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USGS Scientific Investigations Map 2940, Sheet 2

Scientific Investigations Map 2940 U.S. Department of the Interior Prepared in cooperation with State Division of and Earth Resources, U.S. National Park Service, and U.S. Forest Service Sheet 2 of 2 U.S. Geological Survey Pamphlets accompany map

123° 122° 121° 120° 121° 120° basalt VOLCANIC 122° 121° 120° 49° 48°30’ erupt to form ARC 122° 121° 120° oceanic plate MID-OCEAN 49° NORTHWEST OKANOGAN Zone (System) Ptarmigan River RIDGE Old Guard Mount Vedder Straight Peak Spine WESTERN Peak Peak Pk 49° Mountatn CANADA 5 BLOCK Point Baker Jack Mtn ocean floor basalt sedimentary Mt Baker ROBINSON UNITED METHOW Pasayten [MB] rocks early Tertiary and Late Le Conte Glacier Twin 2000 [RM] STATES 10 Cretaceous Sisters Jack METHOW BLOCK Mount 1600 San Juan BELLINGHAM Baker Mtn Robinson Mountain 4 CONCRETE 2000 Islands OCEANIC OCEANIC SU CHELAN BLOCK

Methow CRUST rigid mantle B CRUST CASCADE 48°30’ Gardner Mtn

LITHOSPHERE Creek DU Skagit C Fault Sedro 9 T rigid mantle DOMAIN Concrete CONTINENTAL TWISP plastic mantle plastic mantle IO Wolley Winthrop N early Late Cretaceous 6 melting zone CONTINENTAL Sauk older STEHEKIN Washington (source of igneous rocks) Z melting zone metamorphism sedimentary O (more igneous rocks) Entiat DARRINGTON 1600 Pass Twisp MANTLE N OKANOGAN Mount rocks E 1200 sediments P Misch SYSTEM LAKE LOBE U metamorphic G River Stehekin pillow basalt Glacier E D T Lake rocks forming a Peak River rr Stillaguamish Darrington River dikes i METAMORPHIC n g Vinegar Mt CHELAN S Glacier Chelan to Fault Fault O Bonanza n early Late Cretaceous 1200 U Peak gabbro Fault Pilchuck Peak -D 48° GLACIER N ultramafic rock e and Early Creataceous D SAUK RIVER [SR] TWISP [T] 2 3 v WENATCHEE BLOCK 48° i metamorphism ls Ophiolite layering SUBDUCTED OCEAN PLATE M Monroe 8 DOMAIN (OCEANIC LITHOSPHERE) t CORE MONROE Skykomish n OLYMPIC River F Chelan Figure 3. Sketch showing plate tectonic processes. The surface of the Earth is covered by many interlocking plates (lithosphere or crust). a 1 u l PUGET New crust forms at the mid-ocean ridge where oceanic plates move apart, allowing molten rock () to reach the surface and erupt as t

