A

B

C'

A'

B'

C

QTc

QTc

QTc

QTc

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls Qls

Qls

Qls

Qa

Twfsh

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Qls

Tt Tt

QTfg

Qls?

Ttfc

Ttfc

Ttfc

Ttfc

Ttfc Ttfc

Ttfc

Ttfc

Ttfc

Ttfc

Ttfc

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

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Qa

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Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Tlkt

Ttfh

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qlo Qlo

Qlo

Qls

Qls

Qls

Qa

Qa

Qa

Qa Qt

Qt

Qt

Qt

Qt

Qt

Qt

Ttfh

Ttfh Ttfh

Ttfh

Qfs

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Ttfh

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qac Qac

Qac

Qac

Qac

Qac

Qac

Qac

Qtdl

Tvs

Tvs

Tvs

Qtds1

Twfsh

Twfsh

Twfsh Twfsh

Twfsh

Qtds2

Qtds2

Qtds2

Qtds2

Qtds2

Qtds2

Twfss

Twfss

Qbbv

Qtds3

Qtds3

Twprr

Qbch

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

Qtdwl

af

af

af

af

af

af

af

Qa

af

Qtdwu

Qtdwu

Qtdwu Qtdwu

Qtdwu

Ta

Ta

Ta

Ta

Ta Ta

Ta

Twfsh

Twfss

Twfsh

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Tbem

Qe Qe

Qe

Qe

Qe Qe

Qfg

Qfg

Qfg

Qfg

Tlkt

Tlkt

Tlkt

Tlkt

Tlkt

Qfs

Qfs

Qfs

Qfs

Qfs

Qfs

Tob

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Qh

Tsr

Tsr

Tsr

Tsr

Tsr

Tsr

Tsr

Qlo

Qlo

Qlo

Qlo

Qlo

Tsr?

Qtds3

Ttfh

Ttfh

Ttfh

Ttfh

Qfg

Qac

Qac

Ttfc

Ttfc

Ttfh

Qmbb

Twprr

Qls

Qmbb

Qmmn

Qmbp

Qmpm

Tgsb

QTc

RIVER

FAULT

LACAMAS

LAKE

FAULT

BLUE

LAKE

FAULT

SANDY

A

8

7

6

5

4 3

2

1

15

14

13

12

11

10

9

1.53±0.39 Ma

2,284±16 ka

1,292±19 ka

1,159±14 ka

693±9 ka

8

7

6

5

4

3

2

1

52

53

52

51

50

49

48 47

45 46

43

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34

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9

2

3

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41

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26 18

20

25

9

14

84 30

140

River

RIVER

CAMAS

Washougal

WASHOUGAL

WASHOUGAL

RIVER

SANDY

Broughton

Bluff

TROUTDALE

LARCH MOUNTAIN QUAD.

Little

LACAMAS

CREEK

QUAD.

SANDY QUAD.

45 37'30"

45 30'00"

122 22'30" 122 15'00"

CAMAS

QUAD.

Creek

Beaver

Chamberlain

Hill

Crown

Point

Island

Woodburn

Hill

Nichols

Hill

Mount

Norway

Creek

Lawton

Creek

Gibbons

Creek

Walton

Creek

Campen

Reed Gary I.

Island Flag

Creek

Smith

Creek

Big

Creek

Pounder

Canyon

Howard

Chanticleer

Point

Corbett

Springdale

BRIDAL

VEIL

QUAD.

RIVER

COLUMBIA

OREGON

WASHINGTON

CLARK CO

MULTNOMAH CO

Creek

Gordon

Buck

Creek

Creek

Winkler

Historic

Columbia

River

Hwy

Index map showing geographic and cultural features of the Washougal 7.5' quadrangle

and vicinity on hillshade image derived from 10-m DEM.

122o22'30"

45o30'

122o15''

122o22'30" 122o15'

45o30' 

45o 45 37'30" o37'30"

T 2 N

T 1 N

R3E R4E 

17' 30" 1 550 000 FEET (WASH.)

550 552 553 554 556 557

5039000mN

5041

5042

5043

5045

5046

5047

5048

5049

5050

553 554 555 556

5052000mN

5050

5048

5047

5046

5045

5044

5043

5042

5041

(DAMASCUS)

(SANDY) (BULL RUN) (BRIDAL VEIL)

(BOBS MOUNTAIN)

(LARCH MOUNTAIN)

(LACAMAS CREEK)

(CAMAS)

20' 1 520 000 FEET (WASH.) 17'30" 

32'30"

35'

32' 30"

35'

T 1 N

T 1 S

557

5051

T 2 N

1 550 000 FEET (OREG.) 

5049

5039

710 000 FEET

 (OREG.) 

 

70 000 FEET

 (WASH.) 

 

555

5040

110 000 FEET

(WASH.)

549000mE 1 530 000 FEET (OREG.) 558

5040

5051

680 000 FEET (OREG.) 

T 1 N

20'

551

550 551

Scientific Investigations Map 3257

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

1

U.S. Geological Survey, 2Groundwater Solutions, Inc.

Geologic Map of the Washougal Quadrangle, Clark County, Washington, and Multnomah County, Oregon

By

Russell C. Evarts1, Jim E. O’Connor1, and Terry L. Tolan2

2013

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

This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary 

between electronic plotters and between X and Y directions on the same plotter, and paper may change 

size due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map.

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/3257/

Suggested Citation: Evarts, R.C., O’Connor, J.E., and Tolan, T.L., 2013, Geologic map of the Washougal 

quadrangle, Clark County, Washington, and Multnomah County, Oregon: U.S. Geological Survey 

Scientific Investigations Map 3257, scale 1:24,000 [http://pubs.usgs.gov/sim/3257/].

af

A

5

DESCRIPTION OF MAP UNITS

SURFICIAL DEPOSITS

Artificial fill (Holocene)—Unconsolidated soil, sand, gravel, 

and crushed rock used for highway and railroad beds, 

levees, and small dams

Eolian deposits (Holocene)—Unconsolidated, well-sorted 

sand forming small dunes cresting as high as 5 m above 

adjacent floodplain level along Columbia River. Composed of fine to coarse, micaceous quartzofeldspathic 

sand of Columbia River provenance. Position on Columbia River floodplain deposits indicates dunes less than 

2–3 ky old. Historically active but now mostly vegetated 

and stable owing to circa 1940s diminishment of sand 

supply from beaches and sand bars flanking Columbia 

River that were more frequently exposed prior to flow 

regulation

Alluvium of Columbia River floodplain and channel 

(Holocene)—Unconsolidated fine sand, silt, and clay that 

underlies historic floodplain, islands, and bars of the 

Columbia River at elevations less than 30 ft (10 m); composed largely of quartz, feldspar, and conspicuous muscovite. Near tributary mouths, unit includes rare lenses of 

cobble to pebble gravel composed largely of wellrounded clasts reworked from Troutdale Formation; also 

includes local unmapped areas of dredge spoils and other 

fills, and possibly eolian deposits. Sections exposed in 

banks, excavations, and drill-core samples commonly 

show sand-silt couplets as thick as 30 cm; basal sands 

locally display ripple cross lamination, planar lamination, 

and tabular foresets; capping silt and clay beds generally 

massive and bioturbated; couplets interpreted as deposits 

of large Columbia River floods before substantial 20th 

century river regulation and floodplain diking. Unit 

includes local diatomaceous beds and layers of organicrich sediment that probably formed in floodplain 

marshes, ponds, and lakes, as well as thin (<2 cm) tephra 

beds from Holocene eruptions of Mount St. Helens. 

