Origin, Extent, and Thickness of 

Quaternary Geologic Units in the 

Willamette Valley, Oregon

Professional Paper 1620

Prepared in cooperation with Oregon Water Resources Department

U.S. Department of the Interior

U.S. Geological Survey
Cover photographs

 Front cover: Late Quaternary fluvial gravel about 20 meters below the ground surface, at the Delta Sand and Gravel Quarry, near 

Eugene, Oregon. (Photograph by Terrence D. Conlon, U.S. Geological Survey.) 

Back cover: Sequence of Pleistocene deposits exposed along the Willamette River near Monmouth, Oregon. 

(Photograph by Jim E. O’connor, U.S. Geological Survey.)
Origin, Extent, and Thickness of Quaternary 

Geologic Units in the Willamette Valley, Oregon

By JIM E. O’CONNOR, ANDREI SARNA-WOJCICKI, 

KARL C. WOZNIAK, DANIAL J. POLETTE, AND

ROBERT J. FLECK

Prepared in cooperation with 

Oregon Water Resources Department

U.S. Geological Survey Professional Paper 1620
For sale by the

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

Library of Congress Cataloging in Publication Data

author.

 report title 1992 / by .

 p. cm.— (United States Geological Survey professional paper; 1620)

 "Prepared in cooperation with Oregon Water Resources Department."

 s.

 1. 

CIP

 ISBN 

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

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.

Reston, Virginia 2001 

For sale by the

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

Library of Congress Cataloging in Publication Data

Origin, extent, and thickness of Quaternary geologic units in the Willamette Valley, 

Oregon / by Jim E. O'Connor ... [et al.]. ; prepared in cooperation with Oregon Water

 Resources Department.

 p. cm. -- (U.S. Geological Survey professional paper; 1620)

 Includes bibliographical references.

 ISBN 0-607-94832-9

 1. Geology, Stratigraphic--Quaternary. 2. Geology--Oregon--Willamette River Valley.

 I. O'Connor, Jim E., 1959- II. Oregon. Water Resources Dept. III. Series.

QE696 .075 2001

 551.7'9'097953--dc21 00-044293
Contents III

CONTENTS

Abstract .................................................................................................................................................................................... 1

Introduction.............................................................................................................................................................................. 2

Geographic and Geologic Setting ............................................................................................................................................ 2

Quaternary Deposits in the Willamette Valley ........................................................................................................................ 3

Willamette Valley Quaternary Units ................................................................................................................................ 6

Weathered Terrace Gravels ....................................................................................................................................... 6

Pleistocene Sand and Gravel of the Willamette River and Major Cascade Range Tributaries................................. 9

Missoula Flood Deposits ......................................................................................................................................... 20

Holocene Floodplain Deposits of the Willamette River and Major Tributaries...................................................... 26

Other Quaternary Map Units ................................................................................................................................... 29

Thickness and Extent of Quaternary Deposits....................................................................................................................... 30

Methods .......................................................................................................................................................................... 30

Results............................................................................................................................................................................. 32

Thickness of Sand and Gravel Facies of Holocene Floodplain Deposits................................................................ 32

Thickness of Pleistocene Sand and Gravel that Postdates the Missoula Floods..................................................... 32

Summary and Conclusions..................................................................................................................................................... 35

References.............................................................................................................................................................................. 37

Appendix 1—40Ar/39Ar Analyses of Volcanic Materials ..................................................................................................... 43

Appendix 2—Analytical Methods and Results for Tephra Analysis..................................................................................... 46

Appendix 3—14C Age Analyses............................................................................................................................................ 51

PLATE

1. Geologic Map of Quaternary Units in the Willamette Valley, Oregon

FIGURES

1. Correlation chart showing history of stratigraphic frameworks developed for the Willamette Valley, 

including formal and informal nomenclature, assigned ages, and inferred deposit genesis ...................................... 4

2. Correlation chart showing relations between Quaternary geologic units identified in this study and

those identified in the Regional Aquifer System Analysis by Gannett and Caldwell (1998) .................................... 6

3. Generalized geologic sections showing relations of Quaternary geologic units in the study area ............................ 7

4. Profile of Willamette and Middle Fork Willamette Rivers showing positions of surfaces of weathered

terrace gravels and subsurface bedrock beneath the Holocene floodplain................................................................. 8

5. Profile of Willamette and Middle Fork Willamette Rivers showing tops of Pleistocene sand and

gravel deposits and the base of the latest Pleistocene (about 12 ka) deposits.......................................................... 11

6. Generalized stratigraphic diagrams and chronologic information for sections of late Quaternary stratigraphy 

exposed in deep gravel pits in the Willamette Valley .............................................................................................. 12

7. Photograph of Pleistocene sand and gravel exposed at Walling Sand and Gravel pit near Turner Gap ................. 14

8. Photograph of lahar deposit from Mount Jefferson ................................................................................................. 14

9. Photograph and geologic interpretation of Pleistocene deposits exposed on the east bank of the 

Willamette River at river mile 102.5 near Sidney.................................................................................................... 16

10. Correlation of stratigraphic sections measured from exposures along the Willamette River showing locations

of tephra and radiocarbon samples, and the nature of contact between the main body of Missoula Flood 

deposits and the Pleistocene sand and gravel that predates the Missoula Flood deposits........................................ 17

11. Profile of Willamette River showing altitudes and thickness of fine-grained Missoula Flood deposits ................. 21

12. Profile of Willamette and Middle Fork Willamette Rivers showing positions of Holocene floodplain surfaces,

the base of Holocene deposits, and bedrock beneath Holocene deposits................................................................. 27

13. Photograph, schematic representation of a measured stratigraphic section, and Holocene fluvial deposits

exposed along the Willamette River at the southern end of Bear Island (river mile 140) ....................................... 28

14. Approximate thickness of the sand and gravel (channel) facies of Holocene floodplain deposits 

of the Willamette River and major tributaries.......................................................................................................... 33

15. Approximate thickness of the Pleistocene sand and gravel that postdates the Missoula Floods.............................. 34
IV Contents

CONVERSION FACTORS, VERTICAL DATUM

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD

 of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both the

United States and Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

centimeter (cm) 0.3937 inch

millimeter (mm) 0.03937 inch

meter (m) 3.281 foot

kilometer (km) 0.6214 mile

meter (m) 1.094 yard

square kilometer (km2

) 247.1 acre
Abstract 1

Origin, Extent, and Thickness of Quaternary 

Geologic Units in the Willamette Valley, Oregon

By Jim E. O’Connor, Andrei Sarna-Wojcicki, Karl C. Wozniak, Danial J. Polette, and

Robert J. Fleck

Abstract

Stratigraphic and chronologic information 

collected for Quaternary deposits in the Willamette Valley, Oregon, provides a revised stratigraphic framework that serves as a basis for a 

1:250,000-scale map, as well as for thickness estimates of widespread Quaternary geologic units. 

We have mapped 11 separate Quaternary units 

that are differentiated on the basis of stratigraphic, 

topographic, pedogenic, and hydrogeologic properties. In summation, these units reflect four distinct episodes in the Quaternary geologic 

development of the Willamette Valley:

1. Fluvial sands and gravels that underlie terraces flanking lowland margins and tributary valleys were probably deposited 

between 2.5 and 0.5 million years ago. 

They are the oldest widespread surficial 

Quaternary deposits in the valley. Their 

present positions and preservation are 

undoubtedly due to postdepositional tectonic deformation—either by direct tectonic uplift of valley margins, or by 

regional tectonic controls on local base 

level. 

2. Tertiary and Quaternary excavation or tectonic lowering of the Willamette Valley 

accommodated as much as 500 m (meters) 

of lacustrine and fluvial fill. Beneath the 

lowland floor, much of the upper 10 to 50 

m of fill is Quaternary sand and gravel 

deposited by braided channel systems in 

subhorizontal sheets 2 to 10 m thick. 