Z Figure 7. Looking south from east ridge of Mount Formidable [SRne]. Uplift and Skykomish Figure 8. View northwest from Bacon Peak [MBsw]. Rocks of Easton (Shuksan LOBE basalt lavas. An oceanic plate descends below a continental plate at a zone where plates converge; rocks of both plates melt at o DOMAIN Early Cretaceous LEAVENWORTH n Leavenworth River 48° MELANGE BELTS , especially glacial erosion, exposed rocks that formed deep in the Earth's crust. Greenschist) form Anderson Butte [MBsw]. A huge block of ultramafic rock (dunite) in e blueschist metamorphism depth to produce magma that rises toward the surface. Much of the magma collects in large masses (magma chambers) in the continental 800 ( Rocks of the Chelan Mountains terrane, including Cascade River Schist, form foreground [SK] CHELAN [C] D of Easton terrane Bell Pass Mélange underlies Twin Sisters [MBsw]. Mount Baker dominates crust. Some magma reaches the surface to build a line of volcanoes (). Eventually the magma in the chambers cools and D cliffs. Underlying metamorphosed Marblemount pluton in Old Guard Peak [SRne] skyline. 47°30’ Snoqualmie Mount M Pass 7 crystallizes to become plutonic intrusive igneous rock. Sedimentary rocks on the ocean floor and some of the oceanic crust scrapes off at Leavenworth Stuart F extends along jagged ridge into middle foreground. The Cloudy Pass batholith, a Miocene Rattlesnake WENATCHEE Z Wenatchee depth to become metamorphic rocks. Blow-up shows idealized layering of oceanic lithosphere (ophiolite). ) Mtn White Chilwaukum Cascade Arc pluton, supports [SRne] and [SRne] in middle Yakima Enumclaw background. volcano in the Cascade Magmatic Arc erupted on top of these River Figure 2. Map showing sources of geologic data for the Twisp 1:100,000 topographic Early Cretaceous and eroded older rocks. quadrangle and adjacent area. Line pattern indicates surficial geology modified from local [SP] WENATCHEE [W] metamorphism 47° original sources using aerial photographs. 1. Barksdale, 1975; 2. Cater and Crowder, Fault Mount AREA OF MAP 1967; 3. Cater and Wright, 1967; 4. Dragovich and Norman, 1995; 5. Dragovich and (projected) River Ingalls Complex 47° Rainier 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. Extensional Basins Contact—Dotted where Figure 9. Digital relief map showing maximum extent of Cordilleran 0 20 40 MILES uncertain Figure 1 Hopson, written commun., 2005; 8. Libby, 1964; 9. Miller, 1987; and 10. Tabor, 1961. Figure 4. Map showing major geologic structures and major (white with blue contours; interval 200 m) in the North 0 40 80 KILOMETERS Columbia WASHINGTON metamorphic episodes in the , Washington. NOTE: See Nontechnical Pamphlet for figures that are not on this map sheet Cascades during the Vashon stade; probable alpine on high peaks and beyond the margins of the main ice sheet are not shown Areas of multiple regional metamorphism are sketched from Fault—Dashed where field and laboratory data and descriptions in the literature. DDMFZ uncertain; dotted where (Waitt, 1972; Booth, 1990; Jon Riedel, written commun., 2005). Mount Figure 1. Map of northwestern Washington showing area of geologic map. Eight 1:100,000 topographic Boundaries are approximate. Domains shown are described Columbia Rver Basalt Group projected under cover Baker, Rattlesnake Mountain [SPnw], [RMnw], and quadrangles that form geologic map are outlined and labeled. Quadrangle abbreviations and compass in Tabor and Haugerud (1999). or intruded by younger rocks many lesser peaks extended above the ice-sheet surface as nunataks. quadrants are used in the text as location codes to find places on the map, for example [MBse] is the 47° southeastern part of the Mount Baker quadrangle. Abbreviations for all quadrangles are shown here and along the edge of the geologic map.


