say, 7,490 feet ; and in the latitude of about 47° it is reported 

 to be at least 1,450 feet lower. The heights here given are those 

 of the lowest passes over the crest or water-shed of the great 

 plateau of the country, and not those of the mountain peaks and 

 ridges which have their base upon it, and rise, in some cases, to 

 the height of 17,000 feet into the region of perpetual snow. 



The slope of the plateau on the east and south, towards the 

 Mississippi and the Gulf of Mexico, is comparatively gentle, and 

 in the northern part of Texas, that known by the name of the 

 Llano Estacado, or Staked Plain, is by steps. It is traversed by 

 the Missouri, the Platte, the Arkansas, and other large rivers, 

 which rise among the mountains near the crest, and flow east- 

 ward and southward in channels sunk beneath the general sur- 

 face-level of the plains. 



The crest of the mountains, and nearly the entire distance 

 thence to the Pacific, is occupied by high plains or basins, dif- 

 fering from each other in elevation from 1,000 to 3,000 feet, and 

 by mountain peaks and ridges, varying in direction to almost 

 every point of the compass, though they have a general course 

 north and south. Many of these mountains, including those that 

 bound this system, have obtained the name of chains, and a short 

 classification of them will now be attempted, although it is to be 

 premised that our knowledge of them is most imperfect, and the 

 classification now made, future explorations will probably show 

 to be erroneous. The only proper classification must be made by 

 the geologist, after a thorough exploration for this purpose, which 

 it will require a long period to accomplish. 