These deposits grade to gravel fans 40 to 

100 m thick where major Cascade Range 

rivers enter the valley and are traced farther upstream as much thinner valley 

trains of coarse gravel. The sand and 

gravel deposits have ages that range from 

greater than 420,000 to about 12,000 years 

old. A widely distributed layer of sand and 

gravel deposited at about 12 ka (kiloannum, thousands of years before the 

present) is looser and probably more permeable than older sand and gravel. Stratigraphic exposures and drillers’ logs 

indicate that this late Pleistocene unit is 

mostly between 5 and 20 m thick where it 

has not been subsequently eroded by the 

Willamette River and its major tributaries.

3. Between 15,000 and 12,700 years ago, 

dozens of floods from Glacial Lake Missoula flowed up the Willamette Valley 

from the Columbia River, depositing up 

to 35 m of gravel, sand, silt, and clay. 

4. Subsequent to 12,000 years ago, Willamette River sediment and flow regimes 

changed significantly: the Pleistocene 

braided river systems that had formed 

vast plains of sand and gravel evolved 

to incised and meandering rivers that are 

constructing today’s fine-grained floodplains and gravelly channel deposits. Sub-
2 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

surface channel facies of this unit are 

loose and unconsolidated and are highly 

permeable zones of substantial groundwater flow that is likely to be well connected to surface flow in the Willamette 

River and major tributaries. Stratigraphic 

exposures and drillers’ logs indicate that 

this unit is mostly between 5 and 15 m 

thick.

INTRODUCTION

Sedimentary units of Quaternary age are widely 

distributed throughout the Willamette Valley of western Oregon. These deposits host the soils that support 

much of the region's agricultural production; are 

important ground-water sources for domestic, agricultural, and municipal uses; and serve as building sites 

and construction materials for the rapidly growing 

communities of Eugene, Springfield, Corvallis, 

Albany, Salem, Newberg, and Wilsonville. These sediments also record varied Quaternary depositional environments and events resulting from a variety of 

tectonic, volcanic, and climatic influences. Understanding the origin, nature, distribution, and thickness 

of surficial geologic units provides glimpses of past 

geologic environments as well as information that 

can guide future development and resource use in 

the Willamette Valley. The study area (pl. 1) includes 

the large basins of the northern and southern Willamette Valley between Oregon City and Eugene, and 

parts of valleys of the major Cascade Range tributaries. In total, the mapped area is about 5,000 km2 

(square kilometers). 

The purpose of this mapping was to define the 

extent and thickness of major deposits of Quaternary 

age to support numerical modeling of the regional 

ground-water system within the Willamette River 

Basin. This work was funded cooperatively by the 

U.S. Geological Survey (USGS) and Oregon Water 

Resources Department as part of the Willamette 

Ground-Water Study.

Fieldwork was conducted during 1996–97 and 

was primarily directed towards defining a regional 

framework of Quaternary deposits. This framework 

was developed from widely scattered exposures in 

conjunction with radiometric age dating and tephrochronology. A regionally consistent geologic map of 

Quaternary deposits was produced by using this stratigraphic framework to interpret existing topographic, 

geologic, and National Resource Conservation Service 

(NRCS, formerly Soil Conservation Service) soils 

maps. Supplemental information on unit thicknesses, 

subsurface extent, and general facies relationships was 

obtained from inspection of more than 800 drillers’ 

logs for water wells, oil-test wells, and geotechnical 

borings from the collection of State of Oregon Water 

Well Reports maintained in the USGS Oregon District 

office in Portland, Oregon. Many of these wells are 

included in the Willamette Ground-Water Study database of field-located wells (Orzol and others, 2000).

Our understanding of the Quaternary geology of 

the Willamette Valley was aided by discussions with 

Marshall Gannett, Rodney Caldwell, Terrence Conlon, 

Leonard Orzol, William McFarland, David Morgan, 

William Scott, Richard Waitt, Ray Wells, Silvio Pezzopane (all U.S. Geological Survey); John Beaulieu, 

Tom Wiley, Ian Madin (Oregon Department of Geology and Mineral Industries); Patricia McDowell (University of Oregon); Peter Clark (Oregon State 

University; Frank Reckendorf (consultant); Scott 

Burns, Marvin Beeson, and Terry Tolan (Portland 

State University). Tana L. Haluska (U.S. Geological 

Survey) helped construct the thickness maps. The map 

and report were reviewed by Terrence Conlon, William Scott, William McFarland, Marshall Gannett, Ian 

Madin, and John Beaulieu.

GEOGRAPHIC AND GEOLOGIC SETTING

The Willamette Valley is a broad alluvial plain in 

northwestern Oregon flanked on the west by early Tertiary marine sedimentary and volcanic rocks of the 

Coast Range, and on the east by Tertiary and Quaternary volcanic and volcaniclastic rocks of the Cascade 

Range. Tributaries that drain these ranges join the

Willamette River along its 300 km (kilometer) northward course from its inception at the confluence of the 

Coast and Middle Forks near Eugene, to north of Portland where the Willamette River enters the Columbia 

River. Within the map area, the Willamette River 

meanders through an extensive lowland (terrain of low 

relief typically below altitudes of 100–150 m above 

sea level) that is typically 30 to 50 km wide, but is 

locally much narrower where the river has cut gaps 

through transverse uplands (foothills and portions of
Quaternary Deposits in the Willamette Valley 3

the Cascade and Coast Ranges with altitudes greater 

than 100–150 m). Outside of the main Willamette Valley, the valley floors of the major Coast Range and 

Cascade Range tributaries are typically less than 3 km 

wide. 

The Willamette Valley has been a topographic low 

for at least 15 million years. The distribution and 

thickness of middle Miocene flood basalts of the 

Columbia River Basalt Group (CRBG) indicate that 

by about 15 Ma1 (mega-annum; millions of years 

before present), a broad lowland existed in the present 

location of the northern Willamette Valley (Gannett 

and Caldwell, 1998). Subsequent uplift of the Coast 

and Cascade Ranges has further defined the basin of 

the Willamette Valley along the north-south axis of a 

regional synclinorium and has resulted in continued 

filling of the lowlands with sediment from the flanking 

mountain ranges (Yeats and others, 1996). Structural 

deformation, including subbasin subsidence and faulting, has created uplands of Columbia River Basalt 

Group rocks across this synclinorium between Albany 

and Salem that separate the northern Willamette Valley from the southern Willamette Valley, as well as 

bounding the Stayton subbasin southeast of Salem 

(Crenna and others, 1994). Faulting and PliocenePleistocene basalt flows form uplands near Oregon 

City that separate the Portland Basin from the northern 

Willamette Valley (Beeson and others, 1989; Madin, 

1990, 1994). Sherrod and Pickthorn (1989) suggested 

that the southern Willamette Valley is primarily a 

strike valley formed by preferential excavation of 

softer geologic units, whereas the northern Willamette 

Valley and Stayton subbasin are primarily tectonic 

depressions (Yeats and others, 1996). Gannett and 

Caldwell (1998) and Yeats and others (1996) provide 

more detailed summaries of the pre-Quaternary geologic history and structural evolution of the Willamette Valley and the flanking mountain ranges.

The basins of the Willamette Valley and tributary 

valleys have accumulated up to 500 m of Neogene and 

Quaternary fill from the surrounding uplands and the 

Columbia River Basin. This alluvial fill contains the 

vast majority of the ground water used in the Willamette Valley. The valley and basin sediments range 

from fine-grained Miocene(?) and Pliocene fluviallacustrine deposits near the basin bottoms to Quaternary-age sediment in the upper 0 to 100 m that are primarily coarse-grained fluvial deposits derived from 

the Cascade Range and Missoula Flood sediment from 

the Columbia River Basin (Gannett and Caldwell, 

1998). This report focuses on the extent, chronology, 

and thickness of the near-surface deposits that are 

mostly of Quaternary age.

QUATERNARY DEPOSITS IN THE 

WILLAMETTE VALLEY

For more than 100 years, geologists, geomorphologists, and soil scientists have investigated late Tertiary and Quaternary deposits in the Willamette Valley.

