196 GEOLOGICAL SURVEY OF THE TERRITORIES. 



nia. The other is the Great Salt Lake basin, whose waters empty into 

 the lakes contained within it, or are lost in the sands of its plains. 



THE EASTERN DIVISION. 



As before stated, this division includes all the territory under consid- 

 eration which lies east of the divide between the waters of the Atlantic 

 and Pacific. It embraces the areas drained by the Rio Grande, the Ar- 

 kansas, the Platte, (or rather the Plattes.) and the Big Horn Rivers and 

 their tributaries. These areas, although very irregular and unequal, are 

 generally separated from each other by very distinct boundaries, and 

 can be traced without difficulty. 



The Rio Grande basin, although belonging to this division, because 

 its waters find their way to the Atlantic, is in fact situated in a bifur- 

 cation of the Rocky Mountain range, pointing southward. And as the 

 larger and loftier extension of this bifurcation is the eastern prong, the 

 basin lies west of it. The western rim of this division, which is the 

 divide between the waters of the east and the west, beginning at the 

 southern extremity and going northward, runs about as follows : With 

 the Mimbres Mountains to the plains of San Augusta; thence slightly 

 northwest along the Zuni range to Campbell's Pass, where, turning north- 

 east, it passes along Mesa Fachada to the Sierra de San Juan, which 

 forms the western rim of the San Luis Valley. From the vicinity of 

 Coochetopa Pass, running west of tbe Upper Arkansas Valley, and 

 west of South Park, it suddenly turns eastward and winds around Mid- 

 dle Park, throwing this basin on the west. North of this it again bends 

 westward around the North Park, where the character of the range is 

 again changed. Losing its compact form, it breaks up into irregular 

 branches and broken chains, separated by elevated intervening plains, 

 which are traversed by short ridges and mountains. The main divide, 

 which is less elevated here than farther south, bends somewhat abruptly 

 to the northwest, connecting with the Wind River Mountains, near 

 South Pass. The latter range forms the western boundary of the Big 

 Horn basin, the northern district of the division under consideration. 



The eastern boundary of this division, as fixed by nature, is the line 

 where irrigation becomes necessary as we move west from the Mississippi. 

 But since this is difficult to determine definitely, I have limited my ex- 

 aminations to the boundaries of the three Territories within which the 

 work of the expedition was principally confined during 1869 and 1870. 

 This embraces nearly all of New Mexico, the eastern half of Colorado, 

 and (by including the Powder River country) all of Wyoming, except 

 a small triangular area in the southwest corner, and amounts in the 

 aggregate to about two hundred and fifty thousand square miles. 



Of this area perhaps three-tenths, or seventy-five thousand square 

 miles, could not be cultivated if every other obstacle except its rugged- 

 ness were removed. Of the remaining seven-tenths we may set down 

 five-tenths as at present without a sufficient supply of water for irriga- 

 tion. This leaves two-tenths, or about fifty thousand square miles, which 

 are, or may be rendered arable by irrigation, and which, at a moderate 

 estimate, would support a population of several millions. It is true that 

 this is but an estimate in round numbers, liable to be considerably modi- 

 fied, and which will, by many, be considered as exaggerated, but I make 

 it after having traversed the entire division from one extremity to the 

 other; and I believe it will prove to be nearer correct than the limited 

 estimates which have heretofore been made in regard to the cultivable 

 lands of these Territories. And I think it quite probable that addi- 





