GEOLOGY OF THE BREITENBUSH
HOT SPRINGS QUADRANGLE,
OREGON
1980
STATE OF ORI::GON
DEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES
DONALD A. HULL, STATE GEOLOGIST
STATE OF OREGON
DEPARH1ENT OF GEOLOGY AND MI NERAL INDUSTRI ES
1069
State Office Bui l d i ng, Portl and , Oregon
97201
Special Paper 9
GEOLOGY OF THE BREITENBUSH
HOT SPRINGS QUADRANGLE,
OREGON
CRAIG WHITE
Department of Geol ogy and Geophysics
Boise State Univer s i ty , Boise , ID 83706
1980
Conducted i n conformance with ORS 516.030
Funded i n part under U.S. Department of Energy Contract DE FC 07-79-ID-12044
to the Oregon Department of Geology and Mineral Industries
GOVERNING BOARD
John L . Schwabe, Chairman
Robert W . Doty
C. Stanley Rasmussen
Portland
Talent
Baker
•
STATE GEOLOGIST
Donald A . Hull
DEPUTY STATE GEOLOGIST
John D. Beaul ieu
Photomicrographs on page 10 were reversed by printer and are printed
ERRATA SHEET:
This sheet shows correct placement of photos and captions.
in wrong order.
a. Scorpion Mountain lava flow (CT-8);
small plaaio�lacc phenocryst in rround­
mass of plagioelase rnicr'Olil-es� gr>anulta>
pyPoxene and opaque ore.
b.
Elk Lake Formation� dacitic lava (CTc.
28); amph1:bole, orthopyroxene� and plag­
ioelaae 1'n finely Cl'lJGtnllinc groundmaaa.
d. Outerson Formation, basaltic flow from
the base of the formation;
large olivine
c�atals in ophitic grotmdmass of olivine,
plagioclase and opticaUy continuous mono­
clinic pyroxene (CT-17).
e.
Outerson Fo1mation, basaltic andesite
flow (CT-68); corroded olivine and small
phenoa�ats of plagioclase in �roundmass
oj' plagioclas�� two pyroxenes, and ore.
f. High Cascade lava flow, �iddle Pleis­
tocene basaltic andesite; small olivine
phenocrysts in pilotaxitic groundmass of
plagioclase and two pyroxenes (CT-51).
hypersthene, and monoclinic pyroxene in
a matrix of black glass and fine c�stals
�
Fi)UI'e 6.
Elk Lake Formation, andesitic flow
(CT-59); phenoc�sts of plagioclase,
Photomcrographs of lavas from the Breitenbush Hot Springe quadrangle.
are at the same scale so that the height of each photo is equal to 1.6
10
All
mm.
C
N T E
0
N T
S
I NTRODUCTION
Fie 1 d and Laboratory P rocedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . .
.
GENERAL STRATIGRAPHY OF THE NORTH-CENTRAL CASCADE RANGE I N OREGON
..
..
.
.
. .
. .
Rocks of Late O l i gocene and Early Mi ocene Age
Rocks of Middl e and Late Miocene Age . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .
Rocks of P l i ocene and Quaternary Age
. . .
. . . . . . . . . . .
.
. . .
.
. . . .
. . .
. .
DESCRIPTIONS OF UNI TS I N THE BREITENBUSH HOT SPRINGS QUADRANGLE
............ .
Breitenbush Formation
. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ... .... ... . . .
Scorpion �1ountain Lavas . . . . . . . . . . . . . .... . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E l k Lake Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Outerson Formation
. ... . .. .... ... .. .... .... ... .... .... ..... ... .... ... ... .
High Cascade Lavas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
.
.
DESCRIPTIONS OF STRUCTURES I N THE BRE ITENBUSH HOT SPRINGS QUADRANGLE
.........
1:
3
5
6
8
8
8
9
11
12
15
17
REFERENCES
APPENDIX
3
. . .
.
K/Ar AGES OF SAMPLES FROM THE BREITENBUSH HOT SPRINGS QUADRANGLE
19
APPENDIX I I: CHEMICAL ANALYSES OF SAMPLES FROM THE BREITENBUSH HOT SPRI NGS
QUADRANGLE . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
APPENDI X I I I .
24
LOCATIONS OF ANALYZED SAMPLES
I L L
U
..................... ... . ... .....
S T R A T I 0 N S
PLAT E :
Geo l ogic map o f the Breitenbush Hot Springs q uadrangle
--
. . . . . . . . . . . in envelope
FI GURES:
1.
Index map showing l ocation of the Breitenbush 1 5-minute quadrangl e
2
2.
Correl ation chart of formations in the north-central Cascade Range in
Oregon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
iii
3.
H i s togram of K/Ar ages of vol ca n ic rocks i n the north-central Cascade
Range i n Oregon ....................... . .. ... . ... .............. . . . . . . .
5
AFM rel a tions for l avas of l ate Oligocene and Mi ocene age i n the northcentral Cascade Range i n Oregon
6
H i s tograms of S i 02 content of samples from the Brei tenbush Hot Springs
quad rang 1 e
. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
Photomi c rographs o f lavas from the Breitenbush Hot Springs
quadrangle
. . . . . . . . . . . . ... .... . . . . . ... . . . . . . . . . . . . . . . . . .. . . . . . . . .. .. .
10
A plot of S i 02 versus the ratio FeO(total )/FeO(tota l ) + �1g0 for
samples from the Breitenbush Hot Springs quadrangl e . . . . . . . . . .
11
.
4.
.
5.
.
. . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
6.
.
7.
.
8.
9.
. .
.
. .
.
A plot of S i 02 versus total alkal i contents for samples of Pl i ocene
and Pleistocene age from the Breitenbush Hot Springs quadrang l e
12
Plots of P20s , Ba , and the rat i o K/Ba versus a di fferentiation index
for samples from cones and vents along the H i g h Cascade crest i n the
Brei tenbush Hot Springs quadrangle
. ..
. . . . . . . . . . . . . . . . . . . ... . .
14
L i neament map drawn from high-alti tude i nfrared photographs of the
Brei tenbush Hot Springs area
... .... ......... ..... .... ..... . ........
16
. .
10.
.
.
.
. . .
.
. .
COVER PHOTO:
Photomi crograph of basal tic andesite bomb from the surrm i t of O l a l l i e Butte.
NOTICE
The Oregon Department of Geol ogy and Mineral Industries
is publ i sh i n g th i s paper because the subject matter is con­
sistent wi th the m i s s i on of the Department. To facilitate
timely d i stribution of i nforma t i o n , camera-ready copy sub­
mi tted by the author has not been edi ted by the staff of
the Oregon Department of Geology and Mi neral Industries .
iv
GEOLOGY OF
SPRINGS
THE BREITENBUSH
HOT
QUADRANGLE, OREGON
INTRODUCTION
This report summarizes the resul ts of a geol ogical and geochemical s tudy of the
vol ca n i c rocks i n the Breitenbush Hot Springs 1 5-minute quadrangl e . The map area i s
bounded by 44°45 ' and 45° N . l ati tudes and by 1 2 1 °45 ' and 1 22° W . l ongi tudes and i s
l ocated whol l y w i th i n the north-central part o f the Oregon Cascade Range ( Figure 1 ) .
It i n c l udes a part of the High Cascade p l a tform north of Mt. Jefferson as wel l as the
eastern edge of the Western Cascade Provi nce. Rocks i n this area range from l ate
Ol i gocene to l a te P l e i s tocene i n age and are a l most entirely of vol can i c ori g i n .
The purpose of this study i s to provide geological i nformation that can b e used i n
the eval uation of the Oregon Cascades a s a potent i a l geothermal resource. The Brei ten­
bush Hot Springs area was sel ected because i t i nc l udes the boundary between the Tertiary
rocks of the Western Cascades and the Quaternary l avas of the High Cascade crest. The
fact that the contact i s marked by a 1 i ne of hot springs al ong about 200 km of i ts
l ength has l ed geo l o g i sts to speculate that i t may be the s i te of a major fau l t system.
Al l en ( 1 966) sugges ted that t h i s zone marks the western boundary of a north-south
trend i ng graben wh i ch has been fi l l ed by H i g h Cascade l avas . A fault-contro l l ed boundary
for the eastern margi n of thi s proposed structure has been identified by Taylor ( 1 980 ) ,
but fau l ts al ong the western s l ope are obscured by vegetation and have been traced for
no more than a few kilometers . In t h is terra i n , the l ocation and throw of major faults
general ly can be i nferred only if stratigraphic relationsh i ps are wel l understood and
l arge- scal e d i spl acements can be recognized . The stratigraphic data presented on the
geolog i c map i n P l ate 1 and 1n the accompany i ng text provide new i nformat ion on which
to i nterpret structural relations in the Breitenbush Hot Springs quadrangl e and i n
adjo i ni ng parts of the Cascade Range .
Field and laboratory Procedures
Mappi ng was accompl i shed during the l ate summer and early autumn of 1 97 9 , and the
prel imi nary map was revi sed and compl eted i n June of the fol l ow i ng yea r . Geologi cal
contacts are based primari l y o n the d i s tr i bution of rock types exposed in road cuts
a l ong the extensive system of l ogging roads in the area . Large or cri tical ly located
outcrops identified on aer i a l photographs were v i s i ted by foot.
Fi fty-s i x samples were analyzed for major and selected trace e l ements on a Varian
(AA- 1 75 series) atomic absorption spectrometer. Ferrous i ron analyses were made by
ti tration, and the water contents of a l l samples were determined with a Du Pont e l ec­
tronic mo i s ture analyzer. Analytical accuracy was checked by i nc l uding two standard
rocks with the analyzed specimens and by determi n in g the major-el ement contents of four
samples by both atomic absorption and X-ray fl uorescence methods . The K/Ar ages of 1 1
whole-rock samples were determined i n order to provide chronol ogical control for strati­
graphic and structural i n terpretations.
Acknowledgments
This project was carried out under a grant from the Oregon Department of Geol ogy
and Mi neral Industries w i th funds provided i n part by the Uni ted States Department of
Energy. Gordon Goles and Al exander McBi rney revi ewed the text and contri buted helpful
suggestions . Jul i e White aided in preparation of the camera-ready copy .
MT. HOG.Q
4
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THREE f1NGERED JACK
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Figure 1.