[See technical or nontechnical pamphlets for unit descriptions. Note colors on the map vary as the underlying shaded- ROCKS UNIQUE TO WENATCHEE BLOCK relief base varies. Unit age in parentheses after the unit name is the age of assemblage or metamorphism for mélange and Ingalls terrane 122° 120° metamorphic units. Location codes, such as "[MBnw]," following a place name, unit name, or geologic feature name 121° Jis Ingalls terrane (Jurassic) 49° EXCELSIOR RIDGE FIGURE SYMBOLS FIGURE CORRELATION indicates a location in the northwest quadrant of the Mount Baker quadrangle. The eight 1:100,000-scale quadrangles are THRUST [Metamorphic and structural units shown with metamorphic or assemblage age; uncolored boxes outlined on the map, and quadrangle names and their abbreviations are labeled along the edges of the map, as well as on with dashed boundaries show protolith age. Asterisk indicates that box position represents protolith Jbi HC figures 1 and 5. The location code may consist of a quadrangle abbreviation or a combination of quadrangle and quadrant Resistant blocks of igneous and meta-igneous rocks Contact—Dotted where concealed and metamorphic age (see technical discussion)] abbreviations. A location code at the end of the rock descripton gives the unit location on the map] G Jbs SHUKSAN Resistant blocks of sedimentary rocks PAYSAYTEN CORRELATION OF MAP UNITS KC High-angle fault—Dotted where concealed UNCONSOLIDATED DEPOSITS Nason Terrane MOUNT HOZOMEEN X [For mélange and metamorphic units, position of boxes with solid boundaries indicates age of assemblage Pliocene, THRUST Unconsolidated deposits Pleistocene Knmg BAKER and Holocene Nason Ridge Migmatitic Gneiss (Late Cretaceous) or metamorphism, respectively; position of boxes with dashed boundaries indicates age of protolith.] MPS (Includes Quaternary NONGLACIAL DEPOSITS ROSS —Dotted where concealed volcanoes and Miocene and Qa Alluvium of valley bottoms (Holocene and Pleistocene) THRUST STRAIGHT (or) Pliocene gravel and Kncs FAULT Chiwaukum Schist (Late Cretaceous) ROCKS OF Mount Baker (MB) at X and locally elsewhere)

LAKE Robinson Mountain (RM) UNCONSOLIDATED DEPOSITS CASCADE MAGMATIC ARC Low-angle normal fault—Dotted where concealed Qu Alluvium (Holocene and Pleistocene) ROCKS IN WENATCHEE AND CHELAN BLOCKS Ma and Pliocene WELKER GHB Flood basalt Qt Talus deposits (Holocene and Pleistocene) Terrane overlap units and stitching plutons

C Oligocene, Miocene, 1 Approximate age GLACIAL AND PK THRUST FAULT Antiformal axis and plunge—Dotted where TKsg Skagit Gneiss Complex (middle Eocene to Late Cretaceous) (millions of years) GLACIAL DEPOSITS NONGLACIAL DEPOSITS Geologic Age2 48°30’ concealed NONGLACIAL DEPOSITS ENTIAT Wi QTl Landslide deposits (Holocene, Pleistocene, and Pliocene?) CREEK Volcanic rocks Plutonic rocks QUATERNARY DARRINGTON AND TERTIARY TKso BP of the Cascade of theCascade Orthogneiss ZONE Magmatic Arc Magmatic Arc Qlh (Holocene and Pleistocene) Holocene Synformal fold axis and plunge—Dotted where 0.01 Qt Qlh T concealed TKsn Orthogneiss of The Needle Qa ROCKS OF LATE- AND POST- GLACIAL DEPOSITS Qvr Qvt Qcav OROGENIC TRANSTENSION Qu Qag Qga Qva Qgf Qud QUATERNARY - VINEGAR Qag TKto Tonalitic orthogneiss (middle Eocene to Late Cretaceous) QTl Overturned antiformal fold axis and plunge Alpine glacial deposits (Holocene and Pleistocene) Vashon stade Vashon FAULT FAULT Pleistocene DEVILS 0.55 Fraser glaciation RRP TKgo Qpf (T) Twisp Qga Deposits of alpine glaciers and Cordilleran Ice Sheet (Holocene and Pleistocene) Granodioritic orthogneiss (middle Eocene to Late Cretaceous)