These efforts resulted in a variety of local and regional 

maps of landforms (Balster and Parsons, 1968), surficial geology (for example, Piper, 1942; Allison, 1953; 

Allison and Felts, 1956; Glenn, 1965; Beaulieu and 

others, 1974; Bela, 1979, 1981; Gannett and Caldwell, 

1998), and soils (Williams, 1972; Otte and others, 

1974; Knezevich, 1975, 1982; Gerig, 1985; Langridge, 1987; Patching, 1987). This work, as well as 

more local stratigraphic studies (for example, Balster 

and Parsons, 1969; Roberts, 1984), have led to a variety of conceptual models of the chronology, stratigraphic relations, and depositional environments

of Quaternary deposits within the Willamette Valley 

(fig. 1). Glenn (1965, p. 11–28), and more recently 

McDowell (1991), thoroughly summarized much of 

this work in addition to pointing out many stratigraphic and chronologic problems and inconsistencies 

with then-current models of the Quaternary geology of 

the Willamette Valley. Many of these problems can be 

ascribed to two factors: (1) the paucity of chronologic 

control and (2) misapplication of broad conceptual 

models of landscape development and Quaternary 

stratigraphy. The latter factor was especially important 

in development of hypotheses regarding the stratigraphic relations, chronology, and genesis of deposits 

left by the Missoula Floods.

For this study, the stratigraphic framework of Quaternary deposits was updated by (1) direct examination 

of field exposures, (2) new chronologic information, 

and (3) incorporating results of recent studies of Quaternary geology elsewhere in the Pacific Northwest. 

Deep gravel pits and riverbanks provide many exposures of Quaternary stratigraphy throughout the Willamette Valley. Tephra correlations and radiometric 

dating of organic and volcanic materials contained in 

many exposures substantially increase chronologic

1“Ma” refers to millions of years before present, and in this 

report is used to indicate radiometric and fission track ages on volcanic rocks.
4 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Figure 1. History of stratigraphic frameworks developed for the Willamette Valley, including formal and informal

units. Reckendorf [1993] provided an alternative interpretation of ages and formative processes for the stratigraphic

Piper (1942) Allison (1936, 1953, 1978) Glenn (1965) 

Unit Genesis Unit Genesis Age Unit Genesis Age 

Quaternary

Holocene 

Younger 

alluvium 

Floodplains of 

present 

streams 

Recent 

alluvium 

Modern 

floodplain 

deposits 

Younger 

than 

11,000±230 

yr BP 

Pleistocene 

Older 

Alluvium 

Willamette Silt 

“Second 

Bottom” 

Deposits 

Climactic 

Missoula 

Flood 

Late 

Pleistocene 

Erratics in "grey 

pebbly silts" 

Climactic 

Missoula 

Flood 

Ice-rafted 

Erratics 

Main 

Valley 

Silts 

Multiple 

Missoula 

floods into 

Willamette 

Lake 

Late 

Pleistocene 

River Bend 

Unit III; 

Columbia River 

provenance 

rhythmically 

bedded silt, clay, 

and sand 

More than 

40 

Missoula 

floods into 

Willamette 

Lake 

Older than 

19 ka 

River Bend Unit II; 

Willamette Basin 

provenance sand 

and silt 

Willamette 

Basin 

fluvial 

deposits 

Linn Gravel 

“Eroded 

phase of 

Linn 

Gravels” 

Glaciofluvial 

deposition 

Early 

Wisconsin 

or Illinoisan 

River Bend 

Unit I; 

Willamette 

provenance 

Basin sand 

and silt 

Mill 

CreekSalem 

Gravels 

Fluvial 

gravels 

Older than 

37,000 yr BP 

(Troutdale 

equivalent?) 

Deposition 

began prior to 

34,410 

± 3,450 yr BP, 

older than 

19 ka Linn 

Gravel 

Terrace 

Deposits 

Lefler Gravel 

Glaciofluvial 

deposition 

Kansan High Molalla 

Gravels 

Glaciofluvial 

deposition 

Lacomb Gravel 

Glaciofluvial 

deposition 

PreKansan 

Tertiary 
Quaternary Deposits in the Willamette Valley 5

nomenclature, assigned ages, and inferred deposit genesis. (Colors indicate correlations between individual stratigraphic

framework developed by Balster and Parsons [1968, 1969].)

Unit Genesis Age Unit Genesis Age 

Recent alluvium Silt and 

clay of 

minor 

tributaries 

(Qalf) 

Holocene 

floodplains 

of the 

Willamette 

River and 

major 

tributaries 

(Qalc) 

Cut and 

fill 

deposits 

of modern 

streams 

and rivers 

Younger 

than 13 ka 

Floodplain 

deposits of 

meandering 

and 

anastomosing 

channels 

Younger than 

11,000±230 yr BP 

and 12,170±70 

yr BP; locally 

younger than 

7 ka; but 

probably mostly 

less than 4 Ka 

Roberts (1984) This Study 

Willamette Formation 

Greenback 

Member 

Climactic 

Missoula 

Flood 

Latest 

Pleistocene 

sand and gravel 

of Willamette 

River and 

major Cascade 

Range 

tributaries 

(Qg1) 

Structureless 

silt, clay, minor 

sand on top of 

rhythmically 

bedded silt 

(not a map unit) 

Aggradation 

by braided 

stream 

systems 

About 

12,170±70 yr BP 

near Turner 

Gap; probably 

everywhere 

younger than 

13,080±300 yr BP; 

older than 7 ka 

Irish Bend 

Member 

Estuarine 

deposits 

within 

“Willamette 

Sound” 

Early phase 

Missoula flooding 

(60-50 ka) 

Irish 

Bend, 

River 

Bend 

Members 

Older than 

13,080±300, 

younger 

than 

28,480±1,810 

yr BP 

Missoula Flood Deposits 

Columbia 

River 

provenance 

clay, silt 

(Qff1) 

Late, smaller 

Missoula 

Floods; may 

locally include 

early 

Holocene 

Willamette 

River deposits 

Older than 

12,2403±330 yr BP, 

probably mostly 

13.5 to 12.7 ka; 

perhaps 

younger than 

13,080±300 yr BP 

Columbia River 

provenance 

clay, silt, sand, 

and local gravel 

(Qff2, Qfc) 

Multiple 

Missoula 

Floods 

Older than 

12,240±330 yr BP, 

younger than 

22,060±100 yr BP; 

about 

15 to 13.5 ka 

Wyatt Member Willamette 

Basin fluvial 

deposits 

Rowland Formation

Diamond Hill 

Member 

Linn Member Willamette River 

fluvial deposition 

Dolph Surface 

High Terrace 

Gravels 

Eola Surface 

Fluvial 

deposition, 

pedimentation, 

and 

pedogenesis 

Monroe 

Clay 

Genesis Age 

Horseshoe 

Surface 

Balster and Parsons (1968, 1969) 

Low 

floodplains 

Youngest 

floodplains 

Unit 

Historic 

(less than 

150 yr) 

Dominant 

“current” 

floodplains 

Between 

3,290±120 

and 

555±110 yr 

BP 

Higher 

floodplains 

Ingram Surface 

Winkle 

Surface 

Coarse 

facies 

Fine 

facies 

Late phase 

Missoula flooding, 

(15-12 ka) 

Greenback 

Member 

Willamette Formation (Senecal, Calapooyia Surfaces)

Mixture of local fluvial 

deposits, Bonneville 

Flood deposits, and 

Missoula Flood 

deposits 

Estuarine 

deposits 

within 

"Willamette 

Sound” 

Malpass 

Member 

Late 

Miocene or 

Pliocene 

From older than 

about 420 ka in 

Eugene area 

(older than 

75-100 ka near 

Salem), to 

younger than 

23.2 ka. 

