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CROSS SECTION EXPLANATION

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Geologic units too thin to show as polygons at the scale of the cross section. Ticks mark separate units.

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I R O N M O U N TA I N FA U LT Z O N E

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FRASERGLACIATION

POSSESSIONGLACIATION

DOUBLE BLUFFGLACIATION

2.6 Ma

Holocene

QU

ATE

RN

AR

Y

Ple

isto

cene

TER

TIA

RY

Jurassic

Paleogene

Neogene

Cretaceous66 Ma

145 Ma

200 Ma

HAMM CREEKINTERGLACIAL INTERVAL

OLYMPIANONGLACIAL INTERVAL

WHIDBEYINTERGLACIAL INTERVAL

PRE-HAMM CREEKINTERVAL

(~60–80 ka)

(~130–190 ka)

(>300–550 ka)

(~190–245 ka)

(~80–130 ka)

(~20–60 ka)

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The pamphlet provides direct or indirect age constraints for many of the geologic units, including new IRSL ages for glacial and nonglacial deposits (Appendix A). See Morrison (1991) for Pleistocene age constraints on the glacial and nonglacial intervals. Tabor and others (1993) indicate that the Western mélange belt meta-intrusive rocks (unit KJigbw) are ~150–170 Ma and are about the same age or older than the Kimmeridgian to Valanginian (157–134 Ma) metasedimentary rocks of the belt. However, detrital zircon U-Pb ages for unit KJmsw (Dragovich and others, 2014) indicate that the metasandstone in this unit is locally as young as 74 Ma.

CORRELATION OF MAP UNITS

Glacial Geologic Units

Bedrock Geologic Units

Nonglacial Geologic Units

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Qcpf

Qcpf

Qch Qchl

121°52′30″48°07′30″

122°00′00″48°07′30″

R 6 E R 7 E

T 31 NT 30 N

02′30″ 02′30″

55′00″

55′00″

05′00″

121°52′30″48°00′00″

122°00′00″48°00′00″

57′30″

05′00″

57′30″

T 31 NT 30 N

T 30 NT 29 N

T 30 NT 29 N

R 6 E R 7 E

© 2016 Washington Division of Geology and Earth Resources

Lambert conformal conic projectionNorth American Datum of 1927; to place on North

American Datum of 1983, move the projection lines approximately 22 meters north and 92 meters east as shown by crosshair corner ticks

Base map from scanned and rectified U.S. Geological Survey Granite Falls 7.5-minute quadrangle, 1989

Shaded relief generated from a lidar bare-earth digital elevation model (available from Puget Sound Lidar Consortium, http://pugetsoundlidar.ess.washington.edu/)

GIS by Skyler P. MavorDigital cartography by Daniel E. Coe,

and Ian J. HubertLayout and production by Daniel E. Coe and

Alexander N. Steely

This geologic map was funded in part by the U.S. Geological Survey National Cooperative Geologic Mapping Program.

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Research supported by the U.S. Geological Survey, National Cooperative Geologic Mapping Program, under USGS award number G15AC00248. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

Disclaimer: This product is provided ‘as is’ without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular use. The Washington Department of Natural Resources and the authors of this product will not be liable to the user of this product for any activity involving the product with respect to the following: (a) lost profits, lost savings, or any other consequential damages; (b) fitness of the product for a particular purpose; or (c) use of the product or results obtained from use of the product. This product is considered to be exempt from the Geologist Licensing Act [RCW 18.220.190 (4)] because it is geological research conducted by or for the State of Washington, Department of Natural Resources, Division of Geology and Earth Resources.

WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCESMAP SERIES 2016-03

Geologic Map of the Granite Falls 7.5-minute Quadrangle

Pamphlet accompanies mapGeologic Map of the Granite Falls 7.5-minute Quadrangle,Snohomish County, Washington

Joe D. Dragovich, Skyler P. Mavor, Megan L. Anderson, Shannon A. Mahan, James H. MacDonald Jr., Jeffery H. Tepper, Daniel T. Smith, Bruce A. Stoker, Curtis J. Koger, Recep Cakir, S. Andrew DuFrane, Spenser P. Scott, and Benjamin P. Justman

November 2016

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MAJOR FINDINGS

• The Explorer Falls basin preserves a thick sequence of weathered Pleistocene Pilchuck River provenance alluvium that has been locally inverted due to on-going regional north-south compression.

• We suggest that the Pilchuck River anticline is a mid-to late-Pleistocene growth fold in the northern part of the Explorer Falls basin—this fold is directly south of the locally active Carpenter Creek fault (CCF) and generally above the Carpenter Creek earthquake cluster (CCEC).

• The northwest-trending right-lateral to oblique-slip Granite Falls fault zone (GFFZ) forms the eastern edge of the Bosworth Lake basin, which is a small, eastern arm of the greater Everett basin.

• The Granite Falls stock is the source for numerous dikes and the sub-volcanic magmatic rhyolites in the map area. The stock is thought to have intruded into a “pull-apart” or extensional structure during regional Eocene transtension.

• Widespread ultramafite within and west of the GFFZ may mark the lowermost thrust of the Eastern mélange belt (EMB) over the Western mélange belt (WMB). Additionally, stratigraphically coherent low-grade metasediments of the WMB were locally mapped east of the GFFZ in the quadrangle.

• Our array of portable seismic instruments deployed around the CCEC has detected micro and minor earthquakes along an east-northeast-trending band that we correlated broadly with the CCF. However, they likely include smaller strains along conjugate faults to the CCF that were generated by earlier larger CCF seismic events.

DESCRIPTION OF MAP UNITS(see pamphlet for detailed map unit descriptions and Table 1 for sand provenance information) Quaternary Sedimentary Deposits

HOLOCENE NONGLACIAL DEPOSITS

Peat—Loose or soft peat, muck, and organic silt and clay, locally with diatomite and thin beds of Mazama ash (Rigg, 1958). Peat is found in abandoned river-channel depressions where it is interstratified with alluvial deposits (for example, in the South Fork Stillaguamish River valley) or deposited in upland depressions and kettles over low-permeability glacial deposits such as till or poorly sorted ice-contact deposits.

Alluvium—Sand, silt, gravelly sand, and sandy pebble gravel; locally includes peat and organic sediment and (or) cobble gravel; clasts subrounded to rounded; well stratified and sorted; sand is planar bedded; woody debris and detrital wood are common.

Landslide deposits (Holocene to latest Pleistocene)—Diamicton (unsorted mixture of clay, silt, sand, gravel, and wood debris) or boulder gravel, and local, minor, amounts of sand or gravel. Only large landslides are shown; absence of a mapped landslide does not imply absence of hazard.

Alluvial fan deposits (Holocene to latest Pleistocene)—Diamicton, alluvial gravel, boulder gravel, and sand; poorly to moderately sorted; moderately stratified to massive; locally contain significant debris flow deposits.

PLEISTOCENE GLACIAL AND NONGLACIAL DEPOSITSDeposits of the Vashon Stade of the Fraser GlaciationVashon Recessional Deposits

Vashon recessional glaciolacustrine (glacial lake) deposits—Silt and clayey or sandy silt to silty sand, typically with scattered dropstones; local lenses or beds of sand or gravel; loose or soft; massive or laminated to thinly bedded; locally displays varve-like rhythmites; deposited in proglacial lakes.

Vashon outwash sand—Sand and pebbly sand with some interbeds of silty sand, silt, or gravel; loose or soft; unstratified to weakly stratified to planar bedded, laminated, and rarely crossbedded.

Vashon deltaic outwash and kame deltas—Sandy cobble gravel, gravel, pebbly sand; loose; moderately to well sorted; thin to very thickly bedded; well stratified with conspicuous high-amplitude foreset beds.