0.7 H Eocene 1.6 QTog Sauk River (SR) Volcanic and Plutons of the Kt 2.4 ? QTcc Pliocene GC M sedimentary rocks of extensional event Deposits of Vashon stade of Fraser glaciation of Armstrong and others (1965) (Pleistocene) Tonalitic plutons (Late Cretaceous) FLOOD BASALT AND the extensional event 5 MOUNTAIN GF CMB Qvr Recessional outwash deposits ASSOCIATED DEPOSITS ? GLACIER Kg Granodioritic plutons (Late Cretaceous) 6 PEAK UNCONFORMITY Tyw Rocks southwest of Rocks northeast Rocks in Wenatchee Rocks in Rocks of Qvt Till Chelan Mountains terrane 12 48° QTcp FAULT and in DDMFZ Te of DDMFZ and Chelan blocks Methow block Okanogan block BMB TKns, Kns Napeequa Schist (middle Eocene to Late Cretaceous) Tyg Qva Advance outwash deposits LEVENWORTH DHP TKnu, Knu Ultramafic rock Miocene Qud Upland deposits (Holocene and Pleistocene) 19 Ch OrthogneissSkagit Gneiss Stitching Stitching plutons TKcs, Kcs stitching plutons Cascade River Schist (middle Eocene to Late Cretaceous) Helena- Complex Qgf 20 Rocks of the North- plutons Deposits of glacial outburst floods (Pleistocene) Haystack west Cascade System Pipestone Canyon melange Melange Formation MESOZOIC TKmd, Kmd Marblemount plutons (middle Eocene to Late Cretaceous) Latr Cretaceous and early Eocene Tcaf belts TERTIARY AND WINDY GLACIAL AND NONGLACIAL DEPOSITS Chelan (C) S Late 21 PASS THRUST Chelan Cretaceous Qpf Nason Swakane Cretaceous* Nonglacial and glacial sedimentary deposits older than Fraser glaciation (Pleistocene) TKmm Magic Mountain Gneiss (middle Eocene to Late Cretaceous) Wa Mountains Skykomish River (SK) terrane terrane Onlap assemblage, younger 25 terrane FAULT L marine sedimentary rocks, and t g QTog Older gravel (Pleistocene, Pliocene, and Miocene?) Swakane terrane Tcas metamorphic equivalents Kswg Plutons: Swakane Biotite Gneiss (Late Cretaceous) Tcao Early Oligocene Cretaceous* t, gneissic, tonalite ROCKS OF CASCADE MAGMATIC ARC Early

MOUNT and onlap assemblage and granodiorite; Terrane uncertain 28 47°30’ NB Cretaceous STUART Chelan Older marine g, Qcav Rocks of young (Holocene and Pleistocene) Shuksan Migmatite Rocks of the Methow Ocean sedimentary rocks Kcxm Welker Pk Late Jurassic- Tcai TERTIARY Chelan Migmatite Complex of Hopson and Mattinson (1994) (Cretaceous) FAULT Nappe Early .Cretaceous Ingalls Complex 36 ROCKS OF LATE- AND POST- W terrane Rocks of the Methow Ocean floor QTcc Caldera deposits (Pleistocene, Pliocene, and Miocene) ZONE ROCKS UNIQUE TO ROSS LAKE FAULT ZONE OROGENIC TRANSTENSION Jurassic and

Unconformity Early Cretaceous Nooksack Gneiss, schist, X Late QTcp TKrb Ruby Creek heterogeneous plutonic belt of Misch (1966) (middle Eocene to Late Cretaceous) Formation Jurassic and migmatite Intrusive rocks of Cascade Pass family (Pleistocene, Pliocene, and Miocene) MESOZOIC Middle EXTENSIONAL Jurassic Newby unit Jurassic* DEPOSITS OTHER ROCKS Shuksan AND PALEOZOIC Tcaf TKsx Skymo Complex of Wallace (1976) (middle Eocene to Late Cretaceous) Nappe Early Volcanic rocks of Fifes Peak episode (Miocene) Ingalls Early Oligocene(?) Jurassic E (W) Wenatchee terrane Ladner Group Oligocene(?) Tcas TKm, Km Metamorphosed rocks of Methow Ocean (middle Eocene to Late Cretaceous) 37 CE Intrusive rocks of Snoqualmie family (Miocene and Oligocene)

Pennsylvanian through Early Cretaceous Jurassic, Triassic, Late Eocene Snoqualmie Pass (SP) Permian, and Tcao TKmo Tonalitic orthogneiss (middle Eocene to Late Cretaceous) Pennsylvanian Volcanic and sedimentary rocks of Ohanapecosh episode (Oligocene) older(?)