Older than 22 ka 

Aggradation 

by braided 

stream 

systems 

Pleistocene 

sand and gravel 

of Willamette 

River and major 

Cascade Range 

tributaries 

(Qg2) 

Deposition 

began prior to 

36,000 ±3,000 

yr BP and 

continued to 

at least 

28,480±1,810 

yr BP 

Willamette Basin 

provenance sand 

and silt in northern 

Willamette Valley 

(not a map unit) 

Willamette 

Basin fluvial 

deposits, or 

first Missoula 

Floods 

Older than 

about 15 ka; 

younger 

than 22 ka 

Linn Formation 

Variable; 

perhaps locally 

older 

than 12 ka to 

younger than 

5,860±120 yr BP 

Bioturbated 

loess, 

colluvium, 

overbank, 

and local 

drainage 

deposits 

Lacustrine 

Sandur 

(outwash) 

deposits 

Linn 

Gravels 

Diamond 

Hill 

Member 

Multiple 

Missoula 

Floods into 

Willamette 

Lake 

Older than 

13,080 ±300, 

younger than 

28,480 ±1,810 

yr BP 

Fine facies; 

natural high 

flood plains 

prior to 

regulation 

Coarse 

facies; 

reworked 

Linn 

Gravel 

From 

12,240±330 

to 

5,250±270 

yr BP 

Braided river 

deposits; high 

floodplains of 

modern rivers 

Pedimentation, 

gravel 

deposition 

Pedimentation, 

gravel 

deposition 

"Beyond 

radiocarbon 

dating" 

Early 

Pleistocene 

Middle 

Pleistocene 

Low-energy 

Willamette River 

fluvial deposits; 

soil formation 

Older than 

420 ka, younger 

than 

about 4.5 Ma in 

Santiam 

drainage, 

younger than 

about 800 ka 

near Eugene, 

probably mostly 

2.5 to 0.5 Ma 

Weathered 

Terrace Gravels 

(QTg, QTt) 

Reckendorf 

(1993) 
6 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

information for these deposits. These stratigraphic and 

chronologic relations, aided by consideration of 

deposit characteristics, surface morphology, and current understanding of regional Quaternary environments, lead to the stratigraphic framework proposed in 

this report. This framework is general and is based on 

reconnaissance-level correlations, thus it is sure to be 

modified as more detailed studies are conducted and 

regional understanding of Quaternary events evolves. 

Nevertheless, this stratigraphic framework provides a 

regionally consistent basis for mapping the surficial 

geology shown on plate 1 and for estimating thicknesses of hydrogeologically significant Quaternary 

units. The relation of Quaternary stratigraphic units 

identified in this report to those of previous studies is 

shown in figure 1; the relation to the hydrogeologic 

units defined by Gannett and Caldwell (1998) is

shown in figure 2.

Many Quaternary stratigraphic units in the Willamette Valley have been assigned a variety of formal 

and informal lithostratigraphic names by past workers 

(fig. 1), now making it difficult to use formal stratigraphic names on a regional basis. Consequently, we 

have generally not used such names in favor of 

descriptive unit names. Nevertheless, formal and 

informal names are referred to in the following unit 

descriptions to aid comparison with previous studies 

and nomenclature.

Willamette Valley Quaternary Units

Weathered Terrace Gravels (QTg)

Weathered fluvial gravels and associated pediment 

surfaces locally flank the main valley floors. The main 

localities are where they underlie a series of broad 

piedmonts along the eastern margin of the northern 

Willamette Valley between Molalla and Silverton, low 

terraces along the western margin of the southern 

Willamette Valley between Corvallis and Eugene, 

scattered terrace remnants on uplands that cross the 

main axis of the valley, and high terraces and fan remnants above the valley floor along most of the major 

Cascade Range tributaries (fig. 3). They wholly or 

partly include the terrace deposits of Piper (1942), the 

Leffler and Lacomb gravels of Allison (1936, 1953), 

the decomposed sediment of Baldwin and others 

(1955), the Quaternary higher terrace deposits of Bela 

(1979), and the upper and middle terraces of Beaulieu 

and others (1974). Where similar deposits have been 

mapped as Troutdale Formation near Molalla (Trimble, 1963; Hampton, 1972), we have retained that 

designation (mapped as unit QTt), although there 

is no clear distinction between deposits mapped as 

Troutdale Formation and the weathered terrace gravels 

that underlie piedmont surfaces to the immediate 

southwest. The Quad, Dolph, and Eola geomorphic 

surfaces of Balster and Parsons (1968) partly correspond to the distribution of weathered terrace gravels 

and nearby pediments.

This Study Willamette RASA Study

Surficial Geological Unit Geologic Unit

Holocene Pleistocene

Tertiary Quaternary

Holocene 

floodplain 

deposits of 

the Willamette 

River and 

major 

Cascade 

Range 

tributaries 

(Qalc)

Silt and clay 

of minor 

tributaries 

(Qalf)

Missoula 

Flood 

deposits of 

clay, silt, and 

minor sand 

(Qff2)

Willamette 

Silt (finegrained 

Missoula 

Flood 

deposits)

Coarsegrained 

Missoula 

Flood 

Missoula deposits Flood 

deposits of 

sand and 

gravel (Qfc)

Holocene 

alluvial 

deposits

Missoula Flood(?) deposits of 

clay, silt, and minor sand 

Pleistocene (post-MissoulaFlood) sand and gravel of 

the Willamette River and 

major Cascade Range 

tributaries (Qg1)

Pleistocene (post-MissoulaFlood) sand and gravel of 

the Willamette River and 

major Cascade Range 

tributaries (Qg2)

Coarse-grained 

basin-fill sediment

Weathered 

Terrace 

Gravels (QTg)

Troutdale 

Formation 

(QTt)

Terrace 

deposits

Troutdale 

Formation

Figure 2. Relations between Quaternary geologic 

units identified in this study and those identified in

the Regional Aquifer System Analysis (RASA) by 

Gannett and Caldwell (1998). (Shaded areas indicate

units that are components of the Willamette Aquifer

hydrogeologic unit of Gannett and Caldwell [1998]

within the Willamette lowland.)
Quaternary Deposits in the Willamette Valley 7

0

0 5000 FEET

500 1000 1500 METERS

VERTICAL EXAGGERATION X 50

DATUM IS SEA LEVEL

60

50

40

30

20

10

90

80

70

60

50

40

160

150

140

130

120

110

100

90

METERS FEET

FEET

FEET

METERS

METERS

200

150

100

50

300

250

200

150

550

500

450

400

350

300

A A'

B B'

C

C'

? ? ?

?

?

North Fork Santiam River

Willamette River

Willamette River

SEA

LEVEL

SEA

LEVEL

Wheatland Ferry Section

QTg

Qg1

Qalc

Qalc

Qalc

Qg1

Qg1

Qg2

Qg2

Qg2 Qg2

Qg2

Qg2

sand

Qff2

Qff2 Qff2

Qff2

Tcr

Tcr

Tm

Primarily silt, clay, and local peat

Primarily clay, claystone, siltstone, and sandstone

Overbank facies

Channel facies

EXPLANATION

Schematic representation 

 of soil thickness

Contact—Queried where 

 highly speculative

Approximate location of 

 boundary between 

 sand and gravel 

 channel facies and 

 overlying silty overbank

Approximate location and 

 depth of well log used 

 for subsurface 

 information

?

Figure 3. Relations of Quaternary geologic units in the study area. (Subsurface geology on basis of stratigraphic exposures 

and drillers' logs [approximate positions and depths indicated]. The section traces are shown on plate 1. 

A–A’, Northern Willamette Valley; B–B’, Southern Willamette Valley; C–C’, Stayton subbasin.)
8 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Geomorphology, Stratigraphy, and Mapping Criteria.—Terrace and pediment treads have heights 

ranging from 5 to more than 100 m above present river 

levels, and locally have multiple distinct levels (fig. 4). 

The thickness of underlying sand and gravel varies; 

commonly it is only a few meters thick or less, especially along the Willamette Valley where such surfaces 

on unit QTg have been locally mapped as pediments 

(Bela, 1979; Roberts, 1984). But elsewhere, drillers’ 

logs indicate extensive areas of much thicker sand and 

gravel. The greatest known thicknesses are the 75 to 

150 m of so-called Troutdale Formation sand and 

gravel southwest of Molalla (Hampton, 1972), 30 to 

60 m of sand and gravel near Corvallis and Philomath 

(Bela, 1979), 30 to 60 m of sand and gravel southeast 

of Eugene, greater than 35 m beneath high terraces 

along the North Fork Santiam River near Lyons, and 

20 to 30 m thick sand and gravel beneath terraces 

south of Stayton (fig. 3, geologic section C–C’).