Vashon fluvial outwash deposits—Cobble and boulder gravel, gravel, pebbly sand, and interbeds of sand and rare silt; loose; moderately to well stratified; commonly contains medium to very thick subhorizontal beds with bar or ripple crossbedding, imbricated gravel, scour structures, and rip-up clasts.

Vashon ice-contact deposits—Cobble to boulder gravel and gravel, locally containing diamicton, silty pebble gravel, sand, pebbly sand, and silt; loose or soft; moderately stratified and medium to very thickly bedded; abrupt grain-size changes common. Locally subdivided into:

Vashon ice-contact kames—Cobble and boulder gravel, gravel, sand, and pebbly sand, with lenses of diamicton; loose; crossbedded, with localized oversteepened or slumped strata; cut-and-fill structures and rip-up clasts of till or silt common.

Vashon outwash gravel deposits, undivided—Poorly exposed boulder–pebble gravel to pebbly sand; loose; massive to crudely bedded; largely ice-contact deposits; may include any of the gravelly Vashon recessional facies.

Vashon Advance Proglacial and Subglacial Deposits

Vashon lodgment till—Diamicton (unsorted mixture of clay, silt, sand, and gravel); matrix-supported; dense; accreted at the base of the Vashon ice; typically displays a friable shear fabric.

Vashon advance outwash deposits—Sand and pebble gravel, sand and cobble gravel, and local silt; dense; well sorted and stratified; thinly to thickly bedded; deltaic and bar foreset beds, cut-and-fill structures, and silt rip-up clasts common.

Vashon advance glaciolacustrine deposits—Silt, clayey silt, pebbly silt, and diamicton; stiff to hard, or dense to very dense; locally contains very thin to thick beds of sand, scattered dropstones, and iceberg melt-out or flow till; stratification and sorting vary; massive to thinly bedded, laminated, or varved.

Pre-Fraser Glacial and Nonglacial Deposits

Pre-Fraser continental nonglacial deposits, ancient Pilchuck River facies, undivided (Pleistocene)—Sand, silt, or clay, locally with some organic matter and peat, and less sand and gravel; deposited prior to the Fraser glaciation; sand is typically weathered to a yellow-brown-gray; dense; laminated to very thickly bedded and mostly well stratified; may contain charcoal, logs, sticks, disseminated organic matter, trough-and-ripple crossbedding, and graded beds.

Whidbey Formation, ancient Pilchuck River valley facies (Pleistocene)—Sand, silt, clayey silt, and silty sand with less pebbly sand, clay, gravel, and (or) organic sediment (including peat); dense or hard; well sorted and stratified; may contain charcoal, disseminated organic matter, trough-and-ripple crossbedding, graded beds.

Hamm Creek nonglacial interval (formation), Pilchuck Valley provenance (Pleistocene)—Sand, silt, and silty sand, with less pebbly sand, lenses or beds of gravel, clay, and (or) organic sediment with disseminated organic material, wood, charcoal, and plant fossils; sand is weathered to a distinctive bright orange-brown; dense or hard; well sorted and stratified; mostly occurs as laminated to thinly bedded sand and silt, locally with crossbedding or graded beds; rare folded or chaotic bedding.

Hamm Creek nonglacial deposits, locally derived facies (Pleistocene)—Pebbly sand, sand, with less gravel, cobble gravel, and rare silt; locally contains organic sediments; distinctive dark-bluish gray, weathers grayish brown; dense or hard; thinly to thickly bedded, commonly with lenticular interbeds; low-angle foreset beds rarely observed; well sorted; angular to subrounded grains. These deposits are very lithic rich and contain 50–60 percent WMB-derived metasedimentary grains—meta-argillite, phyllite, metasandstone, and metachert.

