CHAPTER V 



GEOLOGY OF THE CASCADE MOUNTAINS. 



PANORAMIC VIEW or TUB CASCADE MOUNTAINS. SIERRA NEVADA AND CASCADE MOUNTAINS. A WALL CROWNING THE WESTERN MARGIN 



OF THE GREAT CENTRAL PLATEAU. STRUCTURE AND ORIGIN OF THE CASCADE RANCE MAIN CREST NEAR ITS EASTERN MARGIN A LINE 



OF VOLCANIC PEAKS. MORE &quot;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 

 MOISTURB. STREAMS FLOWING FROM THE CASCADE MOUNTAINS FORMERLY LARGER THAN NOW. QANONS 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, ii 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, but 

 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 be 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 bid 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 be displayed. Toward the east, the great 



