U.S. Department of the InteriorU.S. Geological Survey

Geologic Map of the North Cascade Range, WashingtonBy

Ralph A. Haugerud and Rowland W. Tabor2009

Prepared in cooperation withWashington State Division of Geology and Earth Resources, U.S. National Park Service, and U.S. Forest Service

NOTE: See Nontechnical Pamphlet for figures that are not on this map sheet

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.

Digital files available at http://pubs.usgs.gov/sim/2940

Scientific Investigations Map 2940Sheet 2 of 2

Pamphlets accompany map

Ruth Mountain

GunnPeak

MountBaring

GrottoMountain

EldoradoPeak

Three Fools Peak

HozomeenMountain

TwinSisters

DomePeak

Le Conte Glacier

Old GuardPeak

GlacierPeak Spine

PointMountBaker

Figure 8. View northwest from Bacon Peak [MBsw]. Rocks of Easton Terrane (Shuksan Greenschist) form Anderson Butte [MBsw]. A huge block of ultramafic rock (dunite) in Bell Pass Mélange underlies Twin Sisters [MBsw]. Mount Baker volcano dominates skyline.

Figure 13. Beds of sandstone (Eocene Swauk Formation) in older extensional deposits on south side of the east ridge of Summit Chief Mountain [SKse].

Figure 14. Disrupted sandstone, greenstone, and light-colored dikes in argillite matrix of western mélange belt unit TKwb, South Fork Stillaguamish River [SRsw].

Figure 15. View east from Mount Index [SKnw] across Skykomish River valley to Gunn and Baring peaks [SKne], underlain by large erosion-resistant tectonic slices of migmatitic gneiss in less-resistant sedimentary rocks of eastern mélange belt. Grotto Mountain is composed of granodiorite of Miocene Grotto batholith, the eroded root of a Cascade Magmatic Arc volcano. Mountans on skyline beyond are carved from rocks of Nason terrane (in Wenatchee block), predominantly Late Cretaceous Chiwaukum Schist and Mount Stuart batholith. Foreground rock is Jurassic metagabbro, another tectonic slice mixed into eastern mélange belt in latest Cretaceous or early Tertiary.

Figure 16. Large lumps of erosion-resistant rock dotting serpentinite matrix of Helena-Haystack mélange (units TKhm, TKhg). Most lumps are greenstone or Shuksan Greenschist. View northwest from ridge southwest of Day Lake [SRnw].

Figure 17. View of Eldorado Peak [MBse], looking northeast from divide between Sibley and Marble Creeks. In foreground, metaconglomerate of late Cretaceous Cascade River Schist contains cobbles (deposited in Triassic) stretched to form streaks. Orthogneiss of Eldorado pluton visible in background. Small glaciers and moraine deposits in valley are visible behind geologist.

Figure 19. View from Mount Winthrop [RMnw] south along Cascade Crest. Well-bedded sandstone of Cretaceous Three Fools Sequence (rocks of Methow Ocean) form crest. Divide at right was rounded by overriding Cordilleran Ice Sheet. Mixed glacial deposits (drift) from ice sheet and local alpine glaciers are visible in valley bottom.

Figure 20. Hozomeen greenstone in Methow block north of Little Beaver Creek [MBne], where it is probably Triassic, and on Hozomeen Mountain [MBne], where it is Late Paleozoic. View northeast from ridge south of Little Beaver Creek.

Figure 12. Granite of Cascade Pass family on the west wall of Nooksack cirque in foreground. Ruth Mountain [MBnw] to northeast is carved from volcanic breccia of Pliocene Hannegan Caldera. Both rocks formed in the Cascade Magmatic Arc. Extensive glacial moraine covers valley floor.

