CHAPTER Y 
GEOLOGY OF THE CASCADE MOUNTAINS. 
Panoramic view of the cascade mountains.—Sierra Nevada and cascade mountains.— A wall crowning the western margin 
OF THE GREAT CENTRAL PLATEAU.—STRUCTURE AND ORIGIN OF THE CASCADE RANGE-MAIN CREST NEAR ITS EASTERN MARGIN A LINE 
OF VOLCANIC PEAKS.— MORE WESTERLY MOUNTAINS, METAMORPHIC SLATES.—LOCAL GEOLOGY.—CRATER PASS—EVIDENCES OF 
GLACIAL ACTION.—GLACIERS ONCE DESCENDED FAR BELOW THE PRESENT SNOW LINE.—EXTENT OF GLACIERS IN THE CASCADES.— 
Conditions under which they must have been formed.— By elevation or change of climate ?—Evidences of elevation.— 
Sub-aerial excavations of mouths of rivers.—Depression of temperature would produce greater precipitation of 
moisture —Streams flowing from the cascade mountains formerly larger than now.—Canons of these streams not 
rifts but excavations. 
After reaching the head-waters of the Des Chutes river, we ascended the main fork of that 
stream to its source, in the Cascade mountains, spending a month crossing and recrossing the 
main crest, latitude 44° north, in the vicinity of the Three Sisters. The mountains which have 
received this name form part of a group of five, of which only the three most westerly are 
visible from the Willamette valley, and have been known to the residents. The altitude of the 
loftiest of the group is about 10,000 or 11,000 feet above the level of the sea, the line of 
perpetual snow being 7,000 feet. This group of mountains marks an angle or joint, if I may 
use the expression, in the Cascade range. Standing on the summits of the passes between them, 
we saw the main crest of the range crowned by several peaks of considerable altitude, hut 
particularly marked by the lofty and snow covered cones of Mount Jefferson and Mount Hood, 
trending away nearly due north. Looking southward, we saw the belt of the Cascade moun¬ 
tains, so broad above, narrowed in its limits, trending southwest by south, marked by no 
conspicuous peak, and yet continuous to the point where the sharp, snow covered cone and 
broad base of Mount Pitt bounds the horizon in that direction. There, another joint marks a 
deflexion of the chain to the south, a course which it holds till lost in the huge mass of Mount 
Shasta ; there again deflected to the eastward, to he again turned south at Lassen’s butte. This 
mountain system seems like some grand fortification, as though Nature, when the broad plateau, 
which reaches inland from its base, was redeemed from the sea, had built along its western 
margin a wall of such altitude as should forever hid defiance to the waves, and at all the 
salient or re-entering angles had planted towers which should strengthen and command the 
whole. 
Looking north from the Three Sisters, and viewing the Cascade mountains in profile, we saw 
that the axis of the range was set nearest to its eastern border, and that the descent from this 
crest to'the plateau which forms its base in that direction was made by few and steep declivities; 
while toward the west stretched a broad belt of mountains which gradually diminished in alti¬ 
tude, and, as we subsequently learned, more than fifty miles distant, were lost in the foot hills 
which border the Willamette valley. 
This section seemed to afford us some clue to the manner in which this range had been formed. 
The series of principal peaks marks the line of fracture in the earth’s crust, along which the 
greatest exhibition of volcanic forces would naturally he displayed. Toward the east, the great 
