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dss

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(age of Mazama ash)

Postglacial

7.7 ka

17-18 ka

20 ka

30 ka

50 ka

100 ka

200 ka

Early Holocene or

latest Pleistocene

Late or middle

Pleistocene

Middle Pleistocene Late Pleistocene

QUATERNARY

Holocene

CORRELATION OF MAP UNITS

SURFICIAL DEPOSITS VOLCANIC ROCKS

Broken Top and Vicinity

North Sister and Vicinity

Middle Sister and Vicinity

South Sister and Vicinity

[Vertical arrows indicate age uncertainties of a few units; extended boxes indicate known age ranges for long-lived units. Stipple indicates 

units that are partly or wholly pyroclastic. See Description of Map Units (in pamphlet) for specific unit age assignments]

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mdw

mec

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msb

msc

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msp

mtb

mth′

mth

mts

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anh

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mwy

myl

mys

myw

abt

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bwy

mbt

mbw

mws

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ruc

acc

acp

bbr

bcc

bes

bhs

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bnf

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bsl

bss

btk

bwl

rct

rdc′ rdc

rdh

rgl

rkb

rmc

rpc

rpg

rrm

rsc′ rsc

rse

rsf

rsw

adl

aef

ahl

alc

aoc

asw

awc

awm

awr

dbh

dhr

dig

dlc

dlp

dms

dsn

dss

dsw

mcl

mhd

mhl

mls

mmi

mmm

mms

mms′

mmt

mnf

mnh

mrg

20

LIST OF MAP UNITS

[Stipple indicates units that are partly or wholly pyroclastic. See Description of Map Units (in 

pamphlet) for complete unit descriptions]

SURFICIAL DEPOSITS

Glacial ice (late Holocene)

Pumice deposits (late Holocene)

Pumiceous debris-flow deposits (late Holocene)

Alluvium (Holocene)

Glacial deposits, undivided (Holocene and late Pleistocene)

Surficial deposits, undivided (Holocene and late Pleistocene)

Debris-avalanche deposit (Holocene or latest Pleistocene)

Landslide deposit (Holocene or latest Pleistocene)

VOLCANIC ROCKS

SILICIC FOCUS

South Sister and Vicinity

Andesite dome of Lewis Glacier headwall (late Pleistocene)

Andesite of Eugene Glacier (late Pleistocene)

Andesite tephra fall of Hodge Crest (late Pleistocene)

Andesite intrusive complex of Hodge Crest (late Pleistocene)

Andesite west of Lost Creek Glacier (late Pleistocene)

Andesite of Lewis Glacier headwall (late Pleistocene)

Andesite south of Lewis Glacier (late Pleistocene)

Andesite of Park Creek (late Pleistocene)

Andesite of Prouty Glacier headwall (late Pleistocene)

Andesite tephra fall near base of Prouty Glacier headwall (late Pleistocene)

Andesite south of Newberry flow (late Pleistocene)

Andesite of West Fork Park Creek (late Pleistocene)

Dacite breccia of Lewis Glacier headwall (late Pleistocene)

Dacite southwest of Clark Glacier (late Pleistocene)

Dacite of Chambers Lakes (late Pleistocene)

Dacite north of Carver Lake (late Pleistocene)

Dacite of Dew Lake (late Pleistocene)

Dacite ejecta of South Sister summit (late Pleistocene)

Dacite of Goose Creek (late Pleistocene)

Dacite of Green Lakes (late Pleistocene)

Dacite of Kokostick Butte (late Pleistocene)

Dacite of Lewis Glacier headwall (late Pleistocene)

Dacite southeast of Moraine Lake (late Pleistocene)

Dacite north of Moraine Lake (late Pleistocene)

Dacite coulee west of Moraine Lake (late Pleistocene)

Dacite north of Teardrop Pool (late Pleistocene)

Silicic dacite north of Teardrop Pool (late Pleistocene)

Dacite pumice fall of Prouty Glacier headwall (late Pleistocene)

Dacite of Red Meadow (late Pleistocene)

Dacite west of Lost Creek Glacier (late Pleistocene)

Dacite of Wickiup Plain (late Pleistocene)

Basaltic andesite of Teardrop Pool (late Pleistocene)

Rhyolite of South Sister climbers trail (late Pleistocene)

Rhyolite of “Devils chain” (late Holocene)

Rhyolite of Devils Hill (late Pleistocene)

Rhyolite of Green Lakes (late Pleistocene)

Rhyolite of Kaleetan Butte (late Pleistocene)

Rhyolite of Mesa Creek (late Pleistocene)