Index map
in
1 0
N
Miles
t
20
showing the Z.ocation of the BreUenbush Hot
2
Spri'YI{JB quadroa'YI{Jle.
GENERAL STRATIGRAPHY OF THE NORTH-CENTRAL CASCADE RANGE IN OREGON
The Cascade Range in Oregon was divi ded by Cal l aghan ( 1 933) into two major sequences
on the basis of a marked structural and l ithol ogi c break. The Western Cascade Series
consists of a structura l ly deformed and local ly a l tered sequence of andesitic fl ows ,
andesitic to rhyodaci tic pyroc l a s t i c rocks , and subordinate fl ows of basal t , dacite, and
rhyolite. T h i s sequence i s over l a i n by the rel atively undeformed and primari ly basal tic
l avas of the H i g h Cascade Series.
Peck and h i s co-workers ( 1 964) summari zed previ ously publ ished s tudies and their
own reconnaissance mapping in a comprehens i ve report in which they subdivi ded the West­
ern Cascade Series into three units : the Celestin Formation ( l a te Eocene) , the L i t t l e
Butte Volcanic Series (Ol i gocene and early Miocene) , a n d the Sardine Formation (midd l e
and l a te Miocene). Field mapping and radiometric dating in recent years have shown that
the strati graphic rel ations i n many areas of the Cascade Range do not readily conform to
Peck's regional system. I n this report I wi l l fol low a stratigraphic scheme based
l argely on the one suggested by McBirney and others { 1 974) for the north-central Cascades.
The names and ages of units in t h i s area are shown on the schemati c col umn in Figure 2 ,
a l ong with the stratigraphic column of Peck and others ( 1 964).
The revisions made by McBi rney and his co-workers ( 1 97 4) fol l owed the recogn i tion
that radiometric ages of Western Cascade l avas erupted s i nce middl e M i ocene time tend
to c l uster at interval s of roughly five m i l l ion years. Additional ages of whole rocks
from the north-central Cascades tend to confirm t h is trend {Figure 3 ) . Because lavas of
each age group represent a s i ng l e wides pread episode of volcanis m , they have been
assigned to four separate formations: the Sardine Forma t i on {midd l e Miocene ) , the E l k
Lake Fonnat i on { l ate Miocene) , the Outerson Formation {Pl i ocene ) , and the H i gh Cascade
lavas (Quaternary) . Radiometric ages of l avas erupted prior to midd l e Miocene time do
not c l uster at well-defi ned peaks; instea d , the l imited data i ndicate that volcanism was
sporadic a l l y continuous throughout the interval between 1 9 and 30 m. y . Rocks erupted
during this time have been subdi vided into two interfingering u n i ts on the basis of their
contrasting l ithol ogic character.
Some specific features of the stratigraphy in the north-central Cascade Range are
discussed below. Detailed l ithologic and petrographic descriptions of many units are
presented in previously publ ished reports {Thayer, 1937, 1 939 ; Peck and others , 1 964 ) ,
and for this reason the present discussion is confined primarily to new interpretations
or recently a cquired data.
Rocks of Late Ol i gocene and Earl y M i ocene Age
The oldest rocks exposed in the north-central Cascades con s i s t of pyroc l a s t i c fl ows ,
vol cani c breccias , and basal tic to rhyodaci tic lavas. Hammond { 1 97 9 ) appl ied the name
"Breitenbush Formation" to these rocks where they crop out i n the upper Breitenbush and
Col l awash river val l eys. They are equivalent to the Breitenbush Tuff of Thayer ( 1 939)
and are s i mi l a r in stratigraphic position and l ithol ogy to parts of the L i t t l e Butte
Volcanic Series of Peck and others {1 964). The age of the i gnimbrites and breccias
that comprise the l ower part of the formation is not wel l known owing to the difficul ty
of determining radiometric ages for a l tered pyroc l as tic rocks ; however , l avas overlying
these units con s i s tently yield K/Ar ages between 20 and 27 m. y.
Intercal ated within the tuffs and tuffaceous sediments i n the midd l e and upper
parts of the Breitenbush Formation is a distinctive sequence of flows that I have
i nformal l y named the Scorpion Mountain l avas . These rocks are exposed in the Calapooya ,
Midd l e San t i a m , North Santiam, and upper Col l awash drainage systems as wel l as in the
3
Peck
and
others (1964)
White (this report)
::::>
HIQi CASCADE
�
HIGH CASCADE
0
....
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....
:£
r:C.-"MBIA R.
BASALT
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ELK LAKE
COLUMB
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FORMATION
Tuffaceous
e-.
10.
FORMATION
�J.I I I I I I I I I I I I I I
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5
OUTERSON FORMATION
SARDINE FORMATION
�
MY
VOLCANIC SERIES
....
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sediments
-:::::::-
breccias
20
SCORPION
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15
2.5
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Figure 2.
COLESTIN FORMATION
40
Correlation ahal't of fo1'17'1:J. tioru; in the north-aentra'l Casaade Range in Oregon
Western Cascade foothi l l s near Eugene. They have been mistakenly identified as part of
the Col umbia River Group but yield l ate Ol igocene and early Miocene K/Ar ages and were
vented locally within the Western Cascade region . Lavas in this unit are invariably
dark col ored and genera l ly appear aphanitic in hand specimen ; despite their uni form
appearance, however, they range in composition from basal t through dacite . I n thin
section , most samples contain a few phenocrysts of plagioclase and cl inopyroxene , but
only the most mafic s pecimens have modal ol ivine.
The Scorpion Mountain l avas have been shown to represent a geochemical l y d i s tinct
rock series that differs markedly from the calc-a l ka l ine associations genera l ly thought
to be typical of Cascade lavas (W h ite and McBirney , 1 979 ) . Thi s trend can be c l early
seen when anal yses of l avas from the north-central Cascades are pl otted on a ternary
AFM diagram ( Figure 4 ) .
The Scorpion Mountain l avas define a trend of iron-enrichment
that is characteristic of the thol eiitic rock series , whereas middl e and l a te Miocene
l avas from the Sardine Formation display l ittle or no iron enrichment. The dashed l ine
in Figure 4 serves to separate the compositional fields of ''classic" thol eiitic and
cal c- a l kaline suites ( Irvine and Baragar, 1 97 1 ) .
4
0
5
1 0
..,
"'
Q
Figur'e 3.
15
20
Histogram of K/A'l' ages of
vo�aanic 'l'ooks in the north­
centra� Cascade Range in
Oregon. Data are f'l'om
Sutter (1 97 8), Hanrnond and
othe'l's (1980), and White
(thiiJ I'el_)uL•t).
25
30
1234567
No. of
Samples
In addition to the contrasting trends in iron enrichment, the Scorpion �1ountain
lavas differ compositionally from younger Cascade lavas by having generally lower contents
of MgO, CaO, Al203, Sr. Ni, and Cr, and higher contents of Ti02• K20. Rb, Zr, Ba, and Sc.
These differences are especially striking for rocks with compositions of basaltic
andesite and andesite.
Although several models have been proposed to explain geochemical
differences between tholeiitic and calc-alkaline rock suites (e. g., Kuno, 1 966; Ring­
wood, 1974 ) , the contrasting trends observed in Cascade lavas can be explained best by
The trends in the Scorpion
a shift in the assemblage of early-stage phenocryst phases.
Mountain lavas are consistent with early fractionation of olivine + plagioclase + Crrich spinel ± clinopyroxene, whereas the compositions of the younger calc-alkaline rocks
indicate early removal of amphibole± clinopyroxene± olivine.
The shift from an olivine­
dominated fractionation scheme to one controlled by amphibole may indicate a change in
the water content of the parental magmas or an increase in the depth of primary magma
reservoirs, either of which could serve to stabilize amphibole in basaltic magmns.
Rocks of Middle and Late Miocene Age
Thayer ( 1 937, 1 939 ) first applied the name "Sardine lavas" to the flows nnd pyro­
clastic rocks of middle and late Miocene age that cap the ridges and peaks near an
Peck and his co-workers
eroded vent complex at Sardine t·lountain, northwest of Detroit.
( 1 964) re-defined the Sardine Formation to include all Western Cascade lavas that
5
70
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Figure 4.
88
.,
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o oo
0 0
Qo o 0
M
AFM { (Na20
+ K20)
: MgO : FeO(total)} relations for lavas of late Oligocene
and �oaene age in the north-central Cascade Range in Oregon. Solid circles
repPesent analyses of late Oligocene and early �ocene Scorpion Mountain lavas,
open oiroles represent analyses of middle and late Mio�ene lavas of the
Sardine and Elk Lake Formations.
Data are from unpublished sources and are
on computer file at the University of Oregon Center for Volcanology.
occupy a stratigraphic posi tion between the dominantly pyrocl astic rocks of the L i tt l e
Butte Vol ca n i c Series and the l ava fl ows o f the H i g h Cascade Seri es . I n the north­
central Cascades , the Sardi ne Formation cons i sts of andes i ti c fl ows and lahars i nter­
bedded with subord i nate volumes of basalt and tuffaceous rocks. Most lavas i n this unit
are noti ceably porphyritic and contain abundant phenocrysts of plagioclase . Ol i vine
and c l i nopyroxene are common phases i n Sa rd ine basalts but give way to hy persthene as
the most abundant mafic mine ra l i n the andes i t i c and dac i t i c lavas . The textures and
mineral contents of these rocks se rve to d i sti nguish them from the aphyr1c and
hypersthene-free l avas of the Scorpion Mountain sequence.
tkBirney and h i s co-workers (1974) d i vi ded the Sardine l avas i nto two formations.
They reta ined the name "Sard i ne Format i on" for the voluminous rocks of midd l e Miocene
age , but rec ogni z ed a less volumi nous sequence of l ate Mi ocene l avas which they named
the E l k Lake Formation. At its type l ocality about 10 km north of Detro i t , the Elk
Lake Formation consists of a se q uence of rhyodaci t i c f l ows and tuffs and subordi nate
fl ows of hornblende andesite that unconformably overlies folded rocks of the Sardine
and Breitenbush Formations . South and east of Detroi t , rocks of E l k Lake age i nc l ude
dark-colored f l ows of olivine basalt. T he El k Lake Formation i s probably equival ent to
the pyroclast i c rocks and andesitic flows of the R hododen dron Formation which overl i e
the Columbia River Basa l t i n the region west of Mt. Hood.