Figure 7. Looking south from east ridge of Mount Formidable [SRne]. Uplift and erosion, especially glacial erosion, exposed rocks that formed deep in the Earth's crust. Rocks of the Chelan Mountains terrane, including Cascade River Schist, form foreground cliffs. Underlying metamorphosed Marblemount pluton in Old Guard Peak [SRne] extends along jagged ridge into middle foreground. The Cloudy Pass batholith, a Miocene Cascade Arc pluton, supports Dome Peak [SRne] and Spire Point [SRne] in middle background. Glacier Peak volcano in the Cascade Magmatic Arc erupted on top of these eroded older rocks.

Figure 1. Map of northwestern Washington showing area of geologic map. Eight 1:100,000 topographic quadrangles that form geologic map are outlined and labeled. Quadrangle abbreviations and compass quadrants are used in the text as location codes to find places on the map, for example [MBse] is the southeastern part of the Mount Baker quadrangle. Abbreviations for all quadrangles are shown here and along the edge of the geologic map.

White

YakimaC

olum

bia

River

Skykomish

Stillaguamish

River

Methow

RiverChelan

LakeSk

agit

SaukRiver

River

River

River

Riv

er

PUGET SOU

ND

CHELAN [C]

TWISP [T]SAUK RIVER [SR]

ROBINSON MOUNTAIN[RM]

MOUNT BAKER [MB]

SKYKOMISH RIVER [SK]

SNOQUALMIE PASS [SP] WENATCHEE [W]

0 20 40 MILES

0 40 80 KILOMETERS

MountMisch

GlacierPeak

UNITEDSTATES

MountBaker

VedderMountatn

SEATTLE

OLYMPICMOUNTAINS

San JuanIslands

Skykomish

BRITISH COLUMBIA

SedroWolley

BELLINGHAM

Winthrop

Twisp

Stehekin

RobinsonMountain

MountStuart

MountRainier

Wenatchee

Leavenworth

SnoqualmiePass

WashingtonPass

Enumclaw

Chelan

BonanzaPeak

JackMtn

Monroe

CANADA

AREA OF MAP

Concrete

123°

49°

48°

47°

122° 121° 120°

Darrington

WASHINGTON

Figure 1

Figure 2. Map showing sources of geologic data for the Twisp 1:100,000 topographic quadrangle and adjacent area. Line pattern indicates surficial geology modified from original sources using aerial photographs. 1. Barksdale, 1975; 2. Cater and Crowder, 1967; 3. Cater and Wright, 1967; 4. Dragovich and Norman, 1995; 5. Dragovich and others, 1997; 6. Haugerud, R.A., Mahoney, J.B., and Tabor, R.W., unpub. U.S. Geological Survey field maps (1990-2003); 7. Hopson and Mattinson, 1994 and C.A. Hopson, written commun., 2005; 8. Libby, 1964; 9. Miller, 1987; and 10. Tabor, 1961.

1

2 3

4

5

6

8

9

10

7

48°

48°30’121° 120°

Figure 3. Sketch showing plate tectonic processes. The surface of the Earth is covered by many interlocking plates (lithosphere or crust). New crust forms at the mid-ocean ridge where oceanic plates move apart, allowing molten rock (magma) to reach the surface and erupt as basalt lavas. An oceanic plate descends below a continental plate at a subduction zone where plates converge; rocks of both plates melt at depth to produce magma that rises toward the surface. Much of the magma collects in large masses (magma chambers) in the continental crust. Some magma reaches the surface to build a line of volcanoes (volcanic arc). Eventually the magma in the chambers cools and crystallizes to become plutonic intrusive igneous rock. Sedimentary rocks on the ocean floor and some of the oceanic crust scrapes off at depth to become metamorphic rocks. Blow-up shows idealized layering of oceanic lithosphere (ophiolite).