40 Melange and Triassic Chelan Hozomeen Group Tcai ROCKS IN METHOW BLOCK belts Mountains Intrusive rocks of Index family (Oligocene)

El Triassic Permian, and Kpc 47° Welker Excelsior terrane Pipestone Canyon Formation (Late Cretaceous)

Tes Tev Devonian, Carboniferous, Middle Eocene Peak Nappe 0 10 20 KILOMETERS 0 5 10 MILES FLOOD BASALT AND ASSOCIATED DEPOSITS Tei Eocene Nappe Onlap assemblage and stitching plutons Te Ellensburg Formation (Miocene) 47 Ktm Tonalite plutons in Methow block (Late Cretaceous) 52 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; Trr Yakima Basalt Subgroup of Basalt Group (Miocene) Teev Early T, Twisp; W, Wenatchee; Wa, Waterville; Wi, Winthrop. Geologic features: BMB, Bald Mountain batholith; BP, batholith; CMB, Cooper Mountain batholith; DHP, Duncan Hill pluton; GC, Gamma Ridge caldera; GHB, Golden Horn batholith; HC, Hannegan Pasayten Group of Kiessling and Mahoney (1997) (Late Cretaceous) Eocene caldera; KC, Kulshan caldera; MPS, Monument Peak stock; RRP, Railroad Creek pluton. Tyw Wanapum Basalt Tees Kpv Volcanic rocks Tyg Grand Ronde Basalt Unconformity Kps Sedimentary rocks ROCKS OF LATE- AND POST-OROGENIC TRANSTENSION Rocks of Methow Ocean and onlap assemblages OROGENIC AND PRE-OROGENIC ROCKS MOSTLY WEST OF STRAIGHT CREEK FAULT OROGENIC AND PRE-OROGENIC ROCKS EAST OF STRAIGHT CREEK FAULT EXTENSIONAL DEPOSITS Ktf Three Fools sequence of Haugerud and others (2002) (Cretaceous) Tes ROCKS UNIQUE TO ROCKS UNIQUE TO ROSS Extensional sedimentary rocks (early Oligocene and Eocene) KJos Older sedimentary rocks (Early Cretaceous and Late Jurassic) WENATCHEE BLOCK ROCKS IN WENATCHEE AND CHELAN BLOCKS LAKE FAULT ZONE ROCKS IN METHOW BLOCK ROCKS IN OKANOGAN BLOCK ROCKS IN Tees Early extensional sedimentary rocks (middle and early Eocene) Rocks of Methow Ocean floor ROCKS SOUTHWEST OF DARRINGTON-DEVILS Terrane overlap units and stitching plutons KJi Tonalite intrusions (Early Cretaceous and Late Jurassic) DARRINGTON-DEVILS MOUNTAIN ROCKS NORTHEAST OF DARRINGTON-DEVILS Swakane Terrane Teev Silver Pass Volcanic Member of Swauk Formation MOUNTAIN FAULT ZONE FAULT ZONE MOUNTAIN FAULT ZONE Skagit Gneiss Complex Chelan Mountains terrane terrane uncertain Geologic Age Jnb Newby Group of Mahoney and others (2002) (Late Jurassic) Tev Volcanic rocks (early Oligocene and Eocene) TKsg TKso TKsn TKto TKgo TKmm TKhg Northwest Cascades System Jnbm Metamorphic rocks of McClure Mountain OTHER ROCKS TKhm TKns TKcs TKmd Tei Intrusive rocks (middle Eocene) Jl Rocks of the TKrb Ladner Group of Mahoney (1993) (Middle Jurassic) Eocene and TKm TKwb Okanogan terrane CENOZOIC TKebg (or) Cretaceous Welker Peak and Excelsior Shuksan Nappe TERTIARY AND AND Trr Raging River Formation (middle and early? Eocene) Hozomeen terrane TKeb CRETACEOUS MESOZOIC h Hozomeen Group (Mesozoic and Paleozoic) TKwg Middle OROGENIC AND PRE-OROGENIC ROCKS MOSTLY WEST OF STRAIGHT CREEK FAULT Kswg 73 Jurassic ROCKS IN OKANOGAN BLOCK TKnu Km Kpc ROCKS SOUTHWEST OF DARRINGTON-DEVILS MOUNTAIN FAULT ZONE Kswg TKsx Okanogan terrane TKwb Rocks of western mélange belt (middle Eocene to Late Cretaceous) Ktd Tonalite and diorite (Late Cretaceous) Nason terrane TKwg Quartz Mountain stock (Middle Jurassic) Knu Kog Granite and granodiorite (Early Cretaceous) Pasayten Ktm Ktd Knmg Kcs Group TKeb Rocks of eastern mélange belt (middle Eocene to Late Cretaceous) 90 Kt Kg Late Cretaceous Kor Remmel batholith (Early Cretaceous) Kmd Kps Kpv