Rocks of Pliocene and Quaternary Age
The rel ati vely unaltered basal ts and basaltic andes i tes that unconformably over l i e
Mi ocene and Ol i gocene rocks of the Western Cascade Range were defined by Ca l l aghan ( 1 933)
and later by Peck and others (1964) as the High Cascade Series . Thayer (1937, 1939)
d i vided the H i g r Cascade Series in the Mt. Jefferson area i nto three age groups: an
6
older sequence of strongly faulted and dissected flows and breccias (Outerson lavas), an
intermediate sequence of basaltic shield lavas (Minto and Battle Ax lavas), and a young
series of flows and pyroclastic rocks that were erupted from the vents and cones that
comprise the present-day High Cascade crest ( Olallie lavas). New radiometric age
determinations for rocks from the north-central Cascade Range indicate that post-Miocene
volcanism in this region took place during two distinct episodes , one about four to six
million years ago and a second beginning about two million years ago and continuing to
the present time. McBirney and others {1 974) assigned the lavas erupted during the
earlier episode to the Outerson Formation and restricted the term "High Cascade" to lavas
of Quaternary age.
Most lavas in the Outerson Formation were erupted from vents located along the
eastern margin of the Western Cascades. They consist primarily of finely porphyritic
olivine-bearing basaltic andesites which appear in marked contrast to the coarse-grained
pyroxene andesites that comprise most of the lavas of the Elk Lake and Sardine Formations.
Lavas with mildly alkaline geochemical affinities have been identified near the base of
the Pliocene volcanic sect i on at widely scattered localities in southern Oregon (Maynard,
1974 ) , in the area west of Ht. Washington (McBirney , 1 968) , and in the Breitenbush Hot
Springs quadrangle (this report). Naslund ( 1978) showed that these lavas are also
enriched in Ti02, P 20 5 , and Zr rel ative to younger Pliocene and Quaternary rocks, and
he suggested that t h ese compositionally distinctive lavas may form the base of the
Pliocene-Pleistocene Cascade chain along much of its extent in Oregon.
The High Cascade lavas consist of basaltic to rhyodacitic flows and breccias that
were erupted initially from broad shield volcanoes and later from small to large
composite cones located primarily along the High Cascade crest. The early Pleistocene
High Cascade lavas are not notably different in composition or appearance from the bulk
of lavas in the Outerson Formation. They consist primarily of olivine-bearing basalts
and basaltic andesites with intergranular or diktytaxitic textures. Taylor ( 1 980) noted
that diktytaxitic basalts in the central High Cascades are commonly overlain by late
Pleistocene basaltic andesites with pilotaxitic textures. The many composite volcanoes
that cap the High Cascade platform in north-central Oregon consist primarily of basaltic
andesite and andesite, with subordinate volumes of basalt, dacite, and rhyodacite being
important constituents in some cones. Most of the large volcanoes. such as Mt. Jeffer­
son and Three Fingered Jack , were built during two or more discrete eruptive episodes,
each of which produced a compositionally distinctive suite of lavas (Sutton, 1 97 4; White ,
1 980; Davie, 1 980 ) .
7
DESCRIPTIONS Or UNITS IN THE BREITENBUSH HOT SPRINGS QUADRANGLE
The l ithologic , petrograph i c , and geochemical character i s t i c s of the various mapped
units of Pl ate 1 are summa rized below. Chemi cal analyses of sel ected samples are gi ven
in Appendix I I . Rock names are based on silica content (H,O free) according to the
method used by Taylor ( 1 978) for lavas in the SW Broken Top quadrangl e . Subdivisions
are made at five-percent i ncrements of Si02 for basa l t (48-52 ) , basal tic andesite (5357 ) , andesite ( 58-6 2 ) , dacite ( 63-67 ) , and rhyodacite ( 68-72) ; the Si02 contents of a l l
anal yzed samples are pl otted as histograms in Figure 5 . Textural terms are based on the
classification of Wil l iams (1954) .
Breitenbush Formation
Pyroclastic fl ows and vol canic breccias of the Breitenbush Formation crop out in the
extreme western edge of the map area a long val l eys formed by the Brei tenbush and Col l a­
wash Ri vers . The vol canic sediments consist of massive, coarse-grained breccias of
fl uvial origin interbedded with thin units of vol canic sandstone and air-fa l l tuff. The
pyroclastic flows contain abundant coarse fragments of pumice and l ithic debris and are
general ly gray or pa l e green in color.
A parti cularly d i s t i nctive rhyodacitic ash flow i s exposed a l ong the Breitenbush
River for about two km west of the Breitenbush Campground ( sees . 1 9 and 2 0, T. 9 S . , R .
7 E . ) . This uni t consists of pumice, l ithic fragments , and broken crystal s of pl agio­
c l ase and quartz in a matrix of gl ass shards and fine ash . Its characteristic pale­
green color is caused by finely disseminated cel adoni te within the ashy portions of the
matrix. Pl agiocl ase from this ash flow has yielded K/Ar ages of l ess than 20 mi l l ion
years (Sutter, 1 978; Hammond , 1979 ) ; however, these ages are a l most certainly too young ,
because rocks exposed at stratigraphi c l evel s above t h is unit yield whole- rock K/Ar ages
as o l d as 24 mil l ion years (Sutter, l g 78 ) . Hammond ( 1 979) a l so obtained a f i s s i on-track
age of 27 mil l i on years for the ash f l ow , and this val ue is more consistent with the
known ages of other rocks in the area .
Scorpion Mountain Lavas
Dark-colored aphanitic l avas cap Scorpion Mountain ( sec . 5 , T. 9 S . , R. 7 E.) and
crop out in i so l ated exposures on the steep s l ope north of Breitenbush Hot Springs and
a l ong the east side of the Col l awash River val l ey . A possible vent area for some of
these flows is i ndicated by the numerous dikes and bedded aggl omerate exposed in road
cuts a t the 3600-ft l evel west of Mansf i e l d Creek ( sec . 9 , T. 9 S . , R . 7 E . ) . An
exhumed vol cani c neck that forms Eag l e Rock. about five km west of Breitenbush Hot
Springs, may a l so have been the source of some Scorpion Mountain l avas in the map area .
Rocks in this unit range i n composition from basal tic andesite to dacite. Lava
flows have pil otaxitic textures and contain sparsely distributed phenocrysts of pl agio­
cl ase and serpent i n i zed monocl i nic pyroxene {Figure 6a ) . Groundmass mineral s include
pl agioc l a s e , opaque ore, and pyroxene, some of which has been tentatively identi fied as
pigeonite on the bas i s of its very sma l l opt i c ang l e .
Analyzed samples of Scorpion Mountain l ava differ i n chemical composition from most
other Cascade lavas by having l ower val ues of CaO, Al203 , MgO, and Sr: higher val ues of
Ti02 , Rb, and Ba; and greater iron enrichment. The tholeii tic af finity of these samples
is demonstrated by Fi gure 7, in which the ratio FeO( tota l ) /FeO(total ) + MgO is pl otted
versus S i 02 . The Scorpion Mountain l avas plot wel l within the tho l eiitic field , as
defined by Miyashiro (1974 ) , whereas most samples from younger units plot c l ose to or
within the cal c-alka l ine fie l d .
8
so
ss
55
10
HIGH CASCADE
10
OUTERSON FM.
10
ELK LAKE FM.
10
SCORPION MT. LAVAS
70
u
z
....
=
c:r
....
""
...
...
_.
....
:IE
.,
Figurs 5.
Histograms of Si02 content
qua.drang le.
of samples from the B�eitenhush Hot Springs
Scorpion Mountain lavas within the map area are similar in composition and strati­
graphic position to other Cascade tholeiites that have yielded late Oligocene or early
Miocene radiometric ages. A flow from near the top of the Scorpion Mountain section in
the map area yielded a whole-rock K/Ar age of 19.4 million years (Appendix 1).
Elk Lake Formation
Flows and pyroclastic rocks of the Elk Lake Formation crop out at numerous locations
in the northern, western, and southern parts of the map area, where they overlie rocks
of the Breitenbush Formation with pronounced angular unconformity. The apparent absence
of the Sardine Formation in this part of the Western Cascades indicates that the map area
may have been a highland in middle Miocene time or may have suffered extensive erosion
immediately prior to the deposition of Elk Lake lavas. Although basaltic lavas ann
pyroclastic rocks comprise most of the Elk Lake section in the southwestern part of the
quadrangle, the majority of the formation in the western and northern portions of the
map area consists of coarsely porphyritic andesitic flows and dacitic tuffs. A complex
of small intrusions, lahars, agglomerate, and bedded lapilli forms the rugged terrain
near Granite Peaks and was most likely the site of one or more late Miocene eruptive
centers.
In thin section, basalts from this unit contain abundant phenocrysts of olivine and
subordinate amounts of plagioclase and clinopyroxene. The mafic minerals are commonly
altered to iddingsite or serpentine, giving the rocks a dark-green color and making them
appear older and more weathered than less basic lavas of comparable aye. The andesites
are coarsely phyric and contain large phenocrysts of plagioclase and hypersthene and
9
a.
Scorpion Mountain lava flow (CT-8);
small plagioclase phenocryst in ground­
mass of p�gioc�se microlites, granular
pyroxene, and opaque oPe.
b.
Elk Lake Formation, andesitic flow
(CT- 59); phenocrysts of plagioclase,
hypersthene, and monoclinic pyroxene in
a matrix of black glass and fine crystals.
c.
Elk Lake Formation, dacitic Lava (CT28); amphibole, orthopyroxene, and plag­
d.
Outerson Formation, basaUic flow from
the base of the formation;
large olivine
crystals in ophitic groundmass of olivine,
plagioclase and optically continuous mono­
clinic pyroxene (CT-17).
ioc�se in finely crystalline groundmasc.
·-A
e.
Outerson Formation, basaltic andesite
flow (CT-68); corroded olivine and small
phenocrysts of plagioclase in groundmass
of plagioclase, two pyroxenes, and ore.
Figure 6.
f.
High Cascade lava ]low, middle Pleis­
tocene basaltic andesite; small olivine
phenocrysts in piZotaxitic groundmass of
plagioclase and two pyroxenes (CT-51).
A lZ
Photomicrographs of Lavas from the Breitenbush Hot Springs quadrangZe.
are at the same scale so that the height of each photo is equal to 1.6 mm.