VOLCANICARC

plastic mantle

rigid mantle

plastic mantle

sedimentaryrocks

oldersedimentary

rocks

MID-OCEANRIDGE

basalt lavaserupt to formoceanic plate

melting zone(source of igneous rocks)

SUBDUCTED OCEAN PLATE (OCEANIC LITHOSPHERE)

rigid mantle CO

NT

INE

NTA

LC

RU

ST

CO

NT

INE

NTA

LLI

TH

OS

PH

ER

E

metamorphicrocks forming

OCEANICLITHOSPHERE

melting zone(more igneous rocks)

Ophiolite layering

sedimentspillow basalt

dikes

gabbroultramafic rock

OCEANICCRUST

MANTLE

ocean floor basalt

SUBDUCTION

ZON

E

Figure 4. Map showing major geologic structures and major metamorphic episodes in the North Cascades, Washington. Areas of multiple regional metamorphism are sketched from field and laboratory data and descriptions in the literature. Boundaries are approximate. Domains shown are described in Tabor and Haugerud (1999).

early Tertiary and Late Cretaceous metamorphism

early Late Cretaceous metamorphism

early Late Cretaceous and Early Creataceous

metamorphism

Early Cretaceous blueschist metamorphism

of Easton terrane

Early Cretaceous and local Jurassic

metamorphism

Contact—Dotted where uncertain

Fault—Dashed where uncertain; dotted where projected under cover

or intruded by younger rocks

WE

STE

RN

D

OM

AIN

METHOW

METAMORPHIC

CORE

DOMAIN

DOMAIN

122°49°

121° 120°

47°

Straig

ht

Ross Lake Fault Zone (System)

Fault

Entiat

PasaytenFault

Creek

Fault

Leavenworth

Fault

Darrington-Devils Mtn Fault Zone (D

DM

FZ)

DDMFZ

(projected)

Chilwaukum

Graben

MELA

NG

E BELTS

NORTHWEST

CASCADE

SYSTEM

WEN

ATCH

EE BLO

CK

CHELAN BLO

CK

METHO

W BLO

CK

OKAN

OG

AN

BLOCK

Ingalls Complex

Columbia Rver Basalt Group

Extensional Basins

VinegarFault

Qa

Qu

Qt

QTl

Qlh

Qvr

Qvt

Qva

Qud

Qgf

Qcav

QTcc

QTcp

Tcaf

Tcas

Tcao

Tcai

Tes

Tees

Teev

Tev

TKwb

TKwg

TKeb

TKebg

KJb

KJya

KJts

KJv

TKsg

TKso

TKsn

TKto

TKgo

Kt

Kg

TKns, Kns

TKnu, Knu

TKcs, Kcs

TKmd, Kmd

TKmm

KJi

Jnb

Jnbm

Jl

Ktd

Kog

Kor

Kot

KJh

KJog

h

TKsx

TKm, Km

TKmo

Kpv

Kps

Ktf

KJos

Kpc

Ktm

Kswg

Kcxm

TKrb

Jis

Jbi

Jbs

Knmg

Kncs

Jc

PDc

Ked

Kes

Ket

TKhm

TKhg

KJn

Jnw

Tei

Trr

Tyw

Tyg

Te

Qpf

QTog

Qag

Qga

LIST OF MAP UNITS[See technical or nontechnical pamphlets for unit descriptions. Note colors on the map vary as the underlying shaded-relief base varies. Unit age in parentheses after the unit name is the age of assemblage or metamorphism for mélange and metamorphic units. Location codes, such as "[MBnw]," following a place name, unit name, or geologic feature name indicates a location in the northwest quadrant of the Mount Baker quadrangle. The eight 1:100,000-scale quadrangles are outlined on the map, and quadrangle names and their abbreviations are labeled along the edges of the map, as well as on figures 1 and 5. The location code may consist of a quadrangle abbreviation or a combination of quadrangle and quadrant abbreviations. A location code at the end of the rock descripton gives the unit location on the map]

UNCONSOLIDATED DEPOSITS

NONGLACIAL DEPOSITSAlluvium of valley bottoms (Holocene and Pleistocene)

Alluvium (Holocene and Pleistocene)

Talus deposits (Holocene and Pleistocene)

Landslide deposits (Holocene, Pleistocene, and Pliocene?)