The distinctive characteristic of these deposits is 

the substantial weathering and pedogenic alteration of 

their uppermost several meters. Soils on the weathered 

terrace gravels are typically classified as Xeric Haplohumults or Ultic Haploxeralfs, indicating that there 

has been extensive leaching of mobile elements. The 

upper few meters of these red and clay-rich soils commonly enclose ghosts of pebbles and cobbles that are 

readily sliced by shovel or knife. Large clasts at 

greater depths within the weathered zone have weathering rinds that almost always exceed 5 mm (millimeters), and are typically 1 to 5 cm (centimeters) where 

unweathered cores can be found. Some exposures 

show horizons cemented by iron or manganese oxides. 

Few sedimentary features are visible, but isolated 

small exposures show that this unit is generally composed of subhorizontal beds of rounded gravel clasts 

in a sand and silt matrix.

Unit QTg was mapped primarily on the basis of 

previous geologic mapping, largely following Piper 

(1942), Allison (1953), Allison and Felts (1956), 

Hampton (1972), and Bela (1979, 1981). Placement of 

contacts on 1:24,000 maps and modifications from 

previous geologic maps was based on topography and 

mapped soils. Common and typically diagnostic soils 

shown in Soil Conservation Service (SCS, now Natural Resources Conservation Service) maps are the 

Nekia, Salkum, Veneta, and Jory series. 

Age.—There are few age constraints on the weathered terrace gravels. Allison (1936) and later workers 

(for example, Beaulieu and others, 1974; Roberts,

WILLAMETTE RIVER MILE

ALTITUDE, IN FEET

-200

200

400

600

800

DISTANCE FROM COLUMBIA RIVER CONFLUENCE, IN KILOMETERS

0 50 100 150 200 250

ALTITUDE, IN METERS

-100

-50

SEA

LEVEL

SEA

LEVEL

50

100

150

200

250 0 50 100 150 200

Willamette

Falls

Confluence of

Middle Fork and

Coast Fork

Northern Willamette Valley

Oregon City gap

Southern Willamette Valley

Corvallis

Salem

Eugene

Willamette and Middle Fork Willamette River Profiles

Top of weathered terrace gravels (unit QTg) and Troutdale Formation (unit QTt) 

Bedrock surface

Figure 4. Positions of surfaces of weathered terrace gravels (including Troutdale Formation surfaces near Oregon City gap) 

and subsurface bedrock beneath the Holocene floodplain. (Terrace altitudes from U.S. Geological Survey topographic quadrangles. Data for approximate bedrock altitudes under present river course were derived from drillers' logs and channel 

exposures. Distance from the Columbia River confluence [“valley kilometer”] was measured along the general trend of the 

modern floodplain and does not directly correspond to river miles [see plate 1 for distance indicators].)
Quaternary Deposits in the Willamette Valley 9

1984) have speculated, on the basis of the intense 

weathering, that this unit was deposited in the Early to 

Middle Pleistocene. In the valley of the South Fork of 

the Santiam River, high terraces formed of these 

deposits must be younger than a 4.50.3 Ma basalt 

flow that caps Marks Ridge near Sweet Home (Verplanck, 1985, cited in Walker and Duncan, 1989). 

Other ridge-capping basalts in the Santiam River 

drainage are as young as 2.80.3 Ma (Verplanck, 

1985, cited in Walker and Duncan, 1989). Similar lava

flows in the headwaters of the Middle Fork of the 

Willamette River are as young as 3.23 Ma (Sherrod, 

1991), although their relation to high terrace deposits 

farther downstream is less certain. Weathered terrace 

gravel deposits near Molalla are probably closely 

coeval with Boring Lava erupted from several vents at 

similar altitudes north of the map area near Oregon 

City, where 10 radiometric ages on separate flows 

span 0.4270.026 Ma to 3.1460.062 Ma (Madin, 

1994). Incremental heating Ar-Ar experiments with 

two obsidian clasts collected from a terrace exposure 

along Inman Creek near the west shore of Fern Ridge 

Reservoir yielded ages of 0.7–0.8 Ma, although both 

analyses were discordant, and the ages should be considered tentative (Appendix 1). If these Inman Creek 

dates are accurate, deposition of the weathered terrace 

gravels in the southern Willamette Valley culminated 

after about 0.8 Ma. A 0.420 Ma lahar within gravel 

underlying the valley floor near Eugene (described 

below) likely postdates unit QTg in the southern 

Willamette Valley, thus putting a younger limit on 

the age of the weathered terrace gravels. In summary, 

these weathered terrace deposits could locally be as 

old as 3–5 Ma, but were perhaps mostly deposited 

between 2.5 and 0.5 Ma, and are probably all older 

than about 0.4 Ma.

Origin.—The widespread preservation of multiple 

levels of terraces composed of unit QTg indicates periods of landscape stability after regional aggradation of 

fluvial deposits. Nevertheless, the terraces are too high 

and deformed (fig. 4) to be the product solely of climatic influences as postulated by Allison (1936, 

1953), and their present positions must be partly the 

product of tectonic disturbances within and surrounding the Willamette Valley. On the eastern margins of 

the northern Willamette Valley and in the western 

foothills of the Cascade Range, the terraces are likely 

uplifted by faulting and deformation during Tertiary 

and Quaternary structural development of the northern 

Willamette Valley or by early Pliocene uplift of the 

Cascade Range (Sherrod, 1986; Priest 1990). Along 

the western margins of the southern Willamette Valley, 

however, there is little evidence of late Tertiary or 

Quaternary uplift or faulting, and it is probable that the 

extensive terraces and pediments along the eastern 

foothills of the Coast Range reflect a regional base 

level 10 to 25 m higher than at present. This higher 

base level probably resulted from uplift of the structural arch forming the Salem Hills south of Salem. 

This would be similar to the current situation, where 

uplift along the Portland Hills structural zone has 

caused the 15-m stream discontinuity at Willamette 

Falls (fig. 4), which now controls regional base level 

for the northern Willamette Valley. Local preservation 

of multiple terrace levels (fig. 4; Allison, 1936) may 

indicate separate periods of regionally stable base 

level as the downcutting Willamette River and tributaries were affected by the tectonically rising Cascade 

Range and crossvalley structural zones.

Hydrogeologic Considerations.—The weathered 

terrace deposits are not a regionally important source 

of ground water, although they are a component of the 

Willamette aquifer described by Gannett and Caldwell 

(1998) (fig. 2). Many of these deposits are well above 

valley floors, are only a few meters thick, and, consequently, are above the regional water table (Piper, 

1942, p. 33; Gannett and Caldwell, 1998). In locations 

where unit QTg is thick, the lower portion may be saturated and more permeable because of less weathering, although the clay-rich weathering profile at the 

surface likely restricts infiltration (Piper, 1942, p. 33). 

An area where these older gravels are hydrogeologically important is the broad piedmont flanking the 

Cascade Range foothills southwest of Molalla, where 

many wells penetrate up to 150 m of so-called Troutdale Formation sand and gravel, and produce “small to 

large quantities of water” (Hampton, 1972, p. 42).

Pleistocene Sand and Gravel of the Willamette 

River and major Cascade Range Tributaries (Qg1, 

Qg2)

Underlying the lowlands and valley floors and 

locally inset against unit QTg are varied thicknesses of 

unconsolidated clay, silt, sand, and gravel derived 

from the Coast and Cascade Ranges (fig. 3, geologic 

section C–C’; Gannett and Caldwell, 1998). The upper 

5 to 50 m of these deposits is typically Quaternary-age 

gravel and sand deposited in thin, widespread sheets. 

These coarser facies as well as lower, finer facies 

grade south and east to large sand and gravel fan complexes where major Willamette River tributaries 
10 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

debauch from the Cascade Range (Piper, 1942; Gannett and Caldwell, 1998). Within the Cascade Range 

foothills, Quaternary sand and gravel deposits can be 

further traced up major river valleys as gravelly terrace 

deposits flanking modern floodplains. These sands 

and gravels directly correspond to the Linn Gravel as 

described by Allison (1936, 1953), the Rowland Formation as defined by Balster and Parsons (1969), and 

the Linn Formation of Roberts (1984) (fig. 1), and 

partly coincide with the older alluvium of Piper 

(1942), the Quaternary middle and lower terraces of 

Bela (1979, 1981), and the Quaternary lower terrace of 

Beaulieu and others (1974). Within the northern Willamette Valley, some of these deposits have been speculatively correlated to the Troutdale Formation 

(Glenn, 1965; Hampton, 1972) and Gresham Formation (Trimble, 1963) and have recently been mapped 

as a component of “fluvial and lacustrine(?)” deposits 

of Miocene and Pliocene age (Yeats and others, 1996). 