These deposits resulted from river aggradation since the 

last glacial sea-level low stand at about 15 ka (Baker, 

2002); locally extends to 300 ft (90 m) below sea level in 

the map area (Hoffstetter, 1984; Hartford and McFarland, 

1989; Gates, 1994; Pratt and others, 2001; Rapp, 2005). 

Consistent with this, in the adjacent Camas quadrangle, 

alluvium of the Columbia River contains fluvially 

concentrated 7.7-ka Mazama tephra (Gates, 1994) at 45 ft 

(14 m) below sea level. Regionally, most deposits above 

modern low-water river level (3 ft (1 m) above sea level 

in map area) are younger than 2,000 years old and most 

dated deposits forming Reed Island are less than 500 

years old

Alluvium (Holocene and Pleistocene)—Unconsolidated 

sand, gravel, and organic-rich mud along rivers and 

creeks and in seasonally inundated depressions. Deposits 

along Washougal, Little Washougal, and Sandy Rivers 

consist mostly of st ratified sand and cobble to pebble 

gravel; deposits along smaller watercourses are more 

variable. Known thicknesses everywhere less than 10 m. 

Holocene alluvium along the Sandy River post-dates late 

18th-century Old Maid eruptive period from Mount Hood 

(included in Qh)

Talus deposits (Holocene and Pleistocene)—Unsorted accumulations of large angular basalt blocks below cliffs 

composed of Quaternary lava flows (Qmmn and Qmbb) 

north of Mount Norway and near Broughton Bluff; 

include post-landslide rockfall deposits at base of headwall scarps

Landslide deposits (Holocene and Pleistocene)—Diamicts 

of unsorted, angular bedrock and surficial material transported downslope en masse. Chiefly deep-seated, semicoherent slumps and internally disrupted rockslide, earthflow, and debris-flow deposits. Many mapped slides head 

at arcuate scars and exhibit subhorizontal tops, bulbous 

toes, and hummocky, poorly drained surfaces. Large 

landslide complexes developed along Washougal River 

and east of Chanticleer Point where Pliocene and Quaternary lava flows overlie deeply weathered Troutdale 

Formation or Columbia River Basalt Group

Deposits derived from the Mount Hood volcano 

(Holocene)—Unconsolidated, stratified sand and gravel 

and diamictons composed of volcanic debris transported 

down Sandy River from Mount Hood; underlie an extensive lowland north of Broughton Bluff informally known 

as the Sandy River delta. As thick as 25 m in lower Sandy 

River valley (Pierson and others, 2009) and 9 m in Sandy 

River delta where locally interbedded with Columbia 

River overbank deposits and almost everywhere overlain 

by as much as 1 m of more recent Columbia River floodplain deposits (Rapp, 2005). Sand and gravel form planar 

or cross-stratified beds that typically fine upwards; gray 

except for fine sand beds, which are locally red to pinkish. 

Gravel clasts are dominantly fresh, porphyritic, pyroxene 

and hornblende andesites; sand composed mostly of angular to sub-rounded, gray to red lithic (andesite) fragments, 

5–20 percent clear plagioclase fragments, and 2–10 

percent equant hornblende crystals. Diamictons are brown 

to brownish gray, massive to weakly stratified beds, 0.5 to 

5 m thick, composed of 30–50 percent angular andesite 

fragments to 10 cm diameter in matrix of sand, silt, clay, 

and wood (Rapp, 2005). Numerous radiocarbon ages and 

regional stratigraphic relations show that these deposits 

are younger than 1,600 years old. Stratified sand and 

gravel interpreted to represent fluvial aggradation 

triggered by highly increased sediment supply following 

Mount Hood eruptions. Diamicts are interpreted as deposits of Mount Hood lahars produced in conjunction with 

eruptive activity. Deposits were chiefly formed during and 

after the Timberline and Old Maid eruptive episodes of 

Crandell (1980); diamictons and stratified sands older 

than 800 years are related to the Timberline period, which 

began about A.D. 400 (Rapp, 2005; Pierson and others, 

2009). Timberline-age deposits underlie much of the 

Sandy River delta and aggraded the lower Sandy River 

valley within the map area by as much as 25 m (Pierson 

and others, 2009). Post-A.D. 1780 (Pringle and others, 

2002; Pierson and others, 2010) Old Maid-age deposits 

form stratified sand and gravel aggradation sequences as 

thick as 23 m in the Sandy River valley, overtopping and 

burying much of the Timberline-age deposits; they also 

form several channel-fill deposits, as thick as 5 m, in the 

Sandy River delta (Rapp, 2005)

Loess (Holocene and (or) Pleistocene)—Massive unconsolidated deposits of light-gray to buff, micaceous, quartzfeldspathic eolian silt and fine sand; commonly contains 

isolated granules and small pebbles; locally capped with 

strongly developed red soils, especially on higher uplands. 

Forms widespread mantle to 25 m thick on upland south 

of Columbia River. Less-weathered accumulations mantle 

flatter surfaces along south side of Columbia River valley 

near Corbett Station. Overlies 970-ka basaltic andesite of 

Broughton Bluff (Qmbb); probably deposited during 

several episodes throughout late Quaternary time; 

includes Holocene accumulations closer to the Columbia 

River

Sandy River terrace deposits (Holocene and 

Pleistocene)—Fluvial gravel and sand forming sets of 

terraces in Sandy River valley; include Mount Hood lahar 

deposits. Divided into three units based on differences in 

tread elevations and weathering characteristics

Terrace deposits 1 (Holocene and Pleistocene)—Poorly 

exposed, unconsolidated, sandy cobble to boulder gravel to 

20 m thick underlying terrace surfaces at elevations 

between 160 and 190 ft (50 and 60 m) along Sandy River. 

Consist of subhorizontal gravel sheets, 0.5 to 5 m thick, 

locally separated by thin sand lenses; poorly sorted, locally 

imbricated, and varies from compact clast-supported 

cobble and boulder gravel with sand matrix to loose openwork cobble gravel; subangular to well-rounded clasts 

include common large (to 1 m diameter) boulders of hornblende andesite. Deposit contains at least one 1-m-thick 

bed of silty lithic-rich sand inferred to be the distal facies of 

a Mount Hood lahar. Exhibits weakly developed soil 

profile and weathering rinds on fine-grain volcanic clasts 

<1 mm thick, suggesting relative youth. Not covered by 

Missoula-flood deposits so must postdate 20- to 15-ka 

cataclysmic flooding. Thermoluminescence analysis on the 

lithic-rich sand gave an age of 14.3±1.2 ka, consistent with 

deposition after the Missoula floods. Presence may reflect 

deposition behind the immense Missoula flood bar extending southwestward of Broughton Bluff (Evarts and 

O’Connor, 2008) that temporarily blocked the Sandy River 

at its confluence with the Columbia River. Equivalent to 

Sandy River terrace deposits (Qtds) mapped in adjacent 

Camas quadrangle (Evarts and O’Connor, 2008) and 

equivalent in part to Estacada Formation of Trimble (1963)

