EXAMINATION OF THE ROUTES. - 7 
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 
route. It is probable that all the routes are nearly on an equality in this respect. 
The cultivable valleys of the Rocky mountain district near the route of the 47th parallel do 
not probably exceed an area of 1,000 square miles, though there are extensive tracts of fine 
grazing lands. In this latitude the great sterile basaltic plain of the Columbia, and the barren 
table-lands, spurs, and mountain masses of the Cascade range, principally occupy the space 
between the Coeur d’ Alene mountains and the main chain of the Cascade system. In this area, 
where the rocks are principally of igneous origin, there are likewise occasional valleys of culti- 
vable soil. The western slopes of the Cascade mountains descend to the borders of Puget sound, 
On the routes of the 41st and 38th parallels, in the region under consideration, the only 
large body of soil capable of productive cultivation, by the construction of suitable works for 
irrigation, is that of the basin of the Great Salt lake, estimated to be 1,108 square miles 
in extent, about one-tenth part of which, being susceptible of cultivation without the construc- 
tion of irrigating canals, is now cultivated by the Mormons. Here also are extensive grazing 
lands. 
The great elevated plain of the Rocky mountains in latitudes 41° and 42°, and that of latitude 
38°, called the San Luis valley, are covered with wild sage, the narrow border of grass found 
upon the streams being the chief, almost only, production capable of supporting animal life. 
The slopes of the mountains bounding them are covered with grass. 
‘ The plains of the Great Basin, whose greatest width (500 miles) is in latitude 41°, are, with 
the exception heretofore stated, entirely sterile, and either bare or imperfectly covered with a 
scattered growth of wild sage. Where a stream or lake is found in this desolate region, its 
immediate borders generally support a narrow belt of grass and willows; the former being also 
found on the mountain slopes, where occasionally a scattered growth of stunted cedars is like- 
wise seen. Water is found on the mountain-side. The predominating rocks, from the Wahsatch 
mountains to the Sierra Nevada, are of igneous origin. Inthe southern portion of the Basin 
the granitic rocks are more abundant than the volcanic. 
On the routes of the parallels of 35° and 32° the valleys of the Pecos, Rio Grande, Gila, and 
Colorado of the West, contain the largest areas of fertile soil capable of irrigation and cultiva- 
tion. That in New Mexico is estimated at 700 square miles, exclusive of the regions occupied 
by Indians, of which 200 square miles are now under cultivation. Here the grazing land 
is of very great extent, the table-lands, as well as the mountain-sides, being covered with grass. 
The valley of the Colorado of the West, between its mouth and the 35th parallel, contains 
1,600 square miles of fertile soil, which can be irrigated from the river. 
The plains south of the Gila in its lower course, and that west of the Colorado, extending to 
the Coast range, called the Colorado desert, as well as the contiguous portion of the Great 
Basin, are bare and exceedingly sterile in their aspect, and closely resemble each other. The 
soil of the Colorado desert, and much of this as well as other parts of the Great Basin, is, how- 
ever, favorably constituted for fertility, but the absence of the essential, quickening element, 
water, leaves them utterly unproductive. 
West of the Coast, Sierra Nevada, and Cascade mountains the country is better watered 
than that just considered; and the soil being mostly well constituted for fertility, is productive 
in proportion to the yearly amount of precipitation and the means of irrigation. 
The general position and direction of the four routes to be explored were explained in my 
report of December 1, 1853, and copies of the instructions given to the parties were appended 
to it. 
They were directed to observe and note all the objects and phenomena which have an im- 
mediate or remote bearing upon the railway, or which might seem to develop the resources, 
peculiarities, and climate of the country; to determine geographical positions, obtain the topo- 
graphy, observe the meteorology, including the data for barometric profiles, and two of the 