These sand and gravel deposits are a major component 

of the Willamette aquifer of Gannett and Caldwell 

(1998, fig. 2). Where exposed at the surface, Pleistocene sand and gravel deposits form portions of the 

Winkle and Ingram geomorphic surfaces of Balster 

and Parsons (1968).

We have separated the Pleistocene sand and gravel 

into two separate units; unit Qg2 predates the latest 

Pleistocene (15 to 12.7 ka2

) Missoula Floods and constitutes most of the subsurface Pleistocene sand and 

gravel, whereas unit Qg1 is a comparatively thin sand 

and gravel deposit that postdates the Missoula Floods 

(fig. 3). The distinction between units Qg1 and Qg2 is 

clear for surfaces that are traceable to altitudes below 

100 to 120 m where mappable thicknesses of finegrained Missoula Flood deposits (unit Qff2) obscure 

the braidplain topography of the sand and gravel of 

unit Qg2, but do not cover sand and gravel of unit Qg1

(fig. 3, geologic section B–B’). Such relations are 

found along the Molalla River north of Molalla, the 

fan of the North Fork Santiam River within the Stayton subbasin and near Salem, the fan of the South Fork 

Santiam River northwest of Lebanon, and in the southern Willamette Valley between Eugene and Harrisburg. At higher altitudes in the southern Willamette 

Valley and major tributary valleys, above the mappable extent of Missoula Flood sediment, the distinction 

between pre- and post-Missoula Flood sand and gravel 

deposits is less clear and tentatively inferred on the 

basis of topographic position and soil characteristics. 

Likewise, isolated gravel deposits flanking the modern 

Willamette River floodplain between Albany and 

Salem have been tentatively mapped as Qg1 on the 

basis of topography and soils, although they may be 

younger floodplain deposits. The overall geomorphology, stratigraphy, sedimentology, and hydrogeologic 

characteristics of units Qg1 and Qg2 are similar and 

are described together in the following sections; however, stratigraphic and chronologic details are 

described separately for each unit.

Geomorphology of Pleistocene Sand and Gravel 

Deposits.—In the Willamette Valley and tributary valleys above an altitude of 100–120 m, deposits of units 

Qg1 and Qg2 form broad fans and terraces 5 to 20 m 

above modern stream levels (fig. 5). Below 100-m altitude, deposits of unit Qg2 are buried by Missoula 

Flood sediment, but deposits of unit Qg1 form low terraces and fan surfaces that flank the modern floodplains of the major Cascade Range rivers. Within the 

larger Cascade Range tributary valleys, these units 

commonly form multiple terrace treads separated by 

risers up to 5 m high. These fan and terrace surfaces 

are planar to the eye, but detailed topographic maps 

show a distinct braidplain topography of multiple lenticular bar forms having streamwise lengths of about 1 

km.

Stratigraphy and Sedimentology.—The total 

thickness of Pleistocene sand and gravel is difficult to 

define precisely because the contact between coarse 

deposits and the underlying fine-grained basin fill is 

commonly gradational and complex, marking vertical 

time-transgressive variations in local depositional 

environment as well as lateral, time-equivalent facies 

variations between proximal and distal fan deposits 

(Gannett and Caldwell, 1998). Our best estimates 

from drillers’ logs indicate that near-surface deposits 

of primarily sand and gravel are generally 10 to 30 m 

thick in major tributary valleys, 40 to greater than 100 

m thick at fan apices, and 10 to 20 m thick in the more 

distal portions of larger basins (fig 3; Gannett and 

Caldwell, 1998). More detailed discussion on the 

thickness of unit Qg1 is provided in the section 

“Thickness and Extent of Quaternary Deposits.”

Internal stratigraphy of the upper 30 m of these 

deposits is revealed in a few deep sand and gravel 

excavations and river cuts. Deep exposures into the 

fans show multiple bouldery, cobbly, sandy gravel 

units, and sparse lenses of sand and silt (fig. 6). Distinct gravel units are defined by variations in grain

2“ka” indicates thousands of years before present, and in this 

report refers to ages determined by radiocarbon dating. These ages 

have not been calibrated to calendar years.
Quaternary Deposits in the Willamette Valley 11

WILLAMETTE RIVER MILE

ALTITUDE, IN FEET

200

400

600

DISTANCE FROM COLUMBIA RIVER CONFLUENCE, IN KILOMETERS

0 50 100 150 200 250

ALTITUDE, IN METERS

SEA

LEVEL

SEA

LEVEL

50

100

150

200

0 50 100 150 200

Willamette and Middle Fork Willamette River profiles

Top of post-Missoula Flood sand and gravel (unit Qg1)

Top of pre-Missoula Flood sand and gravel (unit Qg2)

Bottom of post-Missoula Flood sand and gravel (unit Qg1) in subsurface

Top of pre-Missoula Flood sand and gravel (unit Qg2) in subsurface

Willamette

Falls

Confluence of

Middle Fork and

Coast Fork

Geologic section A-A'

Geologic section B-B'

Corvallis

Salem

Eugene

Figure 5. Tops of Pleistocene sand and gravel deposits and the base of the latest Pleistocene (~12 ka) deposits (unit 

Qg1). (Altitudes of surface exposures of units Qg1 and Qg2 from U.S. Geological Survey topographic quadrangles. Subsurface altitudes of the top of the unit Qg2 are from stratigraphic exposures along the Willamette River and from drillers' logs. 

The altitudes of the bases of units Qg1 and Qg2 are inferred from drillers' logs. Distance from the Columbia River confluence was measured along the general trend of the modern floodplain [“valley kilometer”] and does not directly correspond 

to river miles [see plate 1 for distance indicators].)

size, sorting, and orientation of internal bedding structures, and are typically 2 to 10 m thick. Contacts 

between gravel units are typically marked by a subplanar layer of cobbles or boulders, commonly a clast or 

two thick, that separates oxidized and consolidated 

gravel below from gray, loose, openwork gravel above. 

Zones just below contacts are commonly less permeable, resulting in springs where contacts are exposed in 

dewatered excavations below the regional water table. 

No conclusive evidence of pedogenesis has been found 

below these contacts, although in one locality a burned 

stump, apparently in growth position (fig. 6A), shows 

that these contacts probably represent substantial 

pauses in deposition. Some units, deep in gravel pits, 

are distinctly finer than most, and are primarily composed of plane- and cross-bedded sand and silt.

Within individual gravel units, the stratigraphy 

generally consists of multiple cut and fill structures. 

Bedding is defined by grain size and sorting; well 

sorted openwork gravel generally fills the lower parts 

of the cuts, grading up to compact and generally finer 

gravel with silt and sand filling the interstices (fig. 7). 

Exposures parallel to paleoflow direction commonly 

show 0.2- to 2-m high foresets dipping downstream. 

Cobbles are weakly imbricated within horizontal beds. 

Isolated small sand lenses (generally less than 1 m 

thick) commonly surround accumulations of wood.

Maximum clast diameters are typically 30 to 100 

cm in tributary valleys and near fan apices, but much 

smaller out in the Willamette Valley. Clast diameters 

are typically less than 10 cm in exposures along the 

Willamette River in the southern Willamette Valley 

north of Harrisburg, and less than 5 cm in the northern 

Willamette Valley near Salem. Clast diameters greater 

than 2 cm are rare in the far northern part of the valley, 

where sand is the dominant component.