Terrace deposits 2 (Pleistocene)—Unconsolidated sandy 

gravel underlying distinct benches along the Sandy River 

valley; as thick as 20 m but only exposed along steep 

valley slopes and in cuts along roads and tracks descending 

to valley bottom. Consists of subhorizontal gravel sheets, 

0.5–5 m thick, locally separated by thin sand lenses; poorly 

sorted, locally imbricated, minimally weathered; varies 

from compact clast-supported boulder and cobble gravel 

with sand matrix to loose open-work cobble gravel; subangular to well rounded clasts include common large (to 1 m 

diameter) boulders of hornblende andesite, especially near 

base. Overlies hyaloclastic sandstone member of the 

Troutdale Formation (Ttfh) at elevations between 140 and 

205 ft (40 and 60 m). Everywhere overlain by fine-grained 

Missoula-flood deposits (Qfs) at elevations between 165 

and 245 ft (50 and 75 m). Locally capped at southern end 

of map area by <3 m of horizontally bedded feldspar- and 

lithic-rich sand and angular andesite gravel supported by 

silt and sand matrix; inferred to represent lahar and laharrunout deposits, probably from Mount Hood eruptions, and 

probably correlative to similar but thicker volcanogenic 

sequences south of map area (J.W. Vallance and J.E. 

O’Connor, unpub. mapping). Age uncertain, but lack of 

weathering at contact with overlying fine-grained 

Missoula-flood silt (Qfs) indicates that, in part, the unit 

closely pre-dates the 20–15 ka Missoula Floods; optically 

stimulated luminescence ages from correlative deposits 

south of the map area range from >155 ka to 22.4±2.5 ka. 

Distribution and composition of unit indicate deposition 

during Sandy River aggradational phase, likely in part 

coinciding with late Wisconsin (30–20 ka) glaciation of 

Mount Hood region and late last-glacial eruptive events at 

Mount Hood. Corresponds in part to the Estacada Formation as defined and mapped by Trimble (1963), but probably older than the 14- to 12-ka Clackamas River gravel 

(Wampler, 2004) that composes the type section of the 

Estacada Formation. Equivalent to ancestral Sandy River 

alluvium (Qaas) mapped in adjacent Camas quadrangle 

(Evarts and O’Connor, 2008)

Terrace deposits 3 (Pleistocene)—Weathered and unconsolidated sandy gravel underlying terraces and uplands 

along the Sandy River; forms deposits as thick as 35 m that 

underlie dissected benches with surfaces as high as 540 ft 

(165 m) elevation. Composed of sandy bouldery cobble 

gravel in poorly sorted, clast-supported beds to 5 m thick 

with lenses of gray silty coarse sand. Some beds contain 

abundant subrounded clasts, as large as 1 m across, of 

Mount Hood-derived hornblende andesite; other common 

clast types include light-gray, olivine-phyric, Pliocene to 

Pleistocene basaltic rocks, andesites eroded from the 

Rhododendron Formation, and dark-gray to black aphyric 

rocks of the Columbia River Basalt Group. Most clasts, 

especially Mount Hood andesites in upper parts of exposures, are highly weathered and easily cut by shovel or 

broken by rock hammer, revealing weathering rinds 

several millimeters to 1 cm thick; sand matrix commonly 

leached to light-gray color. Basal contacts where exposed 

are strath surfaces on hyaloclastic sandstone member of 

the Troutdale Formation (Ttfh) at elevations between 300 

and 350 ft (90 and 105 m). Locally capped by loess (Qlo) 

and fine-grained Missoula-flood deposits (Qfs). Distribution and composition of unit indicate deposition during a 

major aggradational episode in the ancestral Sandy River, 

probably in conjunction with glaciation of the Mount 

Hood region; concentrations of Mount Hood andesite 

boulders and gray silty sands may reflect deposition, in 

part by lahars, associated with eruptive activity. Age 

uncertain, but probably much greater than 100 ka judging 

from weathering and geomorphic position. Luminescence 

analysis on sand near the base of the unit in the southern 

part of the map area indicates some of these deposits are 

older than 220 ka. Corresponds in part to the Gresham 

Formation as defined and mapped by Trimble (1963)

Washougal River terrace deposits (Holocene and 

Pleistocene)—Fluvial gravel and sand forming terraces 

in valleys of Washougal and Little Washougal Rivers

Terrace deposits of lower Washougal River (Holocene 

and Pleistocene)—Unconsolidated sandy gravel and sand 

underlying small terraces, with elevations between 50 and 

130 ft (15 and 40 m) along lower Washougal River; generally <10 m thick. Gravel is poorly sorted, locally imbricated, and varies from compact with sand matrix to loose 

openwork texture. Clasts subangular to well rounded, 

derived from Tertiary volcanic and granitic rocks of 

Cascade Range, Columbia River Basalt Group, and Troutdale Formation. Deposits minimally weathered; inferred 

to represent aggradation behind former blockage by 

coarse-grained Missoula-flood bar (Qfg) that now 

constricts mouth of Washougal River

Terrace deposits of upper Washougal River 

(Pleistocene)—Unconsolidated to weakly consolidated 

cobbly gravel and sand forming terraces along Washougal 

River north and northeast of Mount Norway; tread elevations between 190 and 310 ft (60 and 95 m); generally less 

than 5 m thick. Poorly to moderately well sorted and 

imbricated, with matrix of coarse sand. Clasts as large as 

50 cm across, well rounded to subrounded, composed of 

Cascade-derived volcanic and granitic rocks. Age uncertain but absence of weathering rinds indicates late Quaternary age. Found within reach of river flanked by large 

landslide complexes; probably formed during short-lived 

periods of aggradation behind stream-blocking landslides

Terrace deposits of Little Washougal River 

(Pleistocene)—Unconsolidated, little-weathered gravel 

and sand flanking Little Washougal River; as much as 5 m 

thick. Gravel is poorly sorted, composed of subangular to 

well-rounded clasts derived from Tertiary volcanic and 

granitic rocks of Cascade Range, Columbia River Basalt 

Group, and Troutdale Formation. Inferred to record aggradation behind landslides that temporarily blocked river

Cataclysmic-flood deposits (Pleistocene)—Sediment deposited by colossal glacier-outburst floods caused by 

repeated failure of ice dam at Clark Fork that formed 

Pleistocene Lake Missoula in western Montana (Bretz, 

1925, 1959; Bretz and others, 1956; Trimble, 1963; 

Allison, 1978; Baker and Bunker, 1985; Waitt, 1985, 

1994, 1996; Atwater, 1986; O’Connor and Baker, 1992; 

Benito and O’Connor, 2003). Largest floods achieved 

stages of 400 to 500 ft (120 to 150 m) as they spread and 

slowed over the eastern Portland Basin after exiting the 

western Columbia River Gorge with velocities of 35 m/s 

at peak discharge (Benito and O’Connor, 2003). Deposited coarse traction load in series of large bars and plains, 

chiefly west of map area and including Portland delta of 

Bretz (1925). Downstream constrictions temporarily 

ponded floodwater in Portland Basin, promoting deposition (Trimble, 1963). Radiocarbon and tephrochronologic 

data from outside map area indicate depositional ages of 

20 to 15 ka (Waitt, 1985, 1994; Atwater, 1986; Benito 

and O’Connor, 2003; Clague and others, 2003; O’Connor 

and Benito, 2009). Coarse bedload deposits and fine 

slack-water deposits mapped separately

Sand and silt facies—Unconsolidated light-brown to lightgray silt, clay, and fine to medium sand. As much as 20 m 

thick at low elevations in the region but thins toward 

upper mappable extent at 400 ft (120 m) elevation in map 

area. Upper map limit only approximately placed on basis 

of topography owing to difficulty in distinguishing unit 

from similar loess and clayey soils that cover most upland 

surfaces. Poorly exposed, but rare fresh exposures show 

multiple, 0.25- to 1.5-m-thick, fining-upward sequences 

of ripple cross-stratified, very fine sand grading up to 

massive bioturbated clayey silt. Sand composed of quartz, 

feldspar, and conspicuous mica, indicative of a Columbia 

River provenance. Coarser sand facies contain abundant 

dark volcanic rock fragments. Interpreted as slack-water 

sediment settled from temporarily ponded floodwater. 