Pre-Hamm Creek nonglacial deposits, ancient Pilchuck River facies (Pleistocene)—Pebble gravel, gravelly sand, pebbly sand, sand, silty sand, and silt , locally with some cobble gravel and clay; dense or hard; sand is typically yellowish brown to pale brown, but sometimes grey to blue grey; oxidized and strongly weathered; thin to very thickly bedded; well stratified; rip-up clasts, cross bedding, graded beds, leaves, twigs, charcoal, logs, or disseminated organic matter are common; flame structures are found in a few outcrops.

Pre-Hamm Creek continental deposits, locally derived facies—Sand, pebbly sand, sandy pebble gravel, with less gravel, cobble gravel, and rare silt; locally contains peat, logs or organic sediment; dense or hard; sediment has a distinct local Western mélange belt provenance with up to 95 percent WMB-derived metasedimentary grains—meta-argillite, phyllite, metasandstone, and metachert.

Pre-Fraser glacial and nonglacial deposits (Pleistocene to Pliocene?)(cross sections only)—Gravel, boulder gravel, sand, silt, clay, and diamicton; may locally contain peat or organic sediments. This unit is mapped in cross section where pre-Fraser deposits may include older glacial and (or) nonglacial material.

TERTIARY VOLCANIC, INTRUSIVE, AND SEDIMENTARY ROCKS

Rocks of Bulson Creek of Lovseth (1975)(Oligocene to Eocene)—Lithic to lithofeldspathic sandstone with less conglomerate, siltstone, and coal with minor claystone. Units …Ec and …En thicken considerably west of the Granite Falls fault zone and into the Bosworth Lake basin.

Rocks of Bulson Creek of Lovseth (1975), nearshore to marine facies (Oligocene to Eocene)—Shale, siltstone, sandstone, and mostly pebble conglomerate. Subsurface information indicates a substantial thickness of unit …En in the sorthwestern corner of the map area directly west of the Granite Falls fault zone.

Rhyolite of Hansen Lake (Eocene)—Dacitic to rhyolitic ash-flow tuff, lapilli tuff, lapillistone, tuff breccia and flows; glassy to devitrified; medium-potassium calc-alkaline; fragmental tuff and breccia deposits typically dominated by lithic fragments.

Granite Falls stock, main-phase intrusive complex (Eocene)—Light to dark-grey hornblende granodiorite; hypidiomorphic granular; medium-potassium calc-alkaline; locally grades to minor quartz gabbro near contact complexes along the margins of main phase intrusions.

Granite Falls stock, contact complex and dikes (Eocene)—Contact complex containing medium- to high-K calc-alkaline dacite and rhyolite dikes with lesser andesite and basaltic trachyandesite; locally includes fine-grained to medium-grained gabbro and minor granodiorite bounding the Granite Falls stock (main phase). Also includes solitary dikes and dike complexes intruding fault zones away from the main stock as well as thicker contact complexes bounding the main stock.

MESOZOIC LOW- TO MEDIUM-GRADE METAMORPHIC ROCKS

Western mélange belt of Frizzell and others (1987), undivided (Cretaceous to Jurassic)(cross sections only)—Meta-argillite, metasandstone, greenstone, metachert, with less metadiabase, metagabbro, metatonalite (metatrondhjemite), slate, (banded) amphibolite and hornblendite, and phyllite; minor marble with metaquartz-diorite and rare ultramafic rocks. Subdivided into:

Metavolcanic rocks (Cretaceous to Jurassic)—Greenstone; derived from metamorphosed basaltic to andesitic tuff, tuff breccia, and lapilli tuff with basaltic to dacitic volcanic flows.

Metasedimentary rocks (Cretaceous to Jurassic)—Marine feldspathic to feldspatholithic subquartzose metasandstone, silty metasandstone, meta-argillite, metatuff, tuffaceous metasandstone, and chert-pebble metaconglomerate; lesser metachert and marble found as discontinuous pods. Marble pods might be tectonically emplaced.

Phyllite (Cretaceous to Jurassic)—Phyllite, phyllitic metasandstone, meta-argillite, slate, and minor amounts of semischistose rocks, including local foliated metatuffaceous greenschist interbeds. Includes rare tectonic lenses quartz mica schist.