Sand and Gravel Deposited before the Missoula 

Floods (Qg2).—Sand and gravel deposited before the 

15–12.7 ka Missoula Floods make up most of the 

Pleistocene sand and gravel deposited in the Willamette Valley. These deposits were mapped primarily

on the basis of topography, geomorphic relations with 

Missoula Flood sediment, and NRCS soil maps. The 

mapped distribution of the Clackamas (Typic Argiaquolls, Aquultic Haploxerolls), Courtney (Abruptic 

Argiaquolls), Coburg (Pachic Ultic Argixerolls), and 

Awbrig (Vertic Albaqualfs) soil series were key mapping criteria where the stratigraphic relation to Missoula Flood sediment was not clear. Other soil series

common on these older gravel deposits include Bried-
12 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

80

260

250

240

230

220

210

200

75

70

65

60

400

390

380

370

360

350

340

330

320

120

115

110

105

100

95

METERS FEET

METERS FEET

45,640±3,200

>47,000

12,290±110

12,170±70

3,700±70

60±50

Modern

Tm

Qalc

Qg1

Qg1

Qg2

Qg2

Sandy gravel

Loose sandy gravel

with sand lenses

Cemented sandy gravel with sand lenses

Cemented gravel with sand lenses

Sand, silt, and clay

Sand and silt

Sand and silt

Surface disturbed by gravel mining

Original surface (plowed)

Sand and gravel

Silt

Sandy gravel

Burned

stump

Sand and gravel

A. Walling Sand and Gravel pit near Turner Gap

B. Wildish Sand and Gravel pit near Coburg

Figure 6. Stratigraphic and chronologic information for sections of late Quaternary stratigraphy exposed in deep gravel pits 

in the Willamette Valley. (Vertical lines indicate surveyed sections. Thickness to scale; horizontal distance not to scale, but

everywhere represent distances less than 200 meters. Locations of sections are shown on plate 1; A, Walling Sand and 

Gravel excavation near Turner Gap; B, Wildish Sand and Gravel excavation near Coburg).
Quaternary Deposits in the Willamette Valley 13

120

METERS

390

FEET

380

370

360

350

340

330

320

310

300

290

280

270

115

110

105

100

95

90

85

80

0.418±0.010 Ma

0.426±0.004 Ma

Qalc

Qg1

Qg2 Cemented sand and gravel

Loose sand and gravel

Sand and gravel

Sand and silt

Fine sand and silt

Lahar

Surface disturbed by gravel mining

Strongly cemented sand and gravel

EXPLANATION

Schematic representation 

 of soil thickness

Contact between map 

 units

Boundary between 

 deposits within map 

 unit—Probably 

 represents significant 

 depositional hiatus 

Sample location and 

 radiometric age—See 

 appendices 1 and 3 for 

 details

Location of measured 

 section

 

3,700±70

C. Delta Sand and Gravel excavation near Eugene

Figure 6. Late Quaternary stratigraphy exposed in deep gravel pits in the Willamette Valley. (Vertical lines indicate surveyed sections. Thickness to scale; horizontal distance not to scale, but everywhere represents distances less than 200 

meters. Locations of sections are shown on plate 1; C, Delta Sand and Gravel excavation near Eugene.)—Continued.

well (Ultic Haploxerolls), Conser (Typic Argiaquolls), 

Pengra (Typic Haplaquolls), Dayton (Typic 

Albaqualfs), Holcomb (Mollic Albaqualfs), Salem 

(Pachic Ultic Argixerolls), Oxley (Typic Argiaquolls), 

Malabon (Pachic Ultic Argixerolls), and Sawtell (Ultic 

Argixerolls).

Deposits of unit Qg2 typically have planar surfaces 

or a subtle braided channel morphology where they are 

higher than areas of Missoula Flood deposition and 

exposed on the surface. Widely scattered exposures of 

these deposits generally show 1 to 2 m of sandy silt 

capping cobbly gravel. Weathering profiles are typically 2 to 3 m thick and are characterized by reddening, 

aggregation of individual soil particles into pedogenic 

structures, and incipient zones of clay accumulation. 

Cobbles within the uppermost few meters are typically 

slightly pitted where mineral grains have weathered, 

have reddish coatings of translocated clay and iron 

oxides, and have weathering rinds generally in excess 

of 1 to 2 mm. The most weathered of these surfaces, 

such as the Linn Gravel type section near Stayton 

(Allison, 1953), have reddened weathering profiles
14 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

of about 3 m, argillic horizons (Scott Burns, Portland 

State University, written commun., 1997), and weathering rinds greater than 5 mm on fine-grained volcanic 

cobbles.

In each of two deeper pits near Eugene and Salem, 

the sequence of multiple sand and gravel layers composing unit Qg2 is interrupted by deposits of volcanic 

debris flows, or lahars. At the River Bend Sand and 

Gravel quarry near the southern city limits of Salem, a 

15 m deep pit exposes a gray, pumiceous lahar deposit 

between gravel beds (fig. 8). The top of the lahar 

deposit is 13 m below the original ground surface (altitude 70 m above sea level) and has a maximum 

exposed thickness of 2.0 m. The deposit fills a 30-mwide paleochannel and pinches out laterally between 

gravel units. The lahar deposit grades upward from a 

round-cobble, clast-supported gravel to a massive, 

hard, sandy silt enclosing abundant matrix-supported 

subrounded pumice and angular lithic fragments.

The chemical composition of glass in the pumice 

clasts matches that of a thick pumice-fall deposit from 

the last major explosive eruption of Mount Jefferson 

(Appendix 2). During or shortly after this eruption, a 

lahar flowed at least 120 km down the North Fork Santiam River from the flanks of Mount Jefferson through 

Turner Gap to where it is now exposed near Salem. 

Stratigraphic relations in a trench in eastern Idaho 

show that this Mount Jefferson eruption closely predates a Yellowstone tephra that has a 0.0760.034 Ma 

fission track date (Pierce, 1985), thus indicating that 

the Mount Jefferson lahar is probably 0.042–0.110 Ma.

Similarly in a Delta Sand and Gravel Company 

excavation near the northern city limits of Eugene, a 

prominent lahar deposit is exposed about 25 m below 

the original 115 m altitude ground surface (fig. 6). This 

lahar deposit was first noted by geologists from the 

Oregon Department of Geology and Mineral Industries 

(John Beaulieu, oral commun., 1996). The lahar 

deposit also fills a paleochannel, but pinches out over 

about 30 m between fluvial sand and gravel units from 

its maximum exposed thickness of 2.2 m. The lahar 

deposit consists of indurated, light-gray, ashy sandy

Figure 7. Pleistocene sand and gravel exposed at Walling Sand and Gravel pit near Turner Gap. (Shovel is 

approximately 1 meter long.)

Mount Jefferson lahar

Figure 8. Lahar deposit derived from Mount Jefferson. 

(Lahar is about 1 meter thick, and is exposed about 15 

meters below the land surface in an River Bend Sand

 and Gravel excavation south of Salem. (Shovel is about 

1 meter long.)
Quaternary Deposits in the Willamette Valley 15

silt, supporting gravel-size fragments (about 40 percent by volume) of light-gray, angular, glassy rhyodacite (80 percent), angular black obsidian fragments (20 

percent), and rarer rounded pebbles, cobbles, and 

pumice lapilli of diverse lithologies. A distinct feature 

of this deposit is abundant subrounded to subangular 

clasts of black obsidian having maximum diameters as 

great as 15 cm. The composition and location of this 

deposit indicates a major Cascade Range silicic eruption that produced a lahar that traveled down the McKenzie or Middle Fork Willamette Rivers. A source 

for this deposit is not known, but Ar-Ar incremental 

heating analyses of two obsidian clasts yielded ages of 

0.4180.010 Ma and 0.4260.004 Ma (Appendix 1). 

If the obsidian is coeval with the lahar deposit, which 

we tentatively infer because of its high concentration 

within the deposit and its unweathered appearance, 

these about-0.42-Ma ages provide a minimum constraint on the maximum age of the large gravel and 

sand fan formed by the McKenzie and Willamette 

Rivers in the southern Willamette Valley.

At lower altitudes along the axis of the Willamette 

Valley, erosion by the Willamette River on the outsides 

of several large bends has maintained fresh exposures 

of the top of unit Qg2 buried beneath 1 to 

17 m of Missoula Flood sediment (fig. 9). These exposures, such as those at Irish Bend and River Bend, 

have been the basis for several key studies of the late 

Quaternary stratigraphy of the Willamette Valley 

(Allison, 1936, 1953; Glenn, 1965; Balster and Parsons, 1969). Such exposures in the southern Willamette Valley typically show 2 to 3 m of cobbly gravel 

near river level fining up to cross-bedded and planelaminated sand and silt conformably overlain by a 1- 

to 2-m paleosol formed in clayey silt. In the northern 

valley, exposures of Qg2 are thicker, typically revealing 5 to 10 m of cross-bedded sand and isolated gravel 

lenses up to 2 m thick, capped by a 1- to 2-m thick 

paleosol developed in conformably overlying silt and 

clay (fig. 10). The sand and gravel is typically weakly 

cemented by clay, calcite, and iron oxides (Glenn, 

1965; Balster and Parsons, 1969), locally forming 

resistant ledges of sand and gravel that follow bedding.

