72 Explorations and Surveys for the Pacific Railroad. 



along the whole range, with, a width varying from 250 to 300 

 and 400 miles. 



From the foregoing sketch it will be perceived that the lines 

 of exploration must traverse three different divisions or regions 

 of country lying parallel to each other, and extending north and 

 south through the whole of the western possessions of the Uni- 

 ted States. The first is that of the country between the Missis- 

 sippi and the eastern edge of the sterile belt, having a varying 

 width of from 500 to 600 miles. The second is the sterile re- 

 gion, varying in width from 200 to 400 miles ; and the third, 

 the mountain region, having a breadth of from 500 to 900 miles. 



Explorations show that the surface of the first division, with 

 few exceptions, rises in gentle slopes from the Mississippi to its 

 western boundary, at the rate of about six feet to the mile, and 

 that it offers no material obstacle to the construction of a rail- 

 road. It is, therefore, west of this that the difficulties are to be 

 overcome. 



The concurring testimony of reliable observers had indicated 

 that the second division, or that called the sterile region, was so 

 inferior in vegetation and character of soil, and so deficient in 

 moisture, that it had received, and probably deserved, the name 

 of the desert. This opinion is confirmed by the results of the 

 recent explorations, which prove that the soil of the greater part 

 of this region is, from its constituent parts, necessarily sterile ; 

 and that of the remaining part, although well constituted for 

 fertility, is, from the absence of rains at certain seasons, except 

 where capable of irrigation, as uncultivable and unproductive 

 as the other. 



This general character of extreme sterility likewise belongs to 

 the country embraced in the mountain region. From the west- 

 ern slopes of the Kocky mountains to the 112th meridian, or the 

 western limit of the basin of the Colorado, the soil generally is 

 of the same formation as that lying east of that mountain crest, 

 mixed, in the latitudes of 35° and 32°, with igneous rocks ; and 

 the region being one of great aridity, especially in the summer, 

 the areas of cultivated land are limited. The western slopes of 

 the highest mountain chains and spurs within this region being 

 of a constitution favorable to fertility, and receiving much larger 

 depositions of rain than the plains, have frequently in their 

 small valleys a luxuriant growth of grasses, which sometimes 

 clothes the mountain-sides; and where the wash is deposited 

 along a mountain valley or river-bottom the soil is fertile, and can 

 be cultivated, if the elevations are not too great, and the means 

 of irrigation are available. Such mountain- valleys and river-bot- 

 toms exist upon all the routes, and the difference in the areas 

 found in the different latitudes is not sufficiently great to be of 

 any considerable weight in determining the question of choice of 



