Department o-t Technology' for partial fulfillment of the requirements for the degree 'Doctor of Philosophy. Hodge, perhaps the chief scientist for the CAscade Hange in Oregon, has published several papers~. A paper on Mount Jefterson2 was based on fairly short field studies, but gives a good general idea of the volcanic history of the peak and the surrounding area.
In 1928, Hodge set out his views on the portion of the Ranee between the LlcKBnzie and the North Santiam Rivers. The axes of the major anticlines of the Western Cascade are shown in black; the Cascade fault and structural axes of the High Cascs des are shown in red.
C PTER II
PLATE 6
Hills, the structural or opposite extension of the Salem Hills, fight red from the northern end of the Salem Hills. The homoclinic structure of the bills is quite clear, and some landslides, topography can be seen along the western soarp. B nch in the foreground is the ~orm on the basal flow of Stayton Lavas.
PLATE 7
That the rhyolIte 1s was carried down to the.aa t 1s is indicated by its absence in the north of Sant1::un hlver south of the El, at a distance from the junction of the Behelor Trail.. as suggested by HQdge1 • indicates that the . In t.h /ortb Sa tl Hlver\there 1s Do noticoable minor l1zatlon. sl1ckensidos ero no~cd. one mile east of the:'~oCoy Creek trail. Four It&rnato by thoQ0smay x- plain t steep slope Ohar ot r of the eternal 0 ge of the deaite sr-.
Spire Rock, one of the intrusive outcrops of the Outer-son Complex, seen from the trail to the southwest. The truncated crests of the High Cascades are visible to the left; the interior plain' is the surface of Pigeon Prairie, to the right of the present valley of the North Santiam River.
PLATE 10
South of the Elbow, the rock-cut valley of all the former series" was probably not less than a mile and a half wide opposite the ";woodpecker ridge, and rose rapidly to the south. The northwestern projection of t. !tehama antic11ne nearly coincides with the Eagle Creek anticline of Oolumbia Gorge, moreover. The similar projection of the Breitenbush anticline lies in the vicinity of the Ortl and Bingen anticlines.
While the western Oascade folds trend northeast-southwest, the veins and associated dllts (l1or1tlc dllt of the entire Western Cascade system in Oregon strike northwest. Basin Range-type faults have been described 1n the Klamath e:rag by G1lbert1, a .nd. the scarp to the south of the 1l,ake crater is usually considered. It seems therefore unlikely that the faulting of this could determine the distribution of the High Cascade vents.
The location of the Outerson and Pigeon grafts along the Cascade Escarpment is a good example of this. The small distribution of the volcanic centers in the High Ca-cade is strongly suggestive of such a connection. This system of Basin Range-type faults diagonally transects the northeastern western Cascadefolda, cutting it off completely south of the Pneitenbush River.
The general andesitlo nature of the lavas in the Casc de Range was recognized 'or at one time, probably. Except for the Cr tel' Lake district a detailed study of the Range bas beau Illnlted to tbe structure. Their light weight is due to their porosity, ..mcl transparency' glo.so bases.
PLATE 12
The finer root mro denaer, aho ,~od. on in oat of them, a II bUM nt in ny. nt piroxem: i t OCC C pbonooryots nd in tho ,rOUl'l<1WS. of Gold Butte obotts tlO separate ne lnr aot pbenocryota ~ ytotlnlte, is 2.5. Tl yto nita ioo nurroundc ' b1 Vi . of tU'ldenine, 1st plunder tbat the anda inc.. i,ntereot1n~ hot1over. rOI" the opportunity t nff'ordu tor tracing flo 0 outt1 £l?om the atual ccnter of ruption.. talnlng bund nt hotley-colored pyroxenos6.
PLATE 13
PLATE 14
The High Cascade lvaa are very light gray basalts, usually containing olivine or hypersthene, the upper part of the Minto series, but were not observed elsewhere. The Fill City Glacier crossed one-third the width of the ""eastern Cascades; the ice barely penetrated the east side. The total thickness of the cash register is approximately thirty meters. Torth of Ilill City turned red. Rainy deposits are visible at about 1.0 out of 1000 hours. ' A.