At almost all locations where the top of unit Qg2

has been examined, sandy layers contain abundant 

rounded pumice grains. The pumice grains are white 

to light yellow and have diameters ranging from less 

than 1 mm to as large as 2 cm. Within small zones of 

cross-bedded sand, pumice grains locally exceed 90 

percent of the total grains. Most of these pumice 

grains are close compositional matches to three pumice layers and tephras erupted from Cascade Range 

sources primarily between 28 and 23 ka (Appendix 2). 

The youngest of these tephras is 23.2 ka, indicating 

that these sands and gravels were locally deposited 

until at least that time. A radiocarbon date of 22,060

100 14C yr BP3 from grass fragments on top of the 

overlying paleosol at the Wheatland Ferry section (fig. 

10; Appendix 3) appears to tightly constrain the end of 

deposition to between 23 ka and 22 ka.

These results are consistent with a 28,4801,810 

14C yr BP age obtained by Roberts (1984) from wood 

within fluvial sand at an equivalent stratigraphic position along the western margin of the southern Willamette Valley near Monroe. Additionally, Glenn (1965, 

p. 178) reported an age of 34,4103,450 14C yr BP 

from a log 6 m below the modern surface in a nowabandoned pit near Salem. These ages are inconsistent 

with much older age assignments for this unit by 

Trimble (1963, p. 55–56), Balster and Parsons (1969), 

and Glenn (1965) on the basis of an infinite (>40 ka) 

radiocarbon date (at an unspecified location) and the 

seemingly strong development of the capping paleosol. 

Pleistocene Sand and Gravel Deposited after the 

Missoula Floods (Qg1).—A thin but widespread unit 

of sand and gravel that postdates the Missoula Floods 

was mapped on the basis of topography, geomorphic 

relations with Missoula Flood sediment, and soil types 

as mapped by the NRCS. Pleistocene sand and gravel 

deposited after the Missoula Floods has not been 

explicitly recognized in previous work; however, Allison (1953) and Allison and Felts (1956) implicitly 

identified surfaces associated with these deposits by 

mapping an “eroded phase” of the Linn Gravel along 

the South Fork Santiam River near Albany. Similar 

deposits and geomorphic relations are found along the 

Molalla, North Fork Santiam, McKenzie and Willamette Rivers where gravel terraces at altitudes below 

the general limits of Missoula Flood deposition are not 

covered by Missoula Flood deposits.

Like the older sand and gravel of unit Qg2, these 

deposits also form planar surfaces above the modern

3. 14C yr BP” indicates radiocarbon years before present, 

where present is A.D. 1950. Stated uncertainty 1 on basis of 

combined measurements of the sample, background, and modern 

reference standards. Complete data for all radiocarbon age analyses performed in this study are given in Appendix 3.
16 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

METERS

14

0

Silt

Sand

Paleosol

Modern soil

Pleistocene

sand and gravel

(unit Qg2);

approximately

28-22 ka

Missoula Flood

deposits

(unit Qff2);

approximately

15-12.7 ka

Gravel gravel clayey silt Clayey silt

Clay clay

EXPLANATION

Contact between

 map units

Stratigraphic boundary

 within map unit, likely

 representing depositional

 hiatus. Approximately

 shown for Missoula

 Flood deposits

Figure 9. Pleistocene deposits exposed on the east bank of the Willamette River at river mile 102.5 near 

Sidney. (More than 10 beds of fine-grained Missoula Flood deposits [unit Qff2] overlying sand and gravel of 

unit Qg2 are shown.) 

 floodplain (figs. 3 and 5). Surfaces formed of unit Qg1

deposits are generally distinguishable from younger 

deposits by their clear braidplain morphology that is 

noticeably distinct from the meandering- and anastomosing-channel topography of the modern floodplains 

of most of the major rivers, although some higher-gradient reaches of the present rivers are transitional 

between meandering and braided, and the flanking

floodplain deposits of these higher-gradient reaches 

also have morphologies transitional between meandering and braided. The distinction between surfaces 

formed of unit Qg1 and modern floodplain deposits 

is also slightly blurred in the southern Willamette Valley where Pleistocene surfaces composed of units Qg1

and Qg2 have been historically flooded and perhaps 

mantled by thin veneers of younger sediment (fig 3,

geologic section B–B’; Parsons and Herriman, 1969). 

The contrast between surficial deposits of unit Qg1 and 
Quaternary Deposits in the Willamette Valley 17

METERS

METERS

METERS

METERS

METERS

METERS

Weston Landing

RM 59.1

River Bend

RM 63.5

Wheatland Ferry

RM 73.2

Sidney

RM 102.5 Irish Bend

RM 151.0

Cartney Park

RM 156.0

Northern Willamette Valley

Southern Willamette Valley

90

85

80

85

80

75

70

60

55

50

45

40

35

30

25

55

50

45

40

35

30

25

55

50

45

40

35

30

25

20

20

15

55

50

45

T

T

T

T

T

T

T

T

Trego Hot Springs

(23.2 ka)

and

Summer Lake E

(>23.2 ka; <27.3 ka)

Red Cloud

(<0.071 Ma)

and

Summer Lake E

(>23.2 ka; <27.3 ka)

Tulelake

(>23.2 ka; <27.3 ka)

22,060±100

Mazama

(6.7 ka)

5,860±120

Wono (27.3 ka)

and

Summer Lake E

(>23.2 ka; 

<27.3 ka)

Soil, massive 

and bedded

silt and clay, 

minor sand 

Rythmically-bedded

Missoula Flood

clay, silt, and

minor sand (unit Qff2)

Unidentified

Cross-bedded grey

sand with silt lenses

Fining-up sequence

of cross-bedded

sand and gravel

capped by

paleosol developed

in silt and clay

(unit Qg2)

Laminated silt

Laminated 

silt

EXPLANATION

Soil or paleosol

Contact—Dashed where approximately located

Fluvially transported tephra with identification and age

Airfall tephra with identification and age

Radiocarbon sample with age in radiocarbon years BP

River mile

NOTE: Datum is sea level

T

T

RM

5,860±120

Figure 10. Correlation of stratigraphic sections measured from exposures along the Willamette River showing 

locations of tephra and radiocarbon samples, and the nature of contact between the main body of Missoula Flood 

deposits (unit Qff2) and the Pleistocene sand and gravel that predates the Missoula Flood deposits (unit Qg2). (The 

thin layers of silt and clay capping the Missoula Flood deposits were judged too thin to constitute a separate map 

unit. The laminated silt and cross-bedded grey sand with silt lenses between the Pleistocene sand and gravel of unit 

Qg2 and the Missoula Flood deposits [unit Qff2] are nowhere exposed on the surface and consequently are not a 

map unit. Altitudes for each section are in meters above sea level. Altitudes for River Bend section modified from 

McDowell and Roberts [1987] assuming a river level of 21.6 meters [71 feet]; altitudes of Irish Bend section after 

Roberts [1984]. The Cartney Park section was measured completely. The Sidney, Wheatland Ferry, and Weston 

Landing sections were all measured from river level to at least the base of the rhythmically bedded fine-grained Missoula Flood deposits [unit Qff2] and the absolute altitudes and total thicknesses of these sections were determined 

from the altitude of the river and the tops of the sections as estimated from U.S. Geological Survey topographic 

quadrangles. Locations of sections are shown on plate 1.)
18 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

the slightly older Pleistocene sand and gravel of unit 

Qg2 is even more obscure above the limits of substantial Missoula Flood deposition, but the deposits of unit 

Qg1 seemingly have a slightly more clearly defined 

braidplain morphology than that of the older deposits 

of unit Qg2, which have been