10
.90
TH
•
.I0
•
0
•
0
01
8
+ .10
0
...
� .50
.,.
..
...
.so
0
0
6.
0
0
CA
so
Figur'e 7.
Sl
s2
'2
A p�ot of Si02 versus the 'I'O.t7:o FeO(tota�)/FeO(totalJ + MgO for samples fr-om
the Breitenbush Hot Springs quadrungle.
Analyses of Seor•pion Mount.a:in Za.vas
are indicated by filled circles, Elk Lake Fol'TTIQ.tion by triangles, Outerson
Formation by open circles, and High Cascade lavas by squares. Dashed line
separates field of tho�eiitic compositions (TH) from calc-alkaline compositions
(CAJ, after Miyashiro (1971).
subordinate amounts of cl i nopyroxene ± hornblende in a pilotaxitic groundmass of p l ag i o­
clase micro l i te s , two pyroxenes , and opaque ore ( Figure 6b). Hornblende i s commonly
ri nned with a fi ne-grained m ixture of pyroxene and ore minerals and may be completely
al tered to t h i s mater i a l i n some samples. In the dacitic dikes and sma l l stocks of the
Gra n i te Peaks compl ex , hornblende is the most abundant mafi c phenocryst and commonly
forms crystal s up to ha l f a centimeter l ong ( Figure 6c) .
K/Ar ages were obtained for a porphyritic E l k Lake flow near the contact wi th the
Breiten bush Formation and for a hornb 1 ende dacite dike that intrudes porphyritic 1 a vas
at the northern end of the Granite Peaks complex. These rocks yiel ded ages of 1 1 . 8 and
9 . 8 mil l i on years, respectively ( Appendix 1). Al though the basa l t i c fl ows in the
southwestern part of the map area were not dated for the present study , a basal t i c sil l
that crops out along Devi l s Creek just south of the map area was dated by Sutter (1978)
at 1 1 . 2 mil l i on years.
Outerson Formation
Dark-gray to light-gray basalts and basal t i c andesites of the Duterson Formation cap
Rhododendron Ridge and compri se most of the exposures i n the north-central parts of the
map area. Vents for these rocks have not been identified wi thin the Breitenbush Hot
Springs quadrangle; however, some lavas undoubted l y f l owed northward from the l arge
Pliocene shi eld vol cano that was active in the vicinity of Outerson Mountai n , about five
km southeast of the hot springs. Other l avas may have come from vents to the east whi c h
have s i nce been buried beneath the present H i gh Cascades.
Al though most l avas in the Outerson Formation are basal tic andesites, an unusual
sequence of basal tic fl ows and breccias crops out at the base of the formation i n areas
11
0
""
+
4
0
0
s0
S&
S2
60
Si02
Figui'e 8.
A pl,ot of S1:o2 tJeJ•sus tntnl rzlknli f!nntents for> samplBs of PliooP.nB and
Quaternary age from the Breitenbush Hot Springs quadrangle.
Analyses of
Plioaene samples are indioated by open ci1•cles, analyses of Quaternary lavas
by squares.
The dashed line separates field of alkaline compositions (ALK)
fJ•om subalkaline compositions (SUBALK), after Irvine and Baragar (1971).
north and south of Collawash Mountain (sec, 10, T. 9 S,, R. 7 E. ; sees. 33 and 34, T. 8
S., R. 7 E.).
These rocks contain abundant phenocrysts of olivine and display distinc­
tive groundmass textures in which small laths of plagioclase, granular olivine, and
opaque ore are enclosed in optically continuous plates of clinopyroxene (Figure 6d).
Basaltic andesites are also olivine phyric, but groundmass oliv1ne is replaced by
orthopyroxene, and the Lextures are COillllOnly intergranular rather than ophitic (Figure
6e). The relatively rare andesitic lavas contain phenocrysts of plagioclase and clino­
pyroxene, although even at these compositions, olivine may persist as corroded relicts
surrounded and embayed by orthopyroxene.
Chemical analyses of lavas from the Outerson Formation reveal that several flows
display the alkaline geochemical affinity noted by Naslund (1978) for lower Pliocene
lavas elsewhere in the Oregon Cascade Range. This feature can be seen in Figure 8, in
which the total alkali contents of all Pliocene and Quaternary samples from the map area
are plotted versus Si02
Two samples from the Outerson Formation display alkaline
affinities, one of which plots well within the alkaline geochemical field as defined by
Irvine and Baragar (1971) and is, in fact, nepheline normative. Both samples with
alkaline affinities are from flows that immediately overlie pre-Pliocene rocks. In
addition to their greater abundances of K20 and Na20, these lavas also display higher
values of Ti02, P205, and Ba than do other Pliocene-Pleistocene lavas with similar Si02
contents.
.
Six radiometric dates have been obtained for Outerson Formation lavas in the map
area, three of which were made for the present study. The ages cover a relatively
narrow range from 6.1 to 3.6 million years, even though an attempt was made to sample
all parts of the formation including flows just above the contact with Miocene rocks and
those immediately below High Cascade lavas.
High Cascade Lavas
Early High Cascade lavas overlap Pliocene and Miocene rocks in the basin east of
Hawk Mountain and along t he Clackamas River in the northern part of the map arP.a. They
12
yie l d K/Ar ages of one to two million years and include both no rmal ly and reversely
polarized flows. These lavas are in turn overlain in the southeas ter n and eas t - centr a l
parts of the quadrangle by the young flows and cones that comprise the High Cascade
platform . The topography in th i s area is dominated by the relative l y uneroded composite
cones of Ol all i e Butte, S i s i Butte, and the Pinhead Buttes , although many smaller cones
can also be iden tif i e d on the high plateau south and west o f Ola l l i e Lake. Because no
lavas having reversed remanent magneti s m have been found on t he Olall i e Lake plateau or
on any of the large cones , it i s l i kel y that they were erupted during the p resent ma g
neti c period and are therefore l ess than 660 ,000 yea r s old.
­
The early P l e i stocene High Ca s cade flows are dom i nan t l y composed of olivine -phyric
andesites w i th i n t e rgr anu l ar or di ktyta x i t i c textures . These l a vas are over­
l a i n by slightl y more siliceous basaltic andesites, many of whic h have pilotaxitic
b a s a l tic
textures (Figure 6f). The l ate Pleistocene l avas that make up the l arge cones or are
assoc i ated w i th the sma l l vents on the plateau of O l all i e Lake range i n compo s i t i o n from
bas a l tic andes i te to dacite and are generally more porphyritic than the o l der High
Cascade l avas . Samples f rom O l a l l i e and S i s i But tes conta i n abundant phenocrysts of
p l ag i oc l a s e u p to three mi l l imeters i n le ng t h .
�la f i c p henocrys t s i n these rocks include
cl i nopyroxene, corroded and jacke ted ol i v i ne , and sma l l crys ta l s of orthopyroxene.
Small p lugs of microdio r ite wi t h hypi diomor ph i c -gra nul a r textures are exposed at the
summits o f these volca noe s .
Andesitic and dacitic l avas were erupted from a n orthwest - tr endin g line of v ents
inc l ud e s Campbell Butte, Pyramid Butte, and Double Peaks . The most extens i ve of
these l avas forms a f l at-to p p ed ridge that extends for about three km northeast of
Brei tenbush L a ke and can be traced back to a comp l ex of dikes and small in t rusio n s on
the rounded knob between Ruddy Hill and Campbell Butte. In t h i n sec tion , these l avas
co n sis t of p l ag ioc l ase , o rtho py rox en e , amphibole , and minor amounts of cl i no py ro xen e in
an i n t erg ranu l ar groundmass of plagiocl ase, pyroxene, and opaque ore. Some specimens
have s mall crystals of ol ivine preserved within glomerocrysts of plagioclase and
pyroxene.
that
Fl ows , p l ugs , and bombs from the various cones and vents of l a t e P l e i s tocene age
were chemical l y anal yzed in order to asses s th e co mpo si t ional v a r i a t i ons w i t h i n a si n gle
volcano and between vol canoes of similar age . Analyses of five samples from the summit
and f l anks of Olallie Butte indicate that this volcano is composed of a s i ng l e geochem
i ca l l y related s u i te of lava s , i n contrast to the two or more suites commonly found in
the larger Cascade cone s . When l a vas from different ven t s a re com pa red , a t l ea s t two
s u i tes can be d i s ting u is hed on the basis of the i r trace- and mi nor- e l ement contents
( F i gure 9 ) .
All of the samples from O l al l ie Butte and two of the three samples from
Sisi B utt e have l ower contents of Ba and P 20 s , and higher ratios of K/Ba tha n other
young l avas at similar stages of d i f fere n t i a tion. The K/Ba ratio may be particul a rly
significant. Because it s h ou l d not b e affected by fra c tio n a ti o n of phen o crys t phases
fo un d i n these l avas , it may reflect compositional d ifferences betwee n " primi ti ve "
batches of magma. Although additional sam p l i n g and more complete analyses wou l d be
necessary for a th o roug h petrogenetic study, the availabl e data indicate that the s ma l l
and in t ermediate - s i z e cones of the Ol all ie Lake area , if ta ken together, have geochemical
trends s i mil ar to those seen in l a rge , mul tige net i c vo lcanoe s .
­
13
Ia
.2 5
lSO
0
0
.20
6
----
.1 5
•
.II
- -- - --
•
JOO
� -
--
•
0
•
0
zso
•
200
·I
·I
D . l.
D.l.
Figwoe
K/lh
21
•
24
• •
•
00
•
20
0
0
·I
0. 1.
14
9.
PLots o f P205 (wt. percent), Ba
(ppm), and the ratio K/Ba versus
a modified Larsen differentiation
index of ( 1/J Si + K - Cn - Mg)
for samples from cones and vents
aLong the High Cascade crest in
the Breitenbush Hot springs quad­
rangLe.
FiZ Zed circ les indicate
analyses of samples from OZaZZie
Butte, open circLes from Sisi
But.Le, half-fi l led tr-iangle from
Potatoe Butte, open tr>iangle from
TWin Peaks, square from West
Pinhead Butte.
Dashed lines sep­
arate geochemica lly distinative
suites.