Lahars (Holocene and Pleistocene)

GLACIAL DEPOSITSAlpine glacial deposits (Holocene and Pleistocene)

Deposits of alpine glaciers and Cordilleran Ice Sheet (Holocene and Pleistocene)

Deposits of Vashon stade of Fraser glaciation of Armstrong and others (1965) (Pleistocene)Recessional outwash deposits

Till

Advance outwash deposits

Upland deposits (Holocene and Pleistocene)

Deposits of glacial outburst floods (Pleistocene)

GLACIAL AND NONGLACIAL DEPOSITSNonglacial and glacial sedimentary deposits older than Fraser glaciation (Pleistocene)

Older gravel (Pleistocene, Pliocene, and Miocene?)

ROCKS OF CASCADE MAGMATIC ARCRocks of young Cascade volcanoes (Holocene and Pleistocene)

Caldera deposits (Pleistocene, Pliocene, and Miocene)

Intrusive rocks of Cascade Pass family (Pleistocene, Pliocene, and Miocene)

Volcanic rocks of Fifes Peak episode (Miocene)

Intrusive rocks of Snoqualmie family (Miocene and Oligocene)

Volcanic and sedimentary rocks of Ohanapecosh episode (Oligocene)

Intrusive rocks of Index family (Oligocene)

FLOOD BASALT AND ASSOCIATED DEPOSITSEllensburg Formation (Miocene)

Yakima Basalt Subgroup of Columbia River Basalt Group (Miocene)Wanapum Basalt

Grand Ronde Basalt

ROCKS OF LATE- AND POST-OROGENIC TRANSTENSION

EXTENSIONAL DEPOSITSExtensional sedimentary rocks (early Oligocene and Eocene)

Early extensional sedimentary rocks (middle and early Eocene)

Silver Pass Volcanic Member of Swauk Formation

Volcanic rocks (early Oligocene and Eocene)

OTHER ROCKSIntrusive rocks (middle Eocene)

Raging River Formation (middle and early? Eocene)

OROGENIC AND PRE-OROGENIC ROCKS MOSTLY WEST OF STRAIGHT CREEK FAULT

ROCKS SOUTHWEST OF DARRINGTON-DEVILS MOUNTAIN FAULT ZONERocks of western mélange belt (middle Eocene to Late Cretaceous)

Quartz Mountain stock (Middle Jurassic)

Rocks of eastern mélange belt (middle Eocene to Late Cretaceous)

Migmatitic gneiss

ROCKS IN DARRINGTON-DEVILS MOUNTAIN FAULT ZONEHelena-Haystack mélange (middle Eocene and (or) Late Cretaceous)

Serpentinite

Blocks of resistant rock

ROCKS NORTHEAST OF DARRINGTON-DEVILS MOUNTAIN FAULT ZONE

Northwest Cascade System

Rocks of AutochthonNooksack Formation (Early Cretaceous to Middle Jurassic)

Wells Creek Volcanic Member

Welker Peak and Excelsior NappesBell Pass mélange (Cretaceous to Late Jurassic)

Yellow Aster Complex of Misch (1966) (Paleozoic or older protolith age)

Twin Sisters Dunite of Ragan (1961, 1963)

Vedder Complex of Armstrong and others (1983) (pre-Permian protolith age)

Chilliwack River terraneCultus Formation of Brown and others (1987) (Early Jurassic and Late Triassic)

Chilliwack Group of Cairnes (1944) (Permian, Carboniferous, and Devonian)

Shuksan Nappe

Easton terrane

Tonalite gneiss of Hicks Butte (Early Cretaceous)

Easton Metamorphic SuiteDarrington Phyllite (Early Cretaceous)

Shuksan Greenschist (Early Cretaceous)

OROGENIC AND PRE-OROGENIC ROCKS EAST OF STRAIGHT CREEK FAULT

ROCKS UNIQUE TO WENATCHEE BLOCK

Ingalls terrane

Ingalls terrane (Jurassic)