Rhyolite of Park Creek (late Pleistocene)

Rhyodacite of Prouty Glacier (late Pleistocene)

Rhyolite of Rock Mesa (late Holocene)

Rhyolite of Separation Creek (late Pleistocene)

Rhyolite southeast of Lewis Glacier (late Pleistocene)

Rhyolite of South Fork Whychus Creek (late Pleistocene)

Rhyolite southwest of Lewis Glacier (late Pleistocene)

Middle Sister and Vicinity

Andesite of Demaris Lake (late Pleistocene)

Andesite tephra fall at base of east face of Middle Sister (late Pleistocene)

Andesite of headwaters of Linton Creek (late Pleistocene)

Andesite of Linton Creek (late Pleistocene)

Andesite of Obsidian Creek (late Pleistocene)

Andesite of southwest slope of Middle Sister (late Pleistocene)

Andesite west of Collier Glacier (late Pleistocene)

Andesite west of Middle Sister (late Pleistocene)

Andesite west of Renfrew Glacier (late Pleistocene)

Dacite of “Black Hump” (late Pleistocene)

Dacite of Hayden Glacier–Renfrew Glacier col (late Pleistocene)

Dacite of Irving Glacier (latest Pleistocene)

Dacite of Linton Creek (late Pleistocene)

Dacite of Lane Plateau (late Pleistocene)

Dacite of Middle Sister summit (late Pleistocene)

Dacite north of Separation Creek (late Pleistocene)

Dacite of Sister Spring (late Pleistocene)

Dacite domes southwest of Middle Sister (late Pleistocene)

Basaltic andesite of Camp Lake (late Pleistocene)

Basaltic andesite of Hayden Glacier–Diller Glacier cleaver (late Pleistocene)

Basaltic andesite of headwaters of Linton Creek (late Pleistocene)

Basaltic andesite of Linton Spring (late or middle Pleistocene)

Basaltic andesite intrusion of Middle Sister (late Pleistocene)

Basaltic andesite of Montague Memorial (late Pleistocene)

Basaltic andesite of Middle Sister (late Pleistocene)

Pyroxene-bearing variant of the basaltic andesite of Middle Sister (late 

Pleistocene)

Basaltic andesite tuff of Middle Sister (late Pleistocene)

Basaltic andesite of North Fork Whychus Creek (late Pleistocene)

Basaltic andesite north of Hayden Glacier (late Pleistocene)

Basaltic andesite of Renfrew Glacier (late Pleistocene)

Basaltic andesite of Middle Sister summit (late Pleistocene)

Rhyolite of Obsidian Cliffs (late Pleistocene)

MAFIC PERIPHERY

North Sister and Vicinity

Andesite agglutinate north of Hayden Glacier (late Pleistocene)

Hornblende-bearing andesite southeast of Yapoah Crater (late Pleistocene)

Andesite west of upper Alder Creek (late Pleistocene)

Basalt of Alder Creek (late or middle Pleistocene)

Basalt of Brush Draw (late or middle Pleistocene)

Basaltic andesite east of Yapoah Lake (late Pleistocene)

Basaltic andesite of fissure vent south of Yapoah Lake (late Pleistocene)

Basaltic andesite of South Matthieu Lake (late Pleistocene)

Basaltic andesite of North Matthieu Lake (late Pleistocene)

Basaltic andesite of North Sister (late and middle Pleistocene)

Basaltic andesite north of Trout Creek (late Pleistocene)

Basaltic andesite north of Scott Pass (late Pleistocene)

Basaltic andesite south of Scott Pass (late Pleistocene)

Basaltic andesite south of Trout Creek (late or middle Pleistocene)

Basaltic andesite west of upper Alder Creek (late Pleistocene)

Basaltic andesite scoria cone west of Yapoah Lake (late Pleistocene)

Basaltic andesite of Yapoah Lake (late Pleistocene)

Basaltic andesite southwest of Yapoah Lake (late Pleistocene)

Basaltic andesite window west of Yapoah Lake (late or middle Pleistocene)

Broken Top and Vicinity

Andesite and dacite of Broken Top (middle Pleistocene)

Andesite of Whychus Creek (middle Pleistocene)

Basalt of Whychus Creek (middle Pleistocene)

Basaltic andesite of Broken Top (middle Pleistocene)

Basalt of Whychus Creek bridge (middle Pleistocene)

Basaltic andesite west of Snow Creek (middle Pleistocene)

Rhyodacite southwest of Golden Lake (late or middle Pleistocene)

Rhyodacite of Upper Chush Falls (middle Pleistocene)

