^fii0 la HIGH PLATEAUS. 



the mass about 6 miles long and 



ifipas^ble talua surrounds the scarped 



the ascent difficult except at a few points 



.as are homblendic trachytes and eugili- 



A and made up of ntimerous flows. Thc^ 



i«<wer Tertiary, of which the thickness is not precise!.- 



*t well exceed 700 feet Whether the diminished 



;ere is due to an originally small amount of depo- 



the upper members prior to the volcanic oveiflow 



■.t T incline to the former • explanation. And the 



that over the area occupied by the eastern 



• lunand Lake Mountain the Tertiary deposition 



sewhere. Immediately beneath is the 



<Jretaoeou8 is absent frrtm ,it8 place in tJ.m 



'^w miles t«> the northe:wtward the whole 



atd np . ' ■' ''it3 slopes of a grand 



.;..,. -vW, which ^a probably the grand- 



au Country, so far as known, and per 



Its first appearance is beneath Thousand Lake 



Sheet No. 4), wliere the trend is east'isQMtheast and it 



^ound towanla the 80uth-soutb«jajjt, reaching to the Colo- 



!Ti the heart of the Glen CafSon. It crosses the river into 



regions. Upon the northwestern side of the mountain it is cov- 



'•' Tertiary beds and lava sheets fuid is wholly concealed, so that 



> northern nor its southern termitrttious are at present known. 



; fault U{Km the wes^t si<W of the mountain cuts across this mono- 



rlv -.'J: n;rht anjrlo.s, :sn»^ \v>9. dr '^vt^d the platform to the west 



xure is evidently older thiir. 



nearly horizontally across 



Htem and upon the deeply- 



rh aa the entire body of 



liie Lii. t ,ir in succession as we 



;ure and a.s ir mod upon its flanks, 