May locally include compositionally similar loess. Regionally correlative to Trimble’s (1963) Quaternary lacustrine 

deposits (Qlg), but he shows no such deposits in the map 

area

Gravel facies—Unconsolidated, gray, stratified, bouldery to 

cobbly gravel and sand organized into prominent large bar 

along lower reach of Washougal River. Base not exposed, 

but bars reach heights of 20 m above enveloping Columbia 

River floodplain. Well logs west of map area indicated 

total thickness locally as great as 68 m (Hoffstetter, 1984; 

Hartford and McFarland, 1989). Texturally and compositionally variable; most clasts derived from Columbia River 

Basalt Group but also includes blocks of Troutdale Formation and Pliocene–Quaternary Cascadian basalt, all probably entrained in western Columbia River Gorge. Likely 

deposited during multiple flood events between 20 and 15 

ka (Benito and O’Connor, 2003; O’Connor and Benito, 

2009). Finer sand facies probably deposited by late floods 

confined to Columbia River valley. Mostly equivalent to 

Trimble’s (1963) Quaternary lacustrine gravel (Qlg) but 

unit includes local sand accumulations below 200 ft (60 m) 

elevation, in part mapped as sand and silt deposits (Qs) by 

Trimble (1963)

BASIN-FILL DEPOSITS

Unnamed conglomerate (Pleistocene and Pliocene?)-

Unconsolidated to semiconsolidated, deeply weathered, 

pebbly to bouldery conglomerate; overlies lithologically 

similar but older conglomerate member of the Troutdale 

Formation (Ttfc); thick-bedded, poorly sorted to moderately well sorted, clast supported, commonly imbricated 

and crossbedded; includes thin lenses (<2 m thick) of 

basaltic and (rarely) quartzofeldspathic sand. Wellrounded to subrounded clasts as large as 50 cm across 

derived mostly from Columbia River Basalt Group; sparse 

clasts of volcanic rocks eroded from Cascade Range and 

quartzite also present. Typically more poorly sorted and 

has more diverse clast population than underlying Troutdale Formation conglomerate member, but general lithologic similarity of the two units makes contact difficult to 

locate; inferred to be more than 60 m thick where exposed 

in landslide scarps on south side of Little Washougal 

River valley. Clast imbrication indicates transport to 

northwest. Age uncertain but to west of map area overlies 

hyaloclastic sandstone member of Troutdale Formation 

(Ttfh) (Evarts and O’Connor, 2008)

Unnamed fan gravel (Pleistocene and Pliocene?)—Deeply 

weathered unconsolidated sand and cobbly gravel poorly 

exposed along Sandy River valley near southern boundary 

of quadrangle; underlies extensive northwest-sloping 

piedmont surface south of the map area and west of Sandy 

River. Clasts consist chiefly of andesite and other Cascade 

Range rock types; weathering rinds on clasts exceed 1 cm 

thick. Locally includes diamicts, interpreted as lahar and 

lahar-runout deposits, that contain 1-m-diameter clasts of 

pyroxene and hornblende andesite. Capped by as much as 

(25 m) of strongly oxidized and pedogenically altered 

micaceous silt, inferred to be loess (Qlo). Morphology 

and composition of unit indicate deposition in broad fan 

by an ancient Sandy River draining Cascade Range. 

Topographic position, degree of weathering, and thick 

overlying loess mantle imply substantial age, probably 

early Pleistocene. Lahar deposits derived from an ancient 

volcanic center, possibly the Sandy Glacier volcano 

(Wise, 1969; Sherrod and Scott, 1995) located in the 

Mount Hood area. Mapped as Springwater Formation by 

Trimble (1963), but geomorphic relations outside the map 

area indicate that it is probably younger than deposits in 

the type area near Springwater, about 30 km south of map 

area

Troutdale Formation (Pliocene and Miocene?)-Semiconsolidated to well-consolidated conglomerate and sandstone. Divided into two informal members that, in the 

map area, are typically separated by an erosional unconformity

Hyaloclastic sandstone member (Pliocene)—Fluvial 

sedimentary strata distinguished by indurated, coarse sandstone composed of abundant grains of glassy, 

olivine+plagioclase-phyric basalt and conglomerate that 

contains olivine-bearing basalt clasts; well exposed on 

Crown Point Highway and along Sandy River, where it 

overlies and intertongues with micaceous arkosic sandstone, siltstone, and claystone of the Sandy River Mudstone (Tsr). Hyaloclastic sandstone (equivalent to vitric 

sandstone of Trimble (1963) and Tolan and Beeson (1984)) 

consists largely to entirely of angular to subrounded 

fragments, 2 to 6 mm across, of black, generally nonvesicular basalt that contains phenocrysts of olivine (0.5–2 

mm) and plagioclase (1–3 mm) in a glassy (sideromelane) 

to intergranular groundmass; sideromelane partly to completely altered to palagonite, which cements sandstone and 

imparts a distinctive yellowish-brown color to the originally dark green rock; many beds contain minor admixed 

nonvolcanic debris such as quartz, muscovite, hornblende, 

and potassium feldspar. Sandstone ranges from poorly 

sorted to well sorted; typically thick-bedded, commonly 

lenticular, crossbedded, and contains dispersed pebbles 

and cobbles of olivine-bearing basalt. Interbedded 

conglomerate mostly well sorted and clast supported; 

consists of well-rounded to subrounded pebbles and 

cobbles of variably vesicular, olivine+plagioclase-phyric 

basalt, basaltic rocks of Columbia River Basalt Group, and 

generally minor amounts of quartzite and other rock types; 

some conglomerate beds poorly sorted, with subangular 

basalt boulders as large as 1 m across. Angular nonvesicular vitric clasts in hyaloclastic sandstone beds interpreted 

as debris generated by basalt-water interaction in the 

Columbia Gorge that was rapidly transported downstream 

and deposited in eastern Portland Basin (Trimble, 1963; 

Swanson, 1986, 1988). Vitric clasts and associated basalt 

cobbles exhibit a low-potassium-tholeiite composition 

(Swanson, 1986, 1988; Lite, 1992; A.W. Sarna-Wojcicki, 

written commun, 2005), indicating probable derivation 

from compositionally similar middle Pliocene basalt flows 

east of map area (Swanson, 1986, 1988; R.C. Evarts and 

R.M. Conrey, unpub. mapping)