DESCRIPTIONS OF STRUCTURES IN THE BREITENBUSH HOT SPRINGS QUADRANGLE
Rocks in the map area were folded and faulted during at l east three principal
episodes of tectonism : a mi ddl e or l ate Miocene episode that produced northeast-trending
folds and faults, a l ate Pl iocene and Quaternary epi sode of north-south faul ti ng , and a
Pliocene and Quaternary episode t�at produced northwest-trending faults. The northeast­
trending structures can be seen best in the bedded pyroclastic and epi c l as tic rocks of
the Brei tenbush Form a tio n. These 'o cks are asymmetrically folded into � broad upwarp
that extends into the western edge of the map area, where i t i s unconformably over l a i n
by l avas o f late Miocene and Pliocene age. Dips o n the northwestern limb o f this
structure reach 30° in the west-central part of the map area and as much as 60° i n
exposures near Detroit . A l though l avas o f the late Miocene E l k Lake Formation are not
folded, they are cut by northeast-trending faults that strike in approximately the same
direction as the major fold axis.
A second prominent structural trend is defined by several en eche l on normal faults
that strike in a north-northwesterly to northerly d i rection and are downthrown to the
east. These faults j u xtapose rocks o f �1iocene age against Pliocene l avas of the Outer­
son Formation at locations in the southwestern and northwestern parts of the map area .
An additional north-trending fau l t probabl y runs through the south-central part of the
quadr?nqle, where Pleistocene rocks along the North Fork of the Breitenbush River appear
to have been displ aced downward rel ative to the P l i ocene lavas that cap Bald Butte and
Bre1tenbush Mounta i n .
T h i s i nferred structure is a l so coinc ident with the promi nent
north-south l i neament formed by the Clackamas River and Cub Creek in the northern and
central parts of the map area . The cumul ative displacement across these faults is
greatest in the southern half of the quadrangle, where a throw of at l east 750 m ( - 2 ,500
feet) is ind icated by the strati graphic offsets.
A third and probably very young structural trend is indicated by the strong north­
westerly alignment of creeks i n most parts of the map area . Northwest-trending fa u l ts
can be identified in isolated outcrops where slickensides indicate smal l strike-slip or
obl ique-slip movements. The most prominent northwest-trending structure is one ind i cated
by the a l ignment of small streams and spri ngs i n the central part of the quadrangl e and
by fault surfaces and northwest-trending dikes l ocated in scattered outcrops along this
trend . The stratigraphic offset of Miocene and Pliocene rocks across this zone is
consistent with downward displ acement o f the northeastern side, probabl y combined wi th
a component of right- l a teral movement. Pl eistocene lavas have not been vertica l l y
offset by this fault but may have suffered some degree of lateral displ acement.
The structural grain in the Breitenbush Hot Springs area can be seen in Figure 10,
in which l ineaments drawn from high-altitude infrared photographs are presented along
with the l ocations of springs and young volcanic vents. The major l ineament trends
generall y correspond with the structural features observed on the ground ; northeasterly
trends are confined to the western part of the map area where rocks of Miocene and l ate
Ol igocene age are expose d , whereas northerly and northwesterly trends are most promi nent
in the eastern and central areas where o l der rocks a re covered by l avas of Pl iocene and
Quaternary age. North- and northwest-trending l i neaments are also defined by the
a l ignments of springs in the central part of the map area and by the l ocations of cones
and sma l l vents a l ong the High Cascade crest.
15
0
I
_
t
/
.6
/
I
I
1
\
I
�
---oo
0
----.£
r
I
�I
I
I
I
I
�
0
A
"
1\
i_
�I
A
A
\
I
l! "'-...
A
A
I
I
I
.......
0
0
I
\
10
1
I
I
I
\&
..
\
0
..
..
..
-
A
..
I
..
v
A
A
.6
..
1 2 1° 4 5 1
M I LE S
0
FigUI'e 10.
N
5
t
Lineament map d.roJ..m from high-altitude infrared phowgraphs of the Breiten­
bush Hot Springs quadrungZe. A lso shoum are the locations of ynuYI.tJ PoZcanic
vents (tPinYI.tJZe.s), hot springs (fi lled circles), and ooZd springs (open
cirocZes) .
16
REFERENCES
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actions of the Lunar Geological Field Conference , Bend , Oregon , August 1 96 5 : State
of Oregon Dept. of Geol ogy and Mineral Indu s . , 98 p .
Cal l aghan, E . , 1 933 , Some features of the vol canic sequence in the Cascade Range i n Oregon :
Am .
Geophy s . Union Trans . 1 4th Ann. �1tg . , p . 243-249.
Davie , E . I . , 1980, The geology and petrology of Three Fingered Jac k , a High Cascade
volcano in central Oregon : Eugene , Oreg . , Univers i ty o f Oregon maste r ' s thes i s ,
1 38 p .
Halllnond , P . E . , 1 97 9 , A tectonic model for evo l u tion of the Cascade Range , in Cenozoic
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tol og i sts and Mineral ogist s , 335 p .
Hanlnond , P . E . , Anderson , J . L . , and Mann i n g , K . J . , 1 980, Guide to the geo 1 ogy of the
upper C l ackamas and North Santiam Rivers area , northern Oregon Cascade Range, in
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Dept. of Geology and Mineral Indus . Bul l et in 101 , p . 133-1 6 7 .
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colllno n vol canic rock s : Can . Jour. Earth Sci . , v . 8 , p . 523-548.
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Maynard . L . C
1974 , Geology o f Mt . Mclaughl in :
master ' s thesis , 1 3 9 p .
. •
Eugene , Oreg . , Unive rs ity of Oregon
�1cBirney, A . R . , 1 968, Petrochemistry of the Cascade andesite volcanoes , in Andesite
Conference guidebook: State of Oregon Dept . of Geology and Mineral Indu s . Bul l etin
62 ' p . 1 01 -1 07 .
McBirney , A. R . , Sutter, J. F . , Nas l un d, H. R . , Sutton, K . G . , and White, C . �1. .
Epi sodic volcanism in the central Oregon Cascade Range : Geology, v . 2 , p .
1 974 ,
585-589.
Miyashiro, A . , 1 97 4 , Vol ca n i c rock series in isl and arcs and active continental margins :
Am . Jour. Sci . , v . 274, p . 3 2 1 - 3 5 5 .
Na sl und, H . R . , 1 97 8 . The geology of the Hyatt Reservoir and Surveyor Mountain quadrangl e s ,
Oregon : Eugene, Oreg . , University o f Oregon master ' s thesis , 126 p .
Peck, D . L . , Griggs , A . B . , Schl icker, H . G . , and Dol e , H . H . , 1 964 , Geol ogy of the
central and northern parts of the Western Cascade Range in Orego n : U . S . Geological
Survey Professional Paper 4 4 9 , 56 p .
R i nqwood , A . E . ,
London , v .
1 974 , The petrological
1 30 , p. 1 93-204.
Sutter, J. F . ,
K/Ar ages of Cenozoic vol canic rocks from the Oregon Cascades west of
I s ochron/Wes t , no. 21 , p. 1 5-21 .
1 2 1 ° 30 ' :
evol ution o f isl and arc systems :
J . Geol . Soc.
1 978,
Sutton , K . G . , 1974 , Geology of Mt . Jefferson :
maste r ' s thesis , 1 1 2 p .
17
Eugene, Or�g . , Uni versity of Oregon
Tayl or , E . M . , 1 97 8 , Fie l d geology of S . W . Broken Top quadrangl e , Oregon :
Dept. of Geology and :11neral Indu s . Special Paper 2 , 50 p.
State of Oregon
'
Taylor, E . M . , 1 980, Vol ca n i c and vo l c a n i c l a s t i c rocks on the east f l a n k of the central
Cascade Range to the Deschutes R i ve r , Oregon , in Geolog i c\ fiel d trips i n western
Oregor and southwestern Wash i n g ton :
State of Oregon Dep t . of Geology and Mineral
Indus\ Bul l etin 1 01 , P . 1 -8 .
Thayer, T . P . , 1 93 7 , P etro l ogy o f l a ter Tertiary and Quaternar y rocks of the north-central
Cascade t1ountains in Oregon :
Geol. Soc. Am. Bu l l . , v . 48 , p . 1 6 1 1 - 1 651 .
Thayer, T. P . , 1 93 9 , Geol ogy of the Salem H i l l s and the North S a n t i a m R i v e r bas i n , Oreg on :
S tate of Oreg on Dept. of Geology and Mineral I ndus. Bu l l etin 1 5 , 40 p .
Whi te , C. M . , 1 980 , Geol ogy and geochemi s t ry of Mt . Hood Volcano:
of Geology and Mineral Indus. Special Paper 8 , 26 p.
White, C . t1. and
McBirney, A. R., 1 97 g ,
State of Oregon Dept.
S ome qua n t i ta t i ve aspects of orogenic v o l c a n i s m
tecto n i c s and regional geophy s i c s of th e
i n the Oregon Cascades, i n Cenozoic
Western Cordil l era :
W il l ia m s , H . , 1 954 ,
Petrography:
Geo1 .
Soc. Am. Memoir 1 52 , 388
p.
Igneous rocks, in W i l l iams, H . , Turner, F . J . , and Gilbert, C . M . ,
San Francisco, Cal if . , W . H . Freeman and Co. , p. 3-1 57 .
18
APPENDIX I
K/Ar AGES OF SAMPLES FROM THE BREITENBUSH HOT SPRINGS QUADRANGLE
Newly Acqui red Ages ( th i s report )
Ana l ys i s No.
(Appendi x I I )
F i e l d No.
%K
%Ar
40
rad
Age ( M . Y . )
1.
52
CT-51
0 . 63
10
1 . 02 ± 0 . 1 4
2.
46
CT-32
1 . 00
20
1 . 07 ± 0 . 08
±
3.
42
CT-75
0 . 70
11
1 . 49
4.
40
CT-52
0 . 86
18
1 . 62 ± 0 . 1 4
5.
43
CT-22
0 . 64
10
1. 97
i
0. 27
:t
0.17
0 . 09*
6.
32
CT-41
2.17
41
4 . 04
7.
22
CT-68
0 . 78
42
4 . 74 ± 0 . 1 9
8.
18
CT- 1 7
0 . 44
29
6 . 05
16
CT-64
0 . 897
34
9 . 83 ± 0 . 4 6
9.
±
0 . 31
10.
9
CT-59
1 . 25
66
1 1 .8
± 0.4
11.