Resistant blocks of igneous and meta-igneous rocks

Resistant blocks of sedimentary rocks

Nason Terrane

Nason Ridge Migmatitic Gneiss (Late Cretaceous)

Chiwaukum Schist (Late Cretaceous)

ROCKS IN WENATCHEE AND CHELAN BLOCKS

Terrane overlap units and stitching plutonsSkagit Gneiss Complex (middle Eocene to Late Cretaceous)

Orthogneiss

Orthogneiss of The Needle

Tonalitic orthogneiss (middle Eocene to Late Cretaceous)

Granodioritic orthogneiss (middle Eocene to Late Cretaceous)

Tonalitic plutons (Late Cretaceous)

Granodioritic plutons (Late Cretaceous)

Chelan Mountains terraneNapeequa Schist (middle Eocene to Late Cretaceous)

Ultramafic rock

Cascade River Schist (middle Eocene to Late Cretaceous)

Marblemount plutons (middle Eocene to Late Cretaceous)

Magic Mountain Gneiss (middle Eocene to Late Cretaceous)

Swakane terraneSwakane Biotite Gneiss (Late Cretaceous)

Terrane uncertainChelan Migmatite Complex of Hopson and Mattinson (1994) (Cretaceous)

ROCKS UNIQUE TO ROSS LAKE FAULT ZONERuby Creek heterogeneous plutonic belt of Misch (1966) (middle Eocene to Late Cretaceous)

Skymo Complex of Wallace (1976) (middle Eocene to Late Cretaceous)

Metamorphosed rocks of Methow Ocean (middle Eocene to Late Cretaceous)

Tonalitic orthogneiss (middle Eocene to Late Cretaceous)

ROCKS IN METHOW BLOCKPipestone Canyon Formation (Late Cretaceous)

Onlap assemblage and stitching plutonsTonalite plutons in Methow block (Late Cretaceous)

Pasayten Group of Kiessling and Mahoney (1997) (Late Cretaceous)Volcanic rocks

Sedimentary rocks

Rocks of Methow Ocean and onlap assemblagesThree Fools sequence of Haugerud and others (2002) (Cretaceous)

Older sedimentary rocks (Early Cretaceous and Late Jurassic)

Rocks of Methow Ocean floorTonalite intrusions (Early Cretaceous and Late Jurassic)

Newby Group of Mahoney and others (2002) (Late Jurassic)

Metamorphic rocks of McClure Mountain

Ladner Group of Mahoney (1993) (Middle Jurassic)

Hozomeen terraneHozomeen Group (Mesozoic and Paleozoic)

ROCKS IN OKANOGAN BLOCK

Okanogan terraneTonalite and diorite (Late Cretaceous)

Granite and granodiorite (Early Cretaceous)

Remmel batholith (Early Cretaceous)

Older tonalite (Early Cretaceous)

Hornblendic metamorphic rocks (Early Cretaceous and Jurassic)

Mylonitic granodiorite, gneissic trondhjemite, and banded gneiss (Early Cretaceous and Jurassic)

EXPLANATION OF MAP SYMBOLS

GEOLOGIC SYMBOLS

Contact—No contact where approximately located or gradational (mostly unit Qud)

Fault—Dotted where concealed

High-angle fault

Thrust fault

Low-angle fault—Extensional fault

GEOGRAPHIC SYMBOLS

Town

Major highway

Road

Trail

River

Water boundary—Blue boundary shown at edge of lake, or large river

Glacier or snow

Mountain or peak

Park, wilderness, recreation area, or scenic highway boundary

Topographic map (1:100,000 scale) boundary—Name [abbreviation] of topographic map labeled along east and west edges of map

Tes

TKhg

TKhm

TKwb

TKwg

TKeb

Jbs

JisJbi

Jbs

JisJbi

Teev

TKwb

TKeb

Miocene

Oligocene

TERTIARY

EarlyOligocene(?)