middle Eocene to Late Cretaceous TKebg Migmatitic gneiss Kns Kcxm Kot Older tonalite (Early Cretaceous) TKmo TKm assemblage Onlap and stitching plutons stitching and CRETACEOUS KJya Kncs Three Fools ROCKS IN DARRINGTON-DEVILS MOUNTAIN FAULT ZONE sequence KJh Hornblendic metamorphic rocks (Early Cretaceous and Jurassic) Helena-Haystack mélange (middle Eocene and (or) Late Cretaceous) Ktf KJts Kog TKhm Serpentinite KJog Mylonitic granodiorite, gneissic trondhjemite, and banded gneiss (Early Cretaceous and Easton terrane Older Jurassic) Late Jurassic

Cretaceous to Kcxm sedimentary TKhg Blocks of resistant rock KJv Early TKwb Ket Ked Kes Kncs rocks assemblages onlap EXPLANATION OF MAP SYMBOLS Early Early Kor Kot Cretaceous KJos ROCKS NORTHEAST OF DARRINGTON-DEVILS MOUNTAIN FAULT ZONE Cretaceous Cretaceous Rocks of Methow Ocean and Ocean Methow of Rocks KJh KJog KJb Ingalls terrane GEOLOGIC SYMBOLS TKwg MESOZOIC and Jurassic KJi Northwest Cascade System Jbi Qud

Early Cretaceous Jis Contact—No contact where approximately located or gradational (mostly unit )

Jnb Jnbm and Jurassic KJn Jbs Early Cretaceous Rocks of Autochthon Fault—Dotted where concealed Early Cretaceous and Late Jurassic KJn Nooksack Formation (Early Cretaceous to Middle Jurassic) Ket Ked Kes Jbi Jis

Middle Jl High-angle fault Jurassic Jbs Jnw Middle Jurassic JURASSIC Wells Creek Volcanic Member Thrust fault Hozomeen Welker Peak and Excelsior Nappes 156 terrane KJb Jnw River terrane Bell Pass mélange (Cretaceous to Late Jurassic) Low-angle fault—Extensional fault TKhg ? KJya Yellow Aster Complex of Misch (1966) (Paleozoic or older protolith age) GEOGRAPHIC SYMBOLS TKhm KJb J^c Town KJts Kcs Kns Kmd TKmm Twin Sisters Dunite of Ragan (1961, 1963) 220 TKeb Triassic Late