5
CT-14
2 . 08
22
19.4
± 0 . 4*
2
CT- 8
1 . 291
88
25.5
:!::
29
CT-62
1 . 063
11
0 . 8**
1 . 59 ± 0 . 2 1 **
Note: Ages fol l owed by ( * ) were determined at the K/Ar l a boratory at Oregon
State University; al l others were determined at the Department of Geology and
Geophy s i c s , Uni vers i ty of Utah.
Addendum: Ages fol l owed by ( ** ) were recei ved after th i s report was prepared .
Previously Pub l i shed Ages
F i e l d No.
Rock Type
Source
Age ( M . Y . )
:!::
12.
DMS-47
Basal tic andes i te (wr)
Sutter ( 1 978)
3 . 60
13.
PH l D
Tephra ( pl a g )
Hammond and
others ( 1 980)
4 . 20 ± 0 . 30
14.
DMS-48
Basa l t i c andesite (wr)
Sutter ( 1 978)
4 . 72 ± 0 . 1 9
15.
DMS-43
Ash flow ( p l a g )
Sutter ( 1 978)
19.7
16.
PEH-77-8
Ash flow ( pl a g )
Hammond and
others ( 1 980)
23 . 2 ± 0 . 8
24 . 3 :!:: l . 1
t
0 . 05
0.2
Note: (wr) i nd i cates whole-rock age, ( p l a g ) i nd i ca tes dated plagiocl ase
separate.
19
II
APPENDIX
CHEMICAL ANALYSES O F SAMPLES FROM THE BRE I TENBUSH HOT SPRINGS QUADRANGLE
BRE ITENBUSH
FORMATION
SC.ORPTON MOUNTAIN LAVAS
ELK LAKE FORMATION
1
2
3
4
5
6
7
B
9
Si0
2
Ti0
2
65.91
53.16
55.20
56.25
55.20
6 3 . 46
48.64
58.00
58.80
.40
1.87
1.26
1 . 29
1.27
.56
1.17
.93
.92
i>J. °
2 3
12.70
15.36
16.52
16.74
15.24
13.57
16.34
17.52
1 7. 29
3.40
3 .83
4.85
4.03
2.34
8.19
3.41
3 . 52
6 . 72
6.24
3 . 95
4.34
3.32
1 . 39
2.47
2.59
Fr!.
P3
Fr!.O
�no
3.35
rxl
��0
.08
.16
.19
.13
.19
.13
.13
.10
.09
.]7
3.57
2.54
1.99
1.42
. 79
6 . 54
3.44
3 . 41
6.00
2.96
7.25
5.87
G. 79
5.45
3.19
9.45
7.08
3.00
3.26
4.23
3 . 76
).46
3.61
3.41
4.02
3.97
t'la
K0
2.0 3
1.56
1 . 34
1 . 84
2.49
2.97
1 . 32
1.15
1 . 29
.OG
.32
.48
.37
.45
.10
.42
.13
.17
H20
8.46
1.66
1 . 74
2 .1 4
5.50
5 . 27
2.40
1.46
1.44
cao
0
2
2
PPs
'It>ta1
Ba
9
9 . 32
nd
98.29
RJ
72
52
Sr
152
3 24
a:
Ni
nd
rxl
99.44
63 7
409
365
34
33
99 . 31
951
830
75
57
tr
6
77
99.04
100.10
67
4
486
6
33
99.40
690
9 . 71
9
93
15
27
30
231
1222
483
548
tr
tr
tr
250
65
34
&
6
tr
123
43
J3
C U< LAKE FOR'IATIOO
10
11
60.50
12
61.1 5
14
13
61.72
61.54
15
62.88
16
63.27
17
63.69
Si0
2
Ti0
2
59.20
.83
.88
. 90
.61
.76
.73
Al 0
2 3
Fr!. °
2 3
1 7 . 68
16.84
16 . 9 3
17.52
16 . 1 3
16.74
2.41
2 . 33
3.52
3 . 28
2.90
2. 35
2 .19
3.56
2.40
2.63
2.50
3.11
2. 74
.10
.09
. 07
2. 37
l . 41
3.16
.11
.08
.07
.09
2.85
3.31
2.23
2.47
3.01
2 . 46
2. 36
6 . 61
6. 4 7
1 . 89
. 07
5.24
Fr!.O
�no
1·�0
cao
Nap
K20
PPs
HP
'It>till
.65
1 � . 74
.65
l�.R4
5.84
5.40
5.49
5.44
3.64
5. 76
3.46
4.07
4 . 41
3.96
3.95
4. 34
4 .1 2
1.0 7
1.16
1.37
1 . 08
1 . 53
1 . 31
1.08
1 . 42
.13
.11
.11
.14
.76
---.!..:2!
1.84
99.73
100.13
100.19
289
284
1 .67
99.17
.1 7
.09
.11
.lJ
�
_..b.l.i
�
1.18
99.23
100.53
271
99.43
198
99.65
34 5
Ba
256
Fb
20
24
31
26
37
32
16
31
Sr
501
494
437
431
452
768
911
339
a:
29
17
20
14
54
16
15
31
25
18
12
44
33
38
15
Ni
31
242
99 . 56
305
280
333
20
APPEND I X I I
( continued )
ot1l'ERSCtl FORiATIOO
18
Si0
2
Ti0
2
A1
3
p
19
20
23
22
21
24
25
26
47.73
47.99
48. 70
52.08
53.16
53.16
54.05
. 94
.76
1 . 40
56.40
1 . 43
1.19
1.29
1 .07
1 . 09
16.34
16.57
15.47
17.28
17.57
16.62
16. 59
17.34
16.82
55.60
34
l.
Aa 0
2 3
3.99
3.32
3.25
5.84
3.52
3. 40
2 . 43
2.31
3 . 78
flaO
6. 94
6.12
5. 74
3.23
4 . 29
5.54
5 . 31
4.91
lltlO
4 . 26
.16
.17
.15
.13
.12
.15
.14
.12
7.46
8.55
8.49
4. 52
5.59
5. 02
5.83
5.40
3.47
9. 05
11.82
11.12
8.21
8.45
8.00
8. 54
7.83
7.09
3.61
2.60
2.41
3 . 81
3.53
3.86
3.34
4 .08
3. 84
93
.OS
.03
1 . 29
.83
.99
.86
.76
1.34
57
.28
�
.67
�1;10
CaO
re o
2
K0
2
P 0
2 5
H 0
2
'lt>ta1
Ba
.
.26
.10
.09
. 59
.38
1.14
1 .15
3.20
1.33
�
99. 04
99. 33
75
245
99.41
99 . 71
99.16
99 . 56
398
1131
134
.
436
99.11
340
.
. 21
27
�
100.67
303
10
.
1 . 72
99.57
356
36
lb
7
4
3
10
13
14
12
11
Sr
430
249
217
1151
1176
847
774
950
739
Ni
141
cr
189
268
303
43
114
94
112
102
68
137
145
46
83
77
87
102
35
� FO!lMATIGI
27
28
29
30
31
32
Si0
2
Ti02
57. 29
56.80
56.60
57.08
57.50
1.16
1 .09
1 . 20
.75
1 . 25
Al 0
2 3
17.29
16.93
17 .5 5
1 . 02
16.89
17.69
15.50
2 .61
2.05
2. 29
3.16
3.14
3. 57
5.38
5.14
4.87
4. 00
4. 02
4. 05
fla p
)
flaO
lltlO
CaO
re o
2
K 0
2
P 0
2 5
H 0
2
1btal
62.31
.12
.12
.10
.10
.11
7 . 21
7.34
6. 75
7.21
7.02
4.56
11
.
3 . 95
4 . 06
4.11
3.52
3.13
4 . 37
1 . 27
. 89
1 . 25
1 . 06
.48
2 . 53
.37
.28
.27
.12
.16
. 34
�
�
�
1 . 03
1 . 34
�
99.40
99 . 04
99.28
99.38
101.22
100.58
Ba
468
348
391
286
It>
282
13
17
19
15
�r
24
61
456
617
747
612
831
340
cr
10
1 00
25
281
51
tr
Ni
48
51
35
81
51
21
636
7
APPENDIX I I ( continued)
HI Q! CAS0J:£.
33
34
35
37
36
38
39
40
41
51.96
52.39
53.70
53.04
53.70
53.04
52.08
53.33
53.04
17.63
18.56
18.81
18.53
18.99
19.09
18.54
16.97
18.87
FeO
4 . 79
6.14
5.34
4.45
5.42
3.23
4.10
5.21
5.15
cao
8.00
8.88
8.40
8.88
8.73
8.89
8.05
8.45
.67
.65
.68
.66
70
.57
.75
.93
Si0
2
'1'10
2
t.J..p3
Fe
P3
l'hO
Na 0
2
.91
3.66
.12
3.47
K
P
p °
2 5
H
P
'lbta1
Ba
�
1.10
1.59
.12
3.66
. 21
1.44
99.73
303
2.43
.12
3.88
.89
.99
2.34
3.27
.ll
.ll
3. 77
4 .00
•
.11
.18
.17
.11
99.36
99.73
99.23
99 . 80
.94
217
.73
.16
.75
219
242
7
8
1.08
8
3.86
.10
3.52
.16
2. 21
-99.79
.21
2.04
99.73
3.82
.61
.26
. 21
100.24
99.43
.73
.56
657
79!1
no
130
75
736
1071
791
Ni
191
37
26
28
23
33
45
3.6 5
.11
8 . 77
271
720
26
3.65
.14
2.77
380
723
49
.11
3.01
.89
314
10
10
620
264
3.88
1.27
222
�'r
cr
1.01
224
9
7
1.10
113
56
44
9
7
149
116
74
HIQ! CAS0J:£.