MiddleEocene

Late Eocene

EarlyEocene

Oligocene(?)

Eocene

Early

Cre

tace

ous

ROCKS SOUTHWEST OFDARRINGTON-DEVILS

MOUNTAIN FAULT ZONE

ROCKS INDARRINGTON-DEVILS

MOUNTAIN FAULT ZONE

52

47

40

37

36

28

25

19

21

20

12

6

Unconformity

Unconformity

Te

Tyw

Trr

Qa

QTl

Qlh

Fra

ser

glac

iati

on Holocene

PleistoceneQUATERNARY

Pliocene5

2.41.60.7

0.55

0.01

CORRELATION OF MAP UNITS[For mélange and metamorphic units, position of boxes with solid boundaries indicates age of assemblage

or metamorphism, respectively; position of boxes with dashed boundaries indicates age of protolith.]

NONGLACIAL DEPOSITS GLACIAL DEPOSITS

QagQvr Qvt Qva

Qpf

QTog

Qud Qcav

QTcc

Qt

GLACIAL ANDNONGLACIAL DEPOSITS

Tcai

Tcao

Tcaf

QTcp

Tcas

Tyg

ROCKS OFCASCADE MAGMATIC ARC

Tev

Tei

ROCKS OF LATE- AND POST-OROGENIC TRANSTENSION

Eoce

ne a

nd(o

r) C

reta

ceou

s

Welker Peak and Excelsior Nappes Shuksan NappeRocks of theAutochthon

KJya

KJts

KJn

KJb

Jnw

J^c

PDc

Ked Kes

Early

Cre

tace

ous

Mid

dle

Jura

ssic

Perm

ian,

Car

bon-

ifero

us, a

nd D

evon

ian

Early

Jura

ssic

and

Late

Tria

ssic

Permian

KJv

KJv

KJya

KJb

ROCKS IN WENATCHEE AND CHELAN BLOCKS

Kswg

Kswg

Kncs

Kncs

Knmg

Nason terrane

Swakaneterrane

TKmmKmdKcs

ROCKS UNIQUE TO ROSSLAKE FAULT ZONE

TKsx

TKm

MzPzh

mid

dle

Eoce

ne to

Lat

e C

reta

ceou

s

TKrb

Kps Kpv

Ktf

KJos

KJiJnb

JlEa

rlyC

reta

ceou

s

Early

Cre

tace

ous

and

Lat

e Ju

rass

ic

Mid

dle

Jura

ssic

Late

Cre

tace

ous

Kog

Kor Kot

Early

Cre

tace

ous

and

Jur

assi

c

CRETACEOUS

JURASSIC

TRIASSIC

PERMIAN ANDPENNSYLVANIAN

TERTIARY ANDCRETACEOUS

CENOZOICANDMESOZOIC

MESOZOIC

PALEOZOIC

PALEOZOICAND OLDER

Easton terrane

Ingalls terrane

ChilliwackRiver terrane

TKmo

Qu

Ktm

Jnbm

Ktd

Kpc

OROGENIC AND PRE-OROGENIC ROCKS EAST OF STRAIGHT CREEK FAULT

EXTENSIONALDEPOSITS

TKebg

Kcxm

Kcxm

KJogKJh

Qgf

Km

Tees

TKwg

Ket

Ked KesKet

Qga

TKhg

TKhm

Kns

?

?

TKm

TKsg TKso TKsn TKto TKgo

Terrane overlap units and stitching plutons

Kt Kg

Knu

TKmd

Kmd

TKcsTKns

TKnu

Chelan Mountains terrane

TKmm

Kcs

Kns

Terraneuncertain

OROGENIC AND PRE-OROGENIC ROCKS MOSTLY WEST OF STRAIGHT CREEK FAULT

Approximate age1

(millions of years)

156

220

90

73

UNCONSOLIDATED DEPOSITS

OTHER ROCKS

Hozomeenterrane

PasaytenGroup

Three Foolssequence

Oldersedimentary

rocks

Roc

ks o

f Met

how

Oce

an a

ndon

lap

asse

mbl

ages

FLOOD BASALT ANDASSOCIATED DEPOSITS

Vas

hon

stad

e

1 From time scale of Cowie and Bassett, 1989; Berggren and others, 1985.2 See Description of Map Units for specific unit age assignment.