Peripheral Centers and Other Lavas

Andesite of Collier Cone (Holocene)

Andesite of Pole Creek scoria cone (late or middle Pleistocene)

Basalt of Sparks Lake boat ramp (early Holocene or latest Pleistocene)

Basalt of Cayuse Crater (early Holocene or latest Pleistocene)

Basalt east of Sparks Lake (early Holocene or latest Pleistocene)

Basalt south of The Husband (middle Pleistocene)

Basalt of James Creek (middle Pleistocene)

Basalt of North Fork Whychus Creek (middle Pleistocene)

Basalt of Sphinx Butte (middle Pleistocene)

Basalt southeast of Sparks Lake (early Holocene or latest Pleistocene)

Basalt of Spruce Spring (late Pleistocene)

Basalt and basaltic andesite of Talapus and Katsuk Buttes (latest Pleistocene)

Basalt of lower Whychus Creek (late or middle Pleistocene)

Basalt west of Millican Crater (late Pleistocene)

Dacite of Mesa Creek (middle Pleistocene)

Dacite east of Sink Creek (late or middle Pleistocene)

Dacite of Todd Lake (middle Pleistocene)

Basaltic andesite of Black Crater (late or middle Pleistocene)

Basaltic andesite of Bare Lake (middle Pleistocene)

Basaltic andesite north and south of Demaris Lake (middle Pleistocene)

Basaltic andesite west of Dutchman Flat (late or middle Pleistocene)

Basaltic andesite and basalt of “Egan Cone” (early Holocene)

Basaltic andesite of The House Rock (late Pleistocene)

Basaltic andesite of Koosah Mountain (late Pleistocene)

Basaltic andesite of Little Brother (late Pleistocene)

Basaltic andesite of Le Conte Crater (early Holocene or latest Pleistocene)

Basaltic andesite of Millican Crater (late Pleistocene)

Basaltic andesite of Park Meadow (late or middle Pleistocene)

Basaltic andesite of Sims Butte (latest Pleistocene)

Basaltic andesite of Separation Creek (late Pleistocene)

Basaltic andesite of South Fork Whychus Creek (middle Pleistocene)

Basaltic andesite of Soap Creek–North Fork Whychus Creek confluence (late or 

middle Pleistocene)

Basaltic andesite and basalt of Trout Creek Butte (middle Pleistocene)

Basaltic andesite of The Husband (middle Pleistocene)

Basaltic andesite southeast of “Todd Creek” (middle Pleistocene)

Basaltic andesite of The Wife (middle Pleistocene)

Basaltic andesite of Whychus Creek (middle Pleistocene)

Basaltic andesite of Yapoah Crater (Holocene)

Rhyodacite southwest of Todd Lake (middle Pleistocene)

Rhyolite of Dome 5803 (late Pleistocene)

Shevlin Park Tuff (middle Pleistocene)

EXPLANATION OF MAP SYMBOLS

Contact—Long-dashed where approximately located; short-dashed where inferred; 

dotted where concealed. Internal contacts in volcanic units indicate individual 

emplacement lobes; in surficial units, deposits of different depositional intervals

Dikes

Moraine crests

Little Ice Age

Early Neoglacial

Younger Dryas

Last Glacial Maximum

Ejecta rim

Lava-levee crest

Lava-flow direction

Strike and dip of ejecta and stacks of thin lava flows

Volcanic craters and partial crater rims—Hachures point inward

Volcanic vent (other than craters and fissures)

Volcanic fissure vent 

SOUTH NORTH

South Sister

Newberry flow

Broken Top

lava flows

Middle Sister

“Black Hump”

Black Crater

North Sister

Green Lakes

Three Sisters volcanic chain forms 20-km-long reach along crest of the Cascade Range. Aerial view northward along east side of edifices. Photograph by Don Graham, helicopter pilot.

Any use of trade, product, or firm names in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, 

Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3186/

Suggested citation: Hildreth, Wes, Fierstein, Judy, and Calvert, Andrew T., 2012, Geologic 

map of Three Sisters volcanic cluster, Cascade Range, Oregon: U.S. Geological Survey 

Scientific Investigations Map 3186, pamphlet 107 p., 2 sheets, scale 1:24,000. (Available at 

http://pubs.usgs.gov/sim/3186/.) Printed on recycled paper

Geologic Map of Three Sisters Volcanic Cluster, Cascade Range, Oregon

By

By Wes Hildreth, Judy Fierstein, and Andrew T. Calvert

2012

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3186

Sheet 2 of 2

Pamphlet and CD-ROM accompany map