42
43
44
46
45
47
48
49
50
Sio2
53.75
53.54
53.70
53.52
54.58
54.90
55.20
55.60
55.00
Al20)
17.40
17.90
17.91
16.44
17.80
17.17
17.94
18.07
17.13
5.62
4. 79
5.72
5.32
3.18
5.11
6.12
4.50
1.10
5.04
4. 23
5.65
4.92
4.27
4.86
4.38
4.73
4.00
3.93
3.85
4.09
3.80
4.05
3 . 56
.19
.23
99.92
100 .54
'l'i02
Fe 203
�'eO
1-t\0
�0
cao
1.20
3.17
.14
4.80
.86
2.84
.12
1.25
2 . 74
.13
7.91
8.69
6.87
K20
.90
.70
1.06
H20
1.12
--
.96
--
1.39
0
2
3. 70
P205
.46
Na
'lbta1
100.17
3.77
.24
99.45
99.47
Ba
369
31 6
&
675
659
550
84
58
cr
Ni
14
75
66
11
128
14
73
1.19
2.91
4.00
.10
.14
7.32
8.07
1.19
2.93
.11
�
.32
--
.44
98.59
99.44
.12
.70
1.14
.26
1.58
7.90
1.17
.36
.88
7.51
.73
.47
2
4 1
R:>
1.2 9
.43
99.32
.63
268
538
416
297
545
1461
758
159
88
71
9
188
9
103
22
14
78
1.11
3.44
.12
7.56
.78
.70
1.06
6.96
.13
7.56
.64
.24
1.03
99.14
345
319
944
625
751
83
69
72
9
53
10
38
10
67
APPENDIX I I (continued)
HIGl CA'iCA!JE
52
51
53
54
55.60
55
57.00
57.09
60 . 00
.81
1 .09
.94
.82
.56
18.05
17.97
17.34
18.26
16.32
3.40
2.22
2.52
3.53
3.22
4.36
4 . 70
2.97
.76
,10
.12
,10
.09
3.57
4.04
3.12
1.39
56.00
55.30
Al .PJ
1 .1 5
17.23
.97
1 . 11
17.81
18.06
�
5.68
5.31
3.89
r-tlO
M;JO
.13
.12
4.19
4.55
0.0
7.17
0
2
7. 4 8
7.96
a. s1
Na
3.98
3. 78
4
3.96
1.07
.1\6
•
PPs
.44
.25
.18
.87
'il;ltoil1
.60
.34
.5 2
100.32
99.21
99.16
99.99
8a
469
380
275
312
289
362
ltl
13
9
9
7
16
Sr
592
798
1037
1 173
9
105
149
33
59
130
26
2 .68
�2°3
Kp
H20
Cr
Ni
2.11
2 .91
,10
3. 8 5
. 37
3.32
.u
3.93
79
S10
2
Ti0
2
N.. 2°3
Fe203
39
53
3 .88
73
.R2
3.84
.25
.19
.21
.05
.20
.52
--
.52
100.72
100.05
•
.35
99.98
.'ll
-.56
99.92
6.51
.'ll\
4.59
] . 74
260
12
1035
702
634
36
34
73
53
35
26
59
30
STJ\Ntii\RD !lOCKS
9
AMii-1 *
/PMH-1)
ws-1+
('IMS-1)
55.58
58.09
59.80
60.27
60.00
.97
1 . 03
.91
.79
.83
.17
. 13
1 7 . 43
18.87
18.58
17.44
17.14
17.48
17.92
8.55
8.17
7.16
6.49
6.36
6.15
5. 31
18.35
.14
.11
.10
.09
.09
.10
.22
3.99
4.96
3.78
2.97
3.11
3.06
.17
.29
6.83
7 . 94
8.06
6.23
6.02
6.07
1.48
1 .27
4.37
1.22
4.11
9.07
8.82
1.31
1 .25
4.14
.18
.11
4.23
.1 2
--
�
1 . 27
1 . 21
M;JO
cao
Na20
3 . 97
4.00
3.65
KP
1.10
.69
.so
.44
.28
.19
.21
H 0
2
'll;lta1
1 . 39
2.04
.34
1. 4 4
.97
99.87
100.67
99.99
99.15
99.76
l'bte :
(AMH-1 )
P205
Mt , ltlOd
+ Marys
). 73
7.65
4.14
52.99
54.79
f>tlO
*
66.93
8.17
OOPLICATE ANALYSES BY XRF
44
58
56.48
Sio
2
Ti02
57
56
oilnd ('IMS-1) are
Mdesite
oilverages
of
Peak Syenite
23
4.14
.39
99.89
100.05
r:ultip1e analyses by XRF.
59.48
5 . 20
.19
.16
99.39
APPENDIX I I I
LOCATIONS OF ANALYZED SAMPLES
( Roads and section , town s h i p , and range l ocati ons are those of U . S . Forest
Service Map of Mt. Hood National Forest, revised edi t ion 1 97 9 . The map i s
ava i l able from the Mt. Hood National Forest Headquarters , 1 9559 S . E . D i v i s i on ,
Gresham, OR 97030; or the U . S . Forest Service Regional Off i c e , 3 1 9 S . W . P in e,
Portland (ma i l i ng address: P . O . Box 3623, Portland, OR 97208 ) .
1 .
i n road
9 S , R 7 E.
( B X - 1 0 2 ) Rhyod a c i t i c ignimbrite
g ro u nd , center, sec 1 9 ,
T
cut on
RS46
a t C l eator Bend camp­
2.
(CT-8) Basal t i c andesite flow i n road c u t o n S760C, west-central edge,
sec 29, T 8 S , R 7 E .
3.
(CT- 1 5) Basal tic andesite d i ke i n road c u t on 040, east-central edge,
sec 1 8 , T 9 S, R 7 E .
4.
(CT-25) Basal t i c andesite flow on r i dge between Scorpion Mounta i n and
Mansfi eld Mou n ta i n , 4500' el evation, SW �. sec 5 , T 8 S, R 7 E .
5.
(CT- 1 4 ) Thi n andes i t i c flow i n road c u t o n 030 , SW � . sec 9 , T 9 S , R 7 E .
6.
(CT-57) Daci t i c f l ow i111n ediately beneath flow o f sampl e 5 .
7.
(CT- 1 3 ) Basa l t i c flow i n road cut on 4685, NE � . sec 2 7 , T 9 S , R 7 E .
8.
(CT-58) Andes i t i c f l o w i n road c u t on S760, SW � , SE � .
R 7 E.
9.
sec
2 9 , T 8 S,
(CT-59) Andes i t i c f l ow i n road cut on S760, 0 . 1 mi north o f sample 8 ,
S E � . sec 2 9 , T 8 S , R 7 E .
eastern edge,
10.
(CT-65) An d e s i t i c bomb i n a g gl u t i n a te on Granite Peaks
el evati o n , north-central edge, sec 7, T 7 S , R 7 E .
11.
(CT-67) Andes i t i c flow in road cut on S70 1 C , NE �. SE �. sec 3 2 , T 7 S ,
R 7 E.
12.
( CT-69) Andes i ti c
R 7 E.
13.
( CT-28) Stock o f hornblende andesite i n
sec 1 8 , T 7 S , R 7 E .
14.
(CT-63) Dac i ti c f l ow i n road cut on S635A, center of northern �. sec 5 ,
T 7 S, R 7 E.
15.
( CT-30) Dac i ti c f l ow i n road
16.
( CT-64) Di ke o f
T 6 S , R 7 E.
17.
( CT-61 ) S i l l o f hornbl ende dac i te i n road cut on 570 1 0 , NW �. sec 20 , T 7 S ,
R 7 E.
18.
( CT- 1 7 ) Basa l t i c f l ow i n road cut on 4688. SE � . NW � . sec 1 0 , T 9 S , R 7
19.
( CT-54) Basa l t i c f l ow i n road c u t on S701 , south-central edge, s e c 3 4 ,
T 8 S, R 7 E.
20.
(CT-21 )
Basa l t i c
fl ow i n
road cut on S701 C ,
hornblende
f l ow in
cut
sma l l
�.
sw
4960'
� . sec 28 , T 8 S ,
quarry on road S70 1 B , N E �.
on S701 C , SW � .
dac i te i n road
road cut
NW
ridge,
cut o n
sec
4, T 8 S, R 7 E.
S635A, S E � . SW � . sec 32,
on S760N , center, sec 33, T 8 S, R 7
24
E.
E.
21 .
(CT-36) Basal t i c f l ow i n road cut on 5650, NW � . SE � . sec 8 ,
22.
(CT-68) Basal t i c andesite f low exposed on c l i ff face at Gyp P oin t , 4960'
e l evat i o n , south-central part, sec 21 , T 8 S , R 7 E.
23.
( CT-55) Basa l t i c andesite flow exposed on c l i ff face at Bal d Butte, 4800 '
elevat i o n , NW � . sec 1 2 , T 9 S , R 7 E .
24.
( CT-66) Basa l t i c andesite f l ow exposed in cl i ff face just east of Bob
Meadow , 4000' el evation, SE �. sec 20 , T 7 S , R 7 E .
25.
(CT-56) Basa l t i c andesite flow in road cut on RS46, SE � . SE �. sec 1 2 ,
T 9 S , R 7 E.
26 .
( CT- 34 ) Basa l t i c andesite flow i n road cut on RS46 , NW � . SE � . SW � .
sec 6 , T 7 S , R 8 E .
27.
( CT-37) Basal t i c andesite flow in road cut on $650, south-central edge,
sec 4 , T 7 S , R 8 E .
28.
(CT-53) Basal t i c andesite flow i n road cut on 5701 , center, sec 2 7 , T 8 S ,
R 7 E.
29.
( CT-62) Basa l t i c andesite fl ow i n road cut on $652, NE �. NE �. sec 3 ,
T 7 S, R 7 E.
30.
(CT-24 ) Basa l t i c andesite d i ke i n road cut on 5756 , north-central edge,
NW �. sec 2 5 , T & S , R 7 E .
31 .
(CT-20) Andes i t i c f l ow i n road-rock quarry on 5701 , NW � . NW � . sec 1 5 ,
T 8 S, R 7 E.
32.
( CT-4 1 ) Andes i ti c f l ow i n road c u t on S707 , center, s ec 21 , T 7 S, R 8 E.
33.
(CT-39) Basa l t i c f l ow i n road c u t on 57 07 , SE � . S E � . sec 21 ,
R 8 E.
34 .
( CT-7) Basa l t i c flow i n outcrop a t northwestern base of Olal l i e Butte,
4800' e l evati o n , NW �. NE �. sec 36, T 8 S , R 8 E .
35.
( CT-6) Basa l t i c andesite flow in outcrop a l ong Ol a l l i e Butte trai l ,
5 1 20 ' e l evat i o n , central part, E �. sec 3 6, T 8 S , R 8 E .
36 .
( CT-5) Basa l t i c andesite flow i n outcrop a l ong Ol a l l i e Butte trai l , 5280'
elevation, south-central part, sec 36 , T 8 S , R 8 E.
37.