ROCKS NORTHEAST OF DARRINGTON-DEVILS MOUNTAIN FAULT ZONE

Northwest Cascades System

ROCKS UNIQUE TOWENATCHEE BLOCK

Jura

ssic

,Tria

ssic

,an

d Pe

rmia

n

Early

Cre

tace

ous

and

Jura

ssic

Late

Pal

eozo

ic to

Mid

dle

Jura

ssic

C

reta

ceou

s to

Late

Jura

ssic

Skagit Gneiss Complex

ROCKS IN METHOW BLOCK

Onl

ap a

ssem

blag

ean

d st

itchi

ng p

luto

ns

Roc

ks o

f Met

how

Oce

an fl

oor

Okanogan terrane

ROCKS IN OKANOGAN BLOCK

MiddleJurassic

?

?

Geologic Age2

Geologic Age

Figure 5. Generalized geologic map of North Cascades, Washington. Towns: C, Concrete; CE, Cle Elum; Ch, Chelan; E, Enumclaw; El, Ellensburg; GF, Granite Falls; G, Glacier; H, Holden; L, Leavenworth; M, Methow; Ma, Mazama; NB, North Bend; S, Skykomish; T, Twisp; W, Wenatchee; Wa, Waterville; Wi, Winthrop. Geologic features: BMB, Bald Mountain batholith; BP, Black Peak batholith; CMB, Cooper Mountain batholith; DHP, Duncan Hill pluton; GC, Gamma Ridge caldera; GHB, Golden Horn batholith; HC, Hannegan caldera; KC, Kulshan caldera; MPS, Monument Peak stock; RRP, Railroad Creek pluton.

0 10 20 KILOMETERS 0 5 10 MILES

WINDYPASS THRUST

VINEGARFAULT

HOZOMEENTHRUST

WELKER PK THRUST

EXCELSIOR RIDGETHRUST

SH

UK

SA

N

PAYS

AYTEN

FAU

LT

FAU

LT

FAULT

LEV

EN

WO

RT

H

ENTIAT

THRU

ST

ST

RA

IGH

T

ROSS

LAKE

FAULT

ZON

E

CR

EE

KFA

ULT

DEVILS

-

MO

UN

TAIN

FAU

LTZO

NE

DARRINGTON

HC

KC

GHB

BP

RRP

H

Ch

M

T

Wi

Ma

GF

S

NB

E

El

W

L

Wa

CE

C

G

GC

CMB

DHP

X

BMB

MPS

MOUNTBAKER

GLACIERPEAK

MOUNTSTUART

47°

47°30’

48°

48°30’

49°122° 121° 120°

Snoq

ualm

ie P

ass

(SP)

Skyk

omis

h R

iver

(SK

)Sa

uk R

iver

(SR

)M

ount

Bak

er (

MB

)

Wen

atch

ee (

W)

Che

lan

(C)

Twis

p (T

)R

obin

son

Mou

ntai

n (R

M)

Eoc

ene

TE

RT

IAR

Y A

ND

QU

AT

ER

NA

RY

Olig

ocen

e, M

ioce

ne,

and

Plio

cene

Jurassic, Triassic,Permian, andPennsylvanian

ME

SOZ

OIC

AN

D T

ER

TIA

RY

FIGURE CORRELATION

Lat

e Ju

rass

ic-

Ear

ly .C

reta

ceou

s

Tri

assi

c an

dol

der(

?)