It contains striated and faceted unsled boulders of all sizes and representative of practically all rock types of the Santiam district. Although the destruetif"n of the p-lac1al profile in the l'"rra could have been supplied very quickly, the planati'ln ()f . massive lava. streams, and for tt"m of t e later terraces Wf)uld require much time. gray till in river gravel exposed in the road cut at the east end of.
Breitenbush River Highway bl>ldge, and to the site 1n 1n a cut road half a mile southwest "f Ber.;oy.. The exposures are all very small; .. to 1s very similar to r disease it, in the compactness, amount of matrix, freshness, and arrangement of the rocks. The Detroit glaciation is extensive and must have greatly modified the topography "in the High Cascades. The portrait was probably taken during this time. Accordingly, Detroit until the first century was tentatively connected to the Tahoe Glacier of the Sierra Nevada.
The mar ains and physiography of the latt glaciat1on, Tunnel Creek, a.re for the most part, well preserved. No morainic topog.l"8.fi observed; river slides and planimetry" caused partly by landslides farther eo ilnstree.m have removed all but a little of that. The only recessional moraine observed in the Breitenbush drainage is at 2900 fe8t in the South Fork valley.
PLATE 17
Looking east down the glaciated valley of the Whitewater' River from the head of the cirque at the east end of Jefferson Park. Washington, and the three sisters are visible on the skyline beyond the ridge formed by the Outerson depos:l,ts. The observer looks south from a point a thousand feet above the floor of the park.
The trees grow on 10 VI basalt soils that were probably formed by the edges of more and more lava flows. Jefferson is covered in Battle Ax lava, as is the hill west (right) of Dunlap.
PLATE 22
PLATE 24
- XXXIV
Small remains of a high terrace, sloping about three degrees to the southwest, occur at 2,800 and 1,700 feet on the other side of Tumble Oreel:c, which has been diverted about ft quarter ,~ mile southwest. The hill in the center of the valley appears to have been part of the old bed, which is well preserved south of the Morth t3antlanl. North of this hill , and west of ~reiten'bu8h Elvor tr is an extensive gravel terrace at an altitude of:3.tlon approx. These rough r~.ver ~ra.vels . are well ~x:)osed in Breit~nbush ro d.1just north of Detrolt.
The panorama of the High Ctllscades from Woodpeoker IIill to Pine Ridge I llS seen from Bachelor Mountain. From north to south the main features are: the valley of WhitevTater Creek; Woodpeoker Hill, composed of Outerson deposits;. Jefferson, rising above the valley of Prun.ella Creek; Mintoberg; Minto Creek and Bingha:.m Basin;.
PP built up by flo s from acid 06, located near the course of the t. The North Eitenbush valley is 6.1 degrees left of center; Bald Butte 1s directly west. The lower level of the Breitenbush River can be seen from right to left.
PLATE 34
0' the steep current moves in the eastern cascades, which diverted the long western foot of the lligh cascades, or were reversed in direction. The topography left by the Mill City gla.oier was probably largely destroyed during the Detroit Ice Age. The Isconsin glaciation apparently followed Detro-it closely enough so that cirques of the latter still existed.
The basal contact relationships of the lavas indicate that the pre-lava landscape was in the mature phase of the erosional cycle. In the western part of the area, the Illahe Formation mainly consists of sandy or silty tuffaceous sediments, with occasional thin pebbly water beds. Incomplete weathering of claystones indicates a rather rapid transport and deposition of sediments.
Complete list of identified species from the Illahe Formation in the vicinity of the Salem Hills. Division of the Illahe Formation into distinct famlal zones is not possible at this time. In view of the above data there can be little doubt that the Illahe Formation of the Salem Hills should be correlated with the Eugene and Pittsburg Bluff Formations in the Middle Oligocene.
The size of the unconformity between them and the Illaha Formation indicates that the lavas are much younger than the marine deposits. In addition, the Columbia River Middle ~,(iocm:le Columbia River) lavas except tr8,ce to the southern edge of the Estacada ~uadrangle on the west side of the Cascade Range. The Staytonian lavas thicken to the north and are very likely a thin margin of the Columbia lavas.
