Explorations and Surveys for the Pacific Railroad. 73 



route. It is probable that all the routes are nearly on an equal- 

 ity in this respect. 



The cultivable valleys of the Kocky 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 be- 

 tween the Cceur 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 de- 

 scend 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 pro- 

 ductive 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 construction 

 of irrigating canals, is now cultivated by the Mormons. Here 

 also are extensive grazing lands. 



The great elevated plain of the Eocky 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 and almost the 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 scat- 

 tered growth of stunted cedars is likewise seen. Water is found 

 on the mountain side. The predominating rocks, from the Wah- 

 satch mountains to the Sierra Nevada, are of igneous origin. 

 In the 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, Eio 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, ex- 

 clusive 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 



SEEOND SERIES, VOL. XXII, NO. &4. — JULY, 1856. 10 



