CHAPTER VI, 
GENERAL REMARKS ON THE TOPOGRAPHY OF THE MOUNTAIN REGION 
WEST OF THE MISSISSIPPI. 
THE mountains in our territory west of the Mississippi river, from where they rise above 
the horizontal strata of recent geological formations on the east to their disappearance under 
the waters of the Pacific Ocean, form a nearly continuous mass of upheaved ridges, with 
occasional intervening level plateaus. The direction of the central line of this mass between 
the 32d and 49th parallels of north latitude, is about north 20° west. The greatest width 
perpendicular to this direction is along the line passing from the vicinity of San Francisco 
through that of the Great Salt Lake to Fort Laramie. This distance is about 1,000 miles, or, 
if we include the Black Hills of Nebraska, 1,125 miles. 
The great mountain mass, of which that in our territory forms but a part, aninda with 
varying breadth nearly on the line of a great circle of the globe from Cape Horn north to 
Behring Straits, and thence south along the western part of Asia to the island of Sumatra. 
Its length is about 240 degrees, or 18,560 miles, being two-thirds of the circumference of 
the earth. 
The area occupied by and included in this mountain mass in our territory, is about 980,000 
square-miles. Large as this is, it is probably only a small portion of the upheaved formations 
between the 32d and 49th parallels. A few ridges and peaks projecting above the surface of 
the Pacific as islands, or above the level tertiary and cretaceous strata of the eastern plains, 
give evidence of the existence of vast areas whose extent must forever remain unknown. 
Throughout the portions now visible, proofs are abundant of great abrasions; in some cases 
whole ridges even, having been swept away or broken into separate portions. 
Already enough has been learned to establish the existence in these mountains of the equiva- 
lents of many of the geological formations; and it is probable, when investigations have been 
carried to the same extent as in the civilized portions of the earth, that the geologist will 
find here new and still more complex fields for research. 
"The classification of the separate parts of this mountain mass, so as to present its physical 
characteristics clearly to the mind, is a great desideratum. It has in part been attempted at 
various times, but as yet unsuccessfully from the want of sufficient information; the theorist’s 
idea being often proved to be wrong by new discoveries almost as soon as uttered. 
In this immense field, many years of patient labor are yet necessary before any. تمس‎ 
classification of these mountains on geological principles can be made, even if it ever be in the 
power of human research and understanding. The practical wants of the geographer, of 
the meteorologist, and of the engineer, will not permit of this delay; and numerous general 
descriptions and theories to supply the want of facts have been attempted by them for the 
purpose of more clearly explaining their views. In this way mountain ridges have sometimes 
been improvised for the occasion, and the want of facts supplied by ‘‘ generalizations and ideal 