Metagabbro (Cretaceous to Jurassic)—Metagabbro, quartz metagabbro and minor metadiabase dikes or rare zones of felsic pegmatite; regionally, lesser amounts of metatrondhjemite/metatonalite, feldspathic hornblendite and gneissic amphibolite, and rare meta quartz-diorite are reported regionally.

Ultramafic rocks (Cretaceous to Jurassic)—Serpentinite with rare serpentinized peridotite or pyroxenite.

Listwänite silica-carbonate rocks (Cretaceous to Jurassic)—Silica-carbonate mineralization products (listwänites) locally contain pods of incompletely altered serpentinite and intense secondarily brecciated silica-carbonate rock.

HOLOCENE TO TERTIARY TECTONIC ZONES

Tectonic zone—Cataclasite, fault breccia, clay-rich fault gouge, protomylonite, and moderately to strongly slickenlined, fractured, and veined rocks in fault zones; green and yellow to orange to variously colored, mottled, and locally altered.

GEOLOGIC SYMBOLS

Contact—Solid where location accurate; long-dashed where approximately located; queried where identity or existence questionable

Fault, unknown offset—Solid where location accurate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable

Thrust fault—Solid where location accurate; short-dashed where inferred; dotted where concealed; triangles on upper (structurally higher) plate

Right-lateral strike-slip fault—Solid where location accurate; dotted where concealed; queried where identity or existence questionable; arrows show relative motion

Reverse left-lateral, oblique-slip fault—Short-dashed where inferred; dotted where concealed; queried where identity or existence questionable; arrows show relative horizontal motion

High-angle dip-slip fault—Short-dashed where inferred; dotted where concealed; queried where identity or existence questionable; U, upthrown block; D, downthrown block

High-angle, oblique-slip fault—Solid where location accurate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable; arrows show relative horizontal motion; U, upthrown block; D, downthrown block

Anticline—Solid where location accurate; short-dashed where inferred; dotted where concealed; queried where identity or existence questionable

Syncline—Solid where location accurate; short dashed where inferred; dotted where concealed; queried where identity or existence questionable

Fluvial terrace scarp—Identity and existence certain; location accurate; hachures point downslope

Landslide scarp—Identity and existence certain; location accurate; hachures point downslope

Cross section line

Direction of downslope movement of landslide

Inclined bedding—showing strike and dip

Vertical bedding—showing strike

Horizontal bedding

Inclined bedding in unconsolidated sedimentary deposits—showing strike and dip

Inclined foreset bedding in unconsolidated sedimentary deposits—showing strike and dip

Inclined bottomset bedding in unconsolidated sedimentary deposits—showing strike and dip

Inclined metamorphic or tectonic foliation—showing strike and dip

Vertical metamorphic or tectonic foliation—showing strike

Vertical metamorphic or tectonic foliation parallel to bedding—showing strike

Inclined first-generation metamorphic or tectonic foliation—showing strike and dip

Inclined second-generation metamorphic or tectonic foliation—showing strike and dip

Inclined mylonitic foliation—showing strike and dip

Inclined crenulation lineation—showing bearing and plunge

Inclined flow banding, lamination, layering, or foliation in igneous rock—showing strike and dip

Inclined fold hinge of small, minor fold—showing bearing and plunge

Small, minor inclined joint—showing strike and dip

Small, minor vertical or near-vertical joint—showing strike

Slickenside—showing strike and dip

Vertical slickenside—showing strike

Inclined slickenline, groove, or striation on fault surface—showing bearing and plunge

Small fault or shear—showing strike and dip

Small fault or shear, vertical—showing strike

Age site, fossil

Age site, potassium-argon (K-Ar)

Age site, uranium-lead (U-Pb)

Age site, luminescence (OSL and (or) IRSL)

Water well

Significant site

Geophysical data collection site

Drill hole or test pit