Early Cretaceous*

Penn

sylv

ania

n th

roug

h E

arly

Cre

tace

ous

Mid

dle

Jura

ssic

Unconsolidated deposits(Includes Quaternary

volcanoes and Miocene and (or) Pliocene gravel and breccia

at X and locally elsewhere)

Volcanic rocks of the CascadeMagmatic Arc

Plutonic rocksof theCascadeMagmatic Arc

Rocks in Wenatcheeand Chelan blocks

Rocks inMethow block

Rocks of Okanogan block

Helena-Haystackmelange Melange

belts

Rocks southwest ofand in DDMFZ

Skagit GneissComplex

ChelanMountains

terrane

Swakaneterrane Onlap assemblage, younger

marine sedimentary rocks, and metamorphic equivalents

Older marinesedimentary rocks

Newby unit

Hozomeen Group

Plutons: t, gneissic, tonalite and granodiorite; g, granite

Gneiss, schist, and migmatite

Lat

eC

reta

ceou

s*

Lat

r C

reta

ceou

s an

d ea

rly

Eoc

ene

Jurassic*

Cretaceous

Ear

lyC

reta

ceou

s

LateJurassic

UNCONFORMITY

Roc

ks o

f th

e M

etho

w O

cean

and

onla

p as

sem

blag

e

ROCKS OF LATE- AND POST-OROGENIC TRANSTENSION

Ladner Group

EarlyJurassic

Rocks of the Methow Ocean floor

Plio

cene

,Pl

eist

ocen

e a

nd H

oloc

ene

Volcanic andsedimentary rocks ofthe extensional event

Plutons of theextensional event

Orthogneissstitchingplutons Rocks of the North-

west Cascade System

Nasonterrane

Stitchingplutons

Stitching plutons

ChelanMigmatite Complex

Rocks northeastof DDMFZ

Jura

ssic

and

Ear

ly C

reta

ceou

s

PAL

EO

ZO

IC A

ND

ME

SOZ

OIC

Dev

onia

n, C

arbo

nife

rous

,Pe

rmia

n, a

nd T

rias

sic

Ingallsterrane

Melangebelts

Flood basalt

Pipestone CanyonFormation

ChelanMountains

terrane

Ingallsterrane

NooksackFormation

Welker Peak Nappe

ExcelsiorNappe

Welker PkNappe

ShuksanNappe

ShuksanNappe

t g

FIGURE SYMBOLS

Contact—Dotted where concealed

High-angle fault—Dotted where concealed

Thrust fault—Dotted where concealed

Low-angle normal fault—Dotted where concealed

Antiformal fold axis and plunge—Dotted where concealed

Synformal fold axis and plunge—Dotted where concealed

Overturned antiformal fold axis and plunge

[Metamorphic and structural units shown with metamorphic or assemblage age; uncolored boxes with dashed boundaries show protolith age. Asterisk indicates that box position represents protolith and metamorphic age (see technical discussion)]

X

2000

1600 2000

1200

800

1600

1200

PUGETLOBE

OKANOGAN LOBELA

KE

CHELAN

GLA

CIE

R

Mt Baker

RattlesnakeMtn

WENATCHEE

CONCRETE

GlacierPeak

MONROE

LEAVENWORTH

STEHEKIN

Jack Mtn

Mount Spickard

Gardner Mtn

PtarmiganPk

TWISP

MtPilchuck

DARRINGTON

122° 121°49°

47°30’

47°

48°

48°30’

120°

Figure 9. Digital relief map showing maximum extent of Cordilleran Ice Sheet (white with blue contours; interval 200 m) in the North Cascades during the Vashon stade; probable alpine glaciers on high peaks and beyond the margins of the main ice sheet are not shown (Waitt, 1972; Booth, 1990; Jon Riedel, written commun., 2005). Mount Baker, Rattlesnake Mountain [SPnw], Jack Mountain [RMnw], and many lesser peaks extended above the ice-sheet surface as nunataks.