Conglomerate member (Pliocene and (or) Miocene)-

Consolidated, well sorted, clast-supported, pebble and 

cobble conglomerate composed largely of well-rounded 

clasts of Columbia River Basalt Group with minor but 

persistent quartzite and granitic and felsic metamorphic 

rocks; sparse interbeds of volcanic lithic and micaceous 

quartzofeldspathic sandstones; mapped only north of 

Columbia River but some conglomerate mapped as Ttfh 

south of river, especially west of Chanticleer Point, may 

actually belong to this unit. Intensely weathered to depths 

of several meters. Well logs indicate unit is more than 200 

m thick east of Campen Creek. Equivalent in part to upper 

member of Troutdale Formation of Mundorff (1964) and to 

lower member of Troutdale Formation of Tolan and 

Beeson (1984). Late Miocene to early Pliocene age 

inferred from stratigraphic relations outside of quadrangle 

(Trimble, 1963; Tolan and Beeson, 1984)

Sandy River Mudstone (Pliocene and Miocene)-

Semiconsolidated, well-bedded sandstone, siltstone, 

claystone, and minor quartzite-bearing conglomerate, 

pumice-lapilli tuff, and lignite; crops out along Sandy 

River at south edge of map area (Trimble, 1963). Thickness highly variable due to lateral gradations to gravel and 

to erosion; well logs show unit thicknesses less than 65 m 

in Sandy River area (Swanson and others, 1993) but more 

than 150 m thick where buried beneath volcanic rocks and 

landslide debris in northern part of map area; may be 

more than 300 m thick in Camas quadrangle to west 

(Hartford and McFarland, 1989; Swanson and others, 

1993). Sandy and silty beds are bluish gray in fresh exposures, but more typical weathered exposures are light 

brown and commonly limonite-cemented. Consist of 

subangular grains of quartz, feldspar, various rock 

fragments, muscovite, and minor biotite, tourmaline, magnetite, hornblende. Thin claystone beds varicolored, commonly carbonaceous, and locally tuffaceous. Planar and 

trough crossbeds and cut-and-fill structures within sandy 

horizons indicate a fluvial depositional environment. Age 

basalt flows in the Columbia Basin. Nomenclature follows 

Swanson and others (1979) and Beeson and others (1985)

Priest Rapids Member—Uppermost member of the 

Wanapum Basalt (Swanson and others, 1979). In this quadrangle, represented by a single intracanyon flow

Basalt of Rosalia of Beeson and others (1989)—Thick 

flow and associated hyaloclastite of olivine- and 

plagioclase-microphyric basalt; fills paleocanyon cut into 

Frenchman Springs Member, Grande Ronde Basalt, and 

older rocks (Waters, 1973; Tolan, 1982; Tolan and Beeson, 

1984); approx 200 m thick near southwest margin of paleocanyon at Chanticleer Point; more than 220 m thick along 

axis of paleocanyon at Crown Point, just east of map area 

(Tolan, 1982). Lava flow, with thin colonnade and thick, 

hackly jointed entablature, sharply overlies and locally 

invades stratified hyaloclastite, which constitutes 25–60 

percent of total thickness (Tolan, 1982; Tolan and Beeson, 

1984); locally grades laterally into pillow-lava zones, 

which are unrelated to basal hyaloclastite (Waters, 1973; 

Tolan, 1982; Tolan and Beeson, 1984). Hyaloclastite is 

well indurated, poorly sorted, and composed of 

subrounded to well-rounded, sand- to cobble-size clasts of 

brownish-yellow, partially palagonitized sideromelane 

(Tolan, 1982). Local foreset bedding and clast imbrication 

indicate northwest transport direction. Lava flow is 

plagioclase-microphyric and contains rare plagioclase 

crystals to 10 mm long in intergranular to intersertal 

groundmass of plagioclase, olivine, augite, Fe-Ti oxides, 

and minor to abundant interstitial glass; vesicles typically 

filled with yellow clay. Chemistry of flow and hyaloclastite similar, resembling the Rosalia chemical type of Swanson and others (1979); distinguished from other Wanapum 

Basalt flows by higher concentrations of TiO2

 (3.6 wt 

percent), P2O5 (0.8 wt percent), and FeO* (>14.5 wt 

percent). Reversed magnetic polarity (Swanson and others, 

1979; Tolan, 1982; Tolan and Beeson, 1984). Age approximately 14.5 Ma (Tolan and others, 1989)

Frenchman Springs Member—Most voluminous and 

widespread member of Wanapum Basalt (Tolan and 

others, 1989). Three Frenchman Springs flows overlie 

Grande Ronde Basalt near Corbett (Tolan, 1982)

Basalt of Sentinel Gap of Beeson and others (1985)-

Single thin (8 m) flow of hackly jointed, microphyric 

basaltic andesite (52.4 wt percent SiO2

); overlies basalt of 

Sand Hollow on Corbett Hill Road about 0.5 km east of 

Corbett Station; overlain by hyaloclastic sandstone 

member of Troutdale Formation (Tolan, 1982). Contains 

sparse phenocrysts ≤1 mm long of plagioclase, brown 

augite, and olivine in abundant opaque glass. Lithologic 

characteristics, stratigraphic position, chemistry, and 

normal magnetic polarity (Tolan, 1982; J.T, Hagstrum, 

written commun., 2006) indicate this flow is a high-P2O5

variant of the informal basalt of Sentinel Gap of Beeson 

and others (1985, 1989), which is stratigraphically near the 

top of the Frenchman Springs Member

Basalt of Sand Hollow of Beeson and others (1985)-

Blocky to columnar to hackly jointed, sparsely but 

coarsely plagioclase-phyric basaltic andesite (52.3–52.7 

wt percent SiO2); two flows, totaling 40 m thick, overlie 

Grande Ronde Basalt and underlie basalt of Sentinel Gap 

near Corbett Station and on slopes to east; flow exposed in 

quarry at Corbett Station contains local zones of pillow 

lava and hyaloclastic breccia, is approximately 50 m thick, 

and may be an intracanyon flow (Tolan, 1982; Tolan and 

others, 1984). Basalt of Sand Hollow flows, capped by a 

thick paleosol, also crop out in the headwall of the Rooster 

Rock landslide. Distinguished by scattered large (to 3.5 cm 

across) phenocrysts and glomerocrysts of amber plagioclase; groundmass typically microphyric, intersertal to 

intergranular, composed of plagioclase, brown augite, 

Fe-Ti oxide, olivine (partly altered to clay), and red-brown 

interstitial glass; microvesicles typically filled with 

yellow-brown isotropic clay or calcite. Stratigraphic 

position, chemistry, petrography, and normal magnetic 

polarity (Tolan, 1982; J.T. Hagstrum, written commun., 

2008) indicate correlation with informal basalt of Sand 

Hollow of Beeson and others (1985), erupted approximately 15 Ma (Beeson and others, 1985; Barry and others, 

2010)

Grande Ronde Basalt (Miocene)—Light-gray to black flows 

of tholeiitic basaltic andesite; vesicular to microvesicular, 

aphyric to microphyric to very sparsely plagioclasephyric; exhibit relatively low-TiO2

 contents characteristic 

of the Grande Ronde Basalt of the Columbia River Basalt 

Group (Swanson and others, 1979; Mangan and others, 

1986; Beeson and others, 1989; Reidel and others, 1989). 