Early Jurassic and Major highway TRIASSIC KJv

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

Jurassic,Triassic, Road ? floor Ocean Methow of Rocks Chilliwack River terrane Late Paleozoic to Middle Jurassic Jc KJv Cultus Formation of Brown and others (1987) (Early Jurassic and Late Triassic) Trail Permian PDc PERMIAN AND PALEOZOIC PENNSYLVANIAN PDc Chilliwack Group of Cairnes (1944) (Permian, Carboniferous, and Devonian) River Permian, Carbon- 1 Shuksan Nappe Water boundary—Blue boundary shown at edge of lake, or large river From time scale of Cowie and Bassett, 1989; Berggren and others, 1985. iferous, and Devonian PALEOZOIC 2 KJya Easton terrane See Description of Map Units for specific unit age assignment. AND OLDER Glacier or Ket Tonalite gneiss of Hicks Butte (Early Cretaceous) Mountain or peak Easton Metamorphic Suite Park, wilderness, recreation area, or scenic highway boundary Ruth Mountain Ked Darrington Phyllite (Early Cretaceous) Topographic map (1:100,000 scale) boundary—Name [abbreviation] of topographic map Kes Shuksan Greenschist (Early Cretaceous) labeled along east and west edges of map

Three Fools Peak Eldorado Hozomeen Gunn Mount Grotto Peak Mountain Peak

Figure 13. Beds of sandstone (Eocene Swauk Formation) in older extensional deposits Figure 14. Disrupted sandstone, greenstone, and light-colored dikes in argillite matrix of Figure 15. View east from Mount Index [SKnw] across Skykomish River valley to Gunn Figure 16. Large lumps of erosion-resistant rock dotting serpentinite matrix of Figure 17. View of [MBse], looking northeast from divide between Sibley Figure 19. View from Mount Winthrop [RMnw] south along Cascade Crest. Well-bedded Figure 20. Hozomeen greenstone in Methow block north of Little Beaver Creek [MBne], on south side of the east ridge of Summit Chief Mountain [SKse]. western mélange belt unit TKwb, South Fork Stillaguamish River [SRsw]. and Baring peaks [SKne], underlain by large erosion-resistant tectonic slices of Helena-Haystack mélange (units TKhm, TKhg). Most lumps are greenstone or Shuksan and Marble Creeks. In foreground, metaconglomerate of late Cretaceous Cascade River sandstone of Cretaceous Three Fools Sequence (rocks of Methow Ocean) form crest. where it is probably Triassic, and on Hozomeen Mountain [MBne], where it is Late migmatitic gneiss in less-resistant sedimentary rocks of eastern mélange belt. Grotto Greenschist. View northwest from ridge southwest of Day Lake [SRnw]. Schist contains cobbles (deposited in Triassic) stretched to form streaks. Orthogneiss of Divide at right was rounded by overriding Cordilleran Ice Sheet. Mixed glacial deposits Paleozoic. View northeast from ridge south of Little Beaver Creek. Mountain is composed of granodiorite of Miocene Grotto batholith, the eroded root of a Eldorado pluton visible in background. Small glaciers and moraine deposits in valley are (drift) from ice sheet and local alpine glaciers are visible in valley bottom. Figure 12. Granite of Cascade Pass family on the west wall Cascade Magmatic Arc volcano. Mountans on skyline beyond are carved from rocks of visible behind . of Nooksack cirque in foreground. Ruth Mountain [MBnw] Nason terrane (in Wenatchee block), predominantly Late Cretaceous Chiwaukum Schist to northeast is carved from volcanic breccia of Pliocene and batholith. Foreground rock is Jurassic metagabbro, another tectonic Hannegan Caldera. Both rocks formed in the Cascade slice mixed into eastern mélange belt in latest Cretaceous or early Tertiary. Magmatic Arc. Extensive glacial moraine covers valley floor. Geologic Map of the North , Washington By Any use of trade, product, or firm names in this publication is for descriptive Ralph A. Haugerud and Rowland W. Tabor purposes only and does not imply endorsement by the U.S. Government.

2009 Digital files available at http://pubs.usgs.gov/sim/2940