( CT- 3 ) Basal t i c andes i te f l ow in outcrop near the summit of Ol a l l ie Butte,
6900 ' e l evati o n , NW �. NW �. sec 2, T 9 S, R St E .
38.
(CT-4) Basal t i c andesite bomb from bedded c i nders north of the summi t of
O l a l l ie Butte, 6750 ' e l evation , NW � . NW � . sec 2 , T 9 S , R � E.
39.
(CT-42) Basal t i c andesite flow in road cut on RS46, north-central edge,
SE � . sec 1 3 , T 7 5 , R 7 E .
40.
( CT-52) Basal Lic andesiLe flow i n road cut on 5737 , north-central edge,
sec 24 , T 8 S, R 7 E .
25
T
T
7 S, R 7 E.
7 S,
41 .
( CT-2) Basa l t i c andesi te fl ow i n outcrop northwest of Ola l l i e Lake, 5 100'
elevation, north-central part, sec 1 1 , T 9 S, R 8 E .
42.
( CT-75} Basal t i c andesite f l ow in outcrop at head of canyon a l ong the North
Fork of the Brei tenbush R i ver, 3280 ' e l evati on , SW t , sec 21 , T 9 S , R 8 E .
43.
(CT-22) Basal tic andesite flow in road cut on 5756 , 5E
R 7 E.
44.
( CT-1 ) Basal t i c andes i te flow i n outcrop west of Top L a k e, 5100 ' e l evation,
SE % , sec 1 0 , T 9 S, R 8 E .
45.
(CT-33) Basal t i c andesi te f low i n road cut o n RS46, west-central edge, sec 7 ,
T 7 S , R 8 E.
46 .
( CT-32 ) Basal t i c andesi te f l ow i n road cut on 5806, NW t, 5E t, sec 1 8 ,
T 8 S, R 8 E.
47.
( CT-47) Basa l t i c andesi te flow in outcrop north of Fis h Lake , 4480' eleva t ion ,
center, s e c 3 4 , T 8 S , R 8 E .
48.
(CT-70) Basa l t i c andesite f l ow in outcrop east
tion , center, sec 25, T 8 S , R 7 E .
49.
(CT- 1 0 ) Basal t i c andes i te flow or sma l l i ntrusion , rubbly outcrop at summ i t
o f West P i n head Butte , 5500' elevation, north-central edge, sec 26 , T 7 5 ,
R 8 E.
50 .
(CT-45) Basal t i c andesite c i nders . summit of Potatoe Butte, 5280' e l evat ion ,
SE t, NW t , s e c 4 , T 9 S , R 8 E .
51 .
( CT-44) Basal t i c andesite f l ow i n road
center, sec 1 1 , T 9 S , R 8 E .
52.
( CT-51 ) Basal tic andes i te flow in road c u t on 5 7 3 7 , SE t . sec 2 4, T 8 S ,
R 7 E.
53.
(CT-48) Basa l t i c andesi te flow i n outcrop on west summ i t of S i s i Butte,
5600 ' elevatio n , north-central edge, sec 9, T 8 S, R 8 E .
54 .
( CT-50) Basal t i c andesite d i ke i n outcrop between summi ts of S i s i Butte,
5440' elevation, north-central edge, sec 9, T 8 5 , R 8 E .
55.
(CT-49) P l ug of mi cro-d iorite, east summit of Sisi Butte , 5600' elevat i on ,
south-central edge, sec 4 , T 8 S , R 8 E .
56.
(CT-46) Basa l ti c andesite flow i n road cut on 5829, SE t , sec 2 g , T 8 S,
R 8 5.
57.
(CT-43) Hornblende andesite flow i n road cut
NE t , 5W t , sec 24 , T 9 S, R 8 E .
58.
( S- 1 50) Oac i t i c flow in outcrop at Double Peaks , sec 9, T 9 S, R 8 E ;
analys i s reported by Thayer ( 1 937 ) .
26
cut
of
t,
sec 1 3 , T 7 5 ,
Berry Creek , 3100' eleva­
on S42 west of Ol l a l l i e Lake,
on
S42 north of Gi bson Lake,
ST A T E
D E PA R T M E N T O F
DONALD
G E O LO G Y
A.
SPECIAL
O F O REGON
AND
M I N E RAL
H U L L , ST A T E
I N D U ST R I E S
PAPER 9
G E O LO G I C
G E O L O G IST
of
t he
B R E IT E N B US H
MAP
S PR I NG S
HOT
Q UA D RA N G LE ,
O REGO N
1980
T][ME
15
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24
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0
N
Q u a ternary a l l u v i um :
Unconso lidated deposits of bou lders
grave l, and sand in the flood p lains of the Breitenbush
and Clackamas Rivers
H i g h C a s c a d e l a v a s , ·ba s a l t a n d ba s a l t i c a n d e s i te :
Flows,
breccia, and sma l l intrusions of o livine basalt and
o livine-pyroxene basa l tic andesite; latera l ly extensive
flows erupted from shie ld vo lcanoes or fissures make up
most of the sec tion; sma l l- and intermediate-size
composite cones are abundant in the upper part of this
unit in the southeastern and east-central parts of the
map area
H i g h C a s c a de l a v a s , a n d e s i te a n d d a c i te :
Flows and sma l l
intrusions of hornb lende-pyroxene andesite and dacite;
lavas were erupted onto o lder High Cascade basalts and
basa ltic andesites from severa l vents located south and
west of Olal lie Lake
O u te r s o n Forma t i o n :
Flows, breccia, lapi l li tuff, and
sma l l intrusions; basa l tic flows having distinctive
ophitic textures and containing groundmass o livine crop
out at the base of the Outerson Formation near Co l lawash
Mountain; most lavas in this unit are o livine-pyroxene
basa l tic andesite with intergranu lar or dikty taxi tic
textures; subordinate vo lumes of andesite crop out in
the northeas tern part of the map area
E l k L a ke Forma t i o n :
Flows, lapi l li tuff, and intrusive
rocks; weathered, o livine-bearing, basa ltic flows and
bedded lapi l l i crop out in the southern part of the map
area; coars e ly porphyritic, hornb lende-pyroxene andesite
over lies rocks of the Breitenbush Formation in the
western part of the map area; hornb lende-bearing, dacitic
flows, tuff, and sma l l intrusions form the rugged ter­
rain around Granite Peaks, in the northwestern part of
the map area
S c or p i o n Mo u n ta i n l a v a s :
F lows and subordinate amounts of
breccia and lapi l li tuff; dark- gray, aphyric flows of
tho l eiitic basa ltic andesite and andesite cap Scorpion
Mountain and are exposed in iso lated outcrops a long the
western edge of the map area; Scorpion Mountain lavas
appear to be interca lated with tuffs and tuffaceous
s ediments in the upper part of the Brei tenbush Forma tion
B r e i ten b u s h Forma t i o n :
Ash flows, tuff, vo lcanic breccia
and sands tone, and subordina te lava flows; l ight-gray
and pa le-green ash flows with rhyodacitic composi tions
crop out a long the Breitenbush and Co l lawas h Rivers in
the southwestern and west-centra l parts of the map area;
andesitic to dacitic vo lcanic breccias are exposed in
iso lated outcrops; white or pa le- pink tuff and tufface­
ous sandstone occurs at the top of the unit
GEOLOGIC SYMBOLS
CONTACTS
�ifJ;����:{."5&000•
�p="l:./-'.U"'"-"'-"'=
- "--'-"-'-.LC-"'-i'-W.+"l�..la="""'"'"'' J 44 . 45 '
1 2 1 . 45'
1 6 73 II/
Base Ma p by U . S . G eo l og i c a l S urvey
Topography b:t photogra mmetnc methods from aenal
1949 a n d 1958
Polycon1c prOJectiOn
Fteld checked b)' USGS
1961
1927 N or t h Amertcan d a t u m
1 0,000 foot g n d based on Oregon coord 1 n a t e system, n o r t h zone
1 000 met@r Umversal Transverse Mercator gnd t t c ks,
zone 10
'98"""" E
l 62 500
*
, .. I
I. .
Control b11 USGS and USC&GS
photographs taken
SCALE
.���;V".
'i
ROAD CLASSIFICATION
'•
, •.
""'
Untm proved dtrt .. ,. , .. .. .. .. ,
[:J
C O N TO U R I N T E R VAL 80 FEET
DATUM I S M EA N S E A LEVEL
UT"' GRIO "liD 196\ "'"'GNE!IC NORIIi
Where omt tted, l a n d lmes have not been established
Ltght duty
Medtum duty
BREITENBUSH
QUADRANGLE LOCATION
0(CLINAT10N AT C(Nl[R O r Sli[[!
ATT I TU DES
N
Locations of most contacts
are inferred from the dis­
tribution of rock types in
iso lated outcrops
Strikes and dips of bedded
tuffs and epic lastic rocks
in the Breitenbush Forma­
tion
HOT S P R I N G S , OREG.
N4445- W l 2 1 4 5 / 1 5
1961
FAULTS
G e o l ogi c C ross Sect ion
. . . . . . . . . .
Ea.posed
G ran i te
S.
R i ve r
A
5 , 000
Clac kamas
Pea k s
Inferred
P i nhead
BuI Ie
RA D I 0�1 ET R I C AGES
-
-------_/--�==:==-'l1=:::=:==::jT�o��==�==��====�
-...���7-=::::========:::=::::
...;
::
_'_T�o
\
/""
.- ----....
--...._
._,.
.-...
..
��
...___
_
r...._
.._
� -
>- I
'
-
3, 000 -
'
1 , ooo -
{
Te
-
_
_
_
I
_
_
_
_
_
_
_
_ _ _
?
-
----
?
--
4 . 7 4 my
Qb
------ ?
--- -
-
-
? - - - - -- - - -
( 3 . 60 my )
J- - - ·
K/Ar who le-rock age ob­
tained for this report
Prepare d i n c o n fo rma nce w i th ORS 5 1 6 . 0 30
F u nded i n p a r t under U . S . D e p a r tm e n t
o f E n e rgy C o n t ra c t D E - FC07 - 7 9 I D 1 2044
Concea led
K/Ar who le-rock or minera l
age taken from previous ly
pub lished reports
E x a c t l oc a t i ons o f s amp l e s u s ed f o r a g e da t i n g a re g i v e n i n a p p e n d i x o f t e x t
Geology b y Craig White, 1979.