Flows in this quadrangle generally display blocky to 

columnar jointing patterns and vesicular flow tops; pillow 

lava locally present at base. Typical samples are intergranular to intersertal, with lathlike plagioclase, granular 

clinopyroxene, and Fe-Ti oxide crystals in abundant dark 

glass; some flows contain rare plagioclase phenocrysts to 

15 mm long; textures resemble those described by Long 

and Wood (1986) for correlative flows in the Columbia 

Basin. Based on field, chemical, and paleomagnetic properties, Grande Ronde Basalt flows in map area are 

assigned to the Sentinel Bluffs Member (Reidel and 

others, 1989; Reidel, 2005) within the N2 magnetostratigraphic unit of Swanson and others (1979), which was 

emplaced about 15.5 Ma (Barry and others, 2010)

Sentinel Bluffs Member—Uppermost member of the 

Grande Ronde Basalt (Reidel, 2005; Reidel and Tolan, in 

press). Flows distinguished by relatively high MgO 

contents (4.5–5.0 wt percent MgO) and normal magnetic 

polarity (Reidel and others, 1989; Reidel, 2005). Three 

Sentinel Bluffs flows, totaling at least 50 m thick, crop out 

in cliffs above Interstate 84 between Corbett Station and 

Tunnel Point (Tolan, 1982); both are assigned to the basalt 

of McCoy Canyon of Reidel (2005), which is found near 

the base of the Sentinel Bluffs Member

VOLCANIC AND SEDIMENTARY ROCKS

Tuff (Oligocene)—Olive-green, moderately welded, 

plagioclase-phyric, pumiceous lapilli tuff. Exposure 

beneath landslide debris on shore of Washougal River, 

about 1 km northeast of Mount Norway, is porphyritic, 

composed of euhedral to embayed phenocrysts of plagioclase (approximately 20 percent; about 1–2 mm across; 

locally replaced by albite, calcite, smectite) and small 

grains of pyroxene in zeolitic, originally glassy matrix 

with well-preserved shard texture; about 5–10 percent 

angular lithic clasts, mostly porphyritic volcanic rocks. 

Outcrop in landslide scarp northwest of Mount Norway is 

similar but highly weathered

Volcaniclastic sedimentary rocks (Oligocene)—Thin 

discontinuous lenses of volcaniclastic rocks interbedded 

with and overlying basaltic andesite flows (Tbem) along 

Washougal River. Primarily light-green to dark-brown, 

poorly sorted, lithic lapilli tuff and tuff breccia probably 

deposited by lahars; pervasively altered to smectite, 

kaolinite, and zeolites

Andesite (Oligocene)—Scattered flows of sparsely to abundantly porphyritic to seriate pyroxene andesite. Contain 

phenocrysts of plagioclase (3–20 percent; as long as 3 

mm), clinopyroxene (0.5–1 percent; as large as 2 mm 

across), orthopyroxene (0.3–5.5 percent; to 2 mm long; 

partially replaced by smectite), Fe-Ti oxide (0–1.4 

percent) in pilotaxitic groundmass; small amounts of 

olivine phenocrysts (about 0.5 mm across; altered to 

smectite) present in some flows; interstitial glass generally altered to smectite. In Washington, overlies and 

interbedded with basaltic andesite of Elkhorn Mountain 

(Tbem) and overlain by lapilli tuff (Tt); outcrop of platy 

pyroxene andesite near Onion Rock is only occurrence of 

pre-Grande Ronde Basalt rocks in map area south of 

Columbia River

Olivine Basalt (Oligocene)—Isolated flow of dark-gray, 

coarse-grained, seriate, olivine- and plagioclase-phyric 

basalt exposed on south valley wall of Washougal River 

about 2 km northwest of Mount Norway. Contains 

phenocrysts and glomerocrysts of blocky plagioclase (24 

percent; as large as 7 mm across), olivine (9 percent; 1 to 

2 mm across; slightly altered to smectite), and augite (1–2 

percent; 0.5 to 1 mm across) in a coarse intergranular 

groundmass of plagioclase, augite, and Fe-Ti oxide. 

Exhibits low-potassium tholeiite chemistry

Basaltic andesite of Elkhorn Mountain of Evarts (2006b) 

(Oligocene)—Sequence of lava flows and flow breccia 

composed of dark-gray to brown, porphyritic to seriate to 

aphyric tholeiitic basaltic andesite and basalt; unit locally 

includes minor volcaniclastic rocks too small or poorly 

exposed to map. As thick as 1.3 km in map area. 

Individual flows generally about 5 to 8 m thick and 

exhibit platy to blocky to columnar jointing. Typical 

flows contain phenocrysts and glomerocrysts of weakly 

zoned plagioclase (0–25 percent; 1 to 6 mm, rarely more 

than 10 mm long; variably replaced by zeolites and (or) 

clay) and olivine (<3 percent; 0.5 to 3 mm across; commonly partly resorbed and surrounded by rinds of granular 

pyroxene and (or) magnetite; rarely contain minute chromian spinel inclusions; almost invariably replaced by 

some combination of smectite, hematite, carbonate, 

serpentine, quartz and kaolinite). Some flows also contain 

phenocrysts of augite (<1 percent; 0.5 to 1 mm across) 

and microphenocrysts of Fe-Ti oxide. Groundmass 

consists of plagioclase, augite, Fe-Ti oxide, and minor to 

abundant interstitial glass (largely devitrified or replaced 

by smectite, quartz, or calcite); groundmass textures 

chiefly intergranular to trachytic, less commonly subophitic or microphyric. All flows in unit are tholeiitic, and 

many are exceptionally rich in Fe (FeO* as high as 13 wt. 

percent) and poor in Sr (<300 ppm) compared to mafic 

rocks elsewhere in southern Washington Cascade range 

(du Bray and others, 2006; Evarts, 2006a,b; Evarts and 

O’Connor, 2008; R.C. Evarts, unpub. data). Phillips and 

others (1986) obtained K-Ar age of 27.9±1.9 Ma from 

locality near stratigraphic top of unit just north of map 

area; 40Ar/39Ar ages from unit to west and northwest of 

map area range from 27.1±0.1 Ma to 25.5 ± 0.2 Ma 

(Evarts, 2006a,b; Evarts and O’Connor, 2008)

Contact—Solid where location is accurate; long-dashed where 

approximately located; short-dashed where inferred; 

dotted where concealed

Fault—Long-dashed where approximately located; shortdashed where inferred; dotted where concealed; queried 

where existence or extent uncertain. Ball and bar on 

downthrown side. Arrows show relative horizontal movement

Reverse fault—Dashed where inferred, dotted where 

concealed. Sawteeth on upper plate

Strike and dip of beds

Strike and dip of platy parting in lava flows

Strike and dip of eutaxitic structure in pumiceous tuff

Sample locality for chemical analysis—Showing map 

number in table 1

Sample locality for 40Ar/39Ar age determination—-

Showing age±1-σ error. See table 2

Sample Locality for luminescence age—Showing map letter 

in table 3

Sample locality for radiocarbon age—Showing map number 

in table 4

Cinder cone

poorly known but probably ranges from middle Miocene 

to middle Pliocene; in Mount Norway area, well logs 

indicate unit underlies the conglomerate member of the 

Troutdale Formation (Ttfc) along a sharp, probably 

unconformable, contact, whereas to west of map area, it 

underlies or is interbedded with lower part of hyaloclastic 

sandstone member of Troutdale Formation (Ttfh) (Evarts 

and O’Connor, 2008) inferred to be about 3 to 4 m.y. old; 

plant fossils from localities near top of unit along Sandy 

River just south of quadrangle assigned an early Pliocene 

age (Chaney, 1944; Treasher, 1942; Trimble, 1963; Tolan 

and Beeson, 1984)

VOLCANIC ROCKS OF THE BORING VOLCANIC FIELD

Basaltic andesite of Mount Norway (Pleistocene)-Lightgray, aphyric, pilotaxitic, calc-alkaline basaltic andesite 

(56–57 wt percent SiO2

) underlying area around Mount 

Norway (Trimble, 1963; Allen, 1975; Mundorff, 1964); 

very platy flow with weathered vesicular flowtop well 

exposed in headwall scarp of large landslide complex 

along Washougal River; well logs indicate flow is more 

than 120 m thick north of Nichols Hill. Weathered scoria 

and ash cut by dike exposed in roadcut on north flank of 

Mount Norway, which presumably marks vent; Nichols 

Hill also composed of pyroclastic debris and is probably a 

subsidiary vent. Overlies basaltic andesite of Bear Prairie 

(Qmbp). Chemically characterized by intermediate K2O 

content (about 0.9 wt percent). Normal magnetic polarity 

(J.T. Hagstrum, written commun., 2008); sample from 

roadcut directly northwest of Mount Norway gave an 

40Ar/39Ar plateau age of 693±9 ka

Basaltic andesite of Pepper Mountain (Pleistocene)-

Weathered flow of platy, microvesicular, olivine-phyric to 

microphyric basaltic andesite that caps ridge south of 

Howard Canyon; erupted from vent at Pepper Mountain, 

about 6 km east of map area (R.C. Evarts and R.M. 

Conrey, unpub. mapping); no more than 10 m thick. 

Consists of olivine phenocrysts and microphenocrysts 

(5–8 percent; to 1 mm across, a few as large as 2 mm 

across; commonly altered to clay; chromian spinel inclusions) and traces of plagioclase and clinopyroxene in 

fine-grained trachytic groundmass of plagioclase, clinopyroxene, and Fe-Ti oxide. Calc-alkaline, with Mg# = 

62–67, K2

O = 1.0–1.2 wt percent; relatively high Ba 

(500–650 ppm), Sr (1,040–1,300 ppm), and Ba/Nb 

(50–80). Magnetic polarity unknown; sample collected 5 

km east of map area yielded an 40Ar/39Ar age of 846±6 ka 

(R.C. Evarts, unpub. mapping; R.J. Fleck, written 

commun., 2012)

Basalt of Chamberlain Hill (Pleistocene)—Blocky- to 

columnar-jointed flow(s) of gray, diktytaxitic, tholeiitic 

basalt (49.6–50.5 wt percent SiO2) exposed near Chamberlain Hill, a cinder cone that marks the probable vent 

(Treasher, 1942; Trimble, 1963; Allen, 1975); maximum 

thickness about 60 m. Contains phenocrysts of olivine 

(4–5 percent; 1 to 2 mm across; variably oxidized to 

iddingsite or an oxide phase; inclusions of chromian 

spinel) and plagioclase (2–4 percent; 1–2 mm long) in 

holocrystalline intergranular groundmass of olivine, clinopyroxene, plagioclase, and Fe-Ti oxide; troctolite clots 

common. Reversed magnetic polarity (J.T. Hagstrum, 

written commun., 2006). An 40Ar/39Ar plateau age of 

1,159±14 ka was obtained from sample collected in rock 

pit on Mershon Road

Basaltic andesite of Bear Prairie (Pleistocene)—One or 

more flows of light- to dark-gray, columnar-jointed, 

porphyritic, calc-alkaline basaltic andesite (52.5–53 wt 

percent SiO2) that underlie area west-northwest of Mount 

Norway; thickness in map area between 25 and 50 m (80 

and 160 ft). Erupted from vents marked by cinder cones in 

Larch Mountain quadrangle to north (Trimble, 1963; 

Allen, 1975; Hammond and Korosec, 1983; R.C. Evarts, 

unpub mapping); subsequent incision by Washougal 

River has separated flows in map area from source area. 

Flows contain olivine phenocrysts (about 6 percent; 1 to 2 

mm across; variably oxidized; inclusions of chromian 

spinel) in trachytic groundmass of plagioclase, clinopyroxene, olivine, Fe-Ti oxide, and minor interstitial glass. 

Overlies conglomerate and sandstone mapped as Troutdale Formation; overlain by basaltic andesite of Mount 

Norway. Reversed magnetic polarity (J.T. Hagstrum, 

written commun., 2001); sample collected from upper 

flow in adjacent Larch Mountain quadrangle gave 

40Ar/39Ar plateau age of 1,220±8 ka (R.J. Fleck, written 

commun., 2012)

Basaltic andesite of Broughton Bluff (Pleistocene)—Two 

flows of gray, columnar-jointed, calc-alkaline basaltic 

andesite (52–53 wt percent SiO2) that underlie upland area 

west of Chamberlain Hill, the presumed vent (Treasher, 

1942; Trimble, 1963; Allen, 1975); forms discontinuous 

cliff extending east and southeast of Broughton Bluff; as 

thick as 60 m. Contains phenocrysts of olivine (to 9 

percent; mostly 0.5 to 1 mm but a few as large as 3 mm 

across; inclusions of chromian spinel; locally replaced by 

iddingsite) in a trachytic to subophitic groundmass of 

plagioclase, augite, and Fe-Ti oxide. Reversed magnetic 

polarity (J.T. Hagstrum, written commun., 2003). An 

40Ar/39Ar age of 1,292±19 ka was obtained from a sample 

collected near west edge of the map area, consistent with 

K-Ar age of 1.53±0.39 Ma reported by Conrey and others 

(1996a)

Basalt of Bridal Veil Creek (Pleistocene)—Single basalt 

(50.1–50.4 wt percent SiO2) flow with well-developed 

colonnade and entablature that caps narrow ridge north of 

Howard Canyon; about 30 m thick; flowed into map area 

from east (R.C. Evarts, unpub. mapping). Contains olivine 

phenocrysts (7–8 percent; to 5 mm across; iddingsite 

rims; chromian spinel inclusions) in relatively coarsegrained, holocrystalline, intergranular to trachytic groundmass of plagioclase, olivine, greenish-brown clinopyroxene, and Fe-Ti oxide; most samples contain traces phlogopite in groundmass interstices or in vesicles. Overlies 

hyaloclastic sandstone member of the Troutdale Formation Reversed magnetic polarity (J.T. Hagstrum, written 

commun., 2005); 40Ar/39Ar plateau age is 2,284±16 ka

VOLCANIC ROCKS OF THE THE HIGH CASCADE RANGE

Low-potassium tholeiite (Pliocene)—Medium- to dark-gray, 

coarse-grained basalt (49.2 wt percent SiO2) overlying 

hyaloclastic sandstone member of the Troutdale Formation. Approximately 12-m-thick flow exposed in headwall 

scarp of landslide between Chanticleer Point and Crown 

Point (Williams, 1916; Lowry and Baldwin, 1952; 

Waters, 1973; Tolan and Beeson, 1984); isolated outcrop 

south of Cemetary Hill is erosional remnant of a different 

flow judging from slightly different paleomagnetic orientation (J.T. Hagstrum, written commun., 2005) and is 

probable distal end of poorly exposed flow(s) that underlie ridge south of Howard Canyon. Diktytaxitic, commonly vesicular, with vesicle cylinders/segregation veins; 

intergranular to subophitic textures; composed of plagioclase (0.5–1 mm long; variably altered to kaolinite), 

olivine (0.5–1 mm across; variably altered to iddingsite; 

chromian-spinel inclusions), augite (0.5 mm across), 

Fe-Ti oxide, and interstitial glass. Chemically distinguished by low K2

O (0.1–0.3 wt percent) content. Most 

outcrops moderately to severely weathered. Normal magnetic polarity (J.T. Hagstrum, written commun., 2005). 

K-Ar and 40Ar/39Ar ages between 3.0 and 3.6 Ma were 

obtained from correlative flows to east of map area 

(Conrey and others, 1996b; R.J. Fleck, written commun., 

2011)

BEDROCK

COLUMBIA RIVER BASALT GROUP

Wanapum Basalt (Miocene)—Dark gray to black, variably 

vesicular to microvesicular, aphyric to sparsely phyric 

lava flows of high-TiO2 tholeiitic basalt and basaltic 

andesite; exhibit blocky to columnar or hackly jointing 

patterns and vesicular flow tops; upper few meters locally 

thoroughly weathered to red saprolite or laterite. Textures 

resemble those described by Long and Wood (1986) for 

Twfss

Twfsh

Tgsb

Tt

Tvs

Ta

Qac

Qe

Qa

Qt

Qls

Qh

Qlo

Qtds1

Qtds2

Qtds3

Qtdwl

Qtdwu

Qtdl

Qfs

Qfg

QTc

QTfg

Ttfh

Ttfc

Tsr

Qmmn

Qmpm

Qbch

Qmbb

Qbbv Qbch

Qbch Tlkt

Qmbp

Tob

Twprr

Tbem

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

SCALE 1:24 000

CONTOUR INTERVAL 20 FEET

1 1/2 0 1 MILE MAGNETIC NORTH

TRUE NORTH

15.5°

APPROXIMATE MEAN

DECLINATION, 2013

OREGON

WASHINGTON

MAP LOCATION

558000mE

Geology mapped by T.L. Tolan, 1980–1981; 

R.C. Evarts, 1999, 2002-2011; and J.E. 

O'Connor, 2003-2007; assisted by P.A. 

Dinterman, 2002 

GIS database and digital cartography by 

Karen L. Wheeler and Michael.G. Sawlan

Edited by J. L. Zigler 

Manuscript approved for publication 

April 26, 2013 

Base from U.S. Geological Survey, Washougal, WA-OR, 1994

North American Datum of 1927 (NAD27). Projection: 

Washington Coordinate System, south zone (Lambert conformal conic)

10 000-foot ticks: Washington Coordinate System, south zone and Oregon 

Coordinate Systen, north zone

Blue 1000-meter Universal Transverse Mercator ticks, zone 10

Oligocene

QUATERNARY

TERTIARY

BEDROCK

Unconformity

BASIN-FILL DEPOSITS

Qmmn

Qbch

Qbbv

Qmbp

Qmbb

af

0

27.0 

0.015

0.0002

1.0

2.0

3.0

15.5

15.3

14.5

Tob

Tt

Tvs

Tbem

1,159±14 ka

1,292±19 ka

2,284±16 ka

683±9 ka

CORRELATION OF MAP UNITS

Pliocene

and (or)

Miocene

Unconformity

Unconformity

Twfss

Twfsh

Tgsb

Miocene

Columbia River Basalt Group

Qtds2

Qtdwu

QTc

Volcanic and sedimentary rocks

SURFICIAL DEPOSITS

Qe

Holocene

Qtdl

Pleistocene

Tsr

Ttfc

Ttfh

?

?

?

? ?

?

Ta

Qtds3

QTfg

Pliocene

Qh

Qlo

Qls

Qfs

Qac

Qa

Qfg

Qt Qtds1 Qtdwl

Cataclysmic-flood desposits

Local unconformity

?

VOLCANIC ROCKS OF THE

BORING VOLCANIC FIELD

Qmpm

Tlkt

?

?

Sandy River

terrace deposits

Washougal River

terrace deposits

Twprr

Approximate

age in Ma

[Age of epoch boundaries from time scale of Ogg and others (2008). 40Ar/39Ar ages shown are from table 2]

VOLCANIC ROCKS OF

HIGH CASCADE RANGE

1,000

500

FEET

1,500

1,000

500

SEA LEVEL

1,500

SEA LEVEL

500 500

A A'

VERTICAL EXAGGERATION X 2

Thickness of surficial units exaggerated

1,000 feet = 305 meters

Relative movement - , toward viewer; , away from viewer

Tbem

QTc

Tbem

Qtdwl

QTc

Qmmn Qt

Qls

Qa Qls Qtdwu

Mount Norway

WASHOUGAL RIVER

WASHOUGAL RIVER

Ttfc Tsr

Tbem

Tbem

SECTION

C-C'

B B'

1,000

500

FEET

1,500

SEA LEVEL

500

VERTICAL EXAGGERATION X 2

1,000

500

SEA LEVEL

1,500

500

Thickness of surficial units exaggerated

1,000 feet = 305 meters

Relative movement - , toward viewer; , away from viewer

Qh Qls

Qmbb

Qbch Qlo Qlo

Qls

Qls

Ttfh Ttfh

Ta Ta

Ttfh

Ttfh Twfsh

Ttfh

Ttfh

Ttfh

Tgsb

Twfsh

Twfsh

Twfsh

SANDY RIVER

Chamberlain Hill Chanticleer Point

SECTION

C-C'

Tgsb

Qlo Qlo Qlo Qlo

Qtds3

Qlo

Twfss

Twprr

Tgsb

Qlo

C C'

Artificial fill (unit af) too thin to portray on cross section

1,000

500

FEET

1,500

1,000

500

SEA LEVEL

1,500

SEA LEVEL

500 500

VERTICAL EXAGGERATION X 2

Thickness of surficial units exaggerated

1,000 feet = 305 meters

Relative movement - , toward viewer; , away from viewer

Nichols Hill

WASHOUGAL RIVER

SANDY RIVER

Qh

Qfs

Qfs Qtds2

Qtds3

Ttfh

Qac Qfg Ttfc Tbem

QTc Qmmn Qt

Qls

Qls

Tsr

Ttfc Qa

Qac

Qac

Qh

Qls

Qbch

Ttfh

Tbem?

Chamberlain Hill

Reed Island COLUMBIA RIVER OREGON WASHINGTON

Gibbons Creek

SECTION

B-B'

SECTION

A-A'

QTfg

Qbch Qmbb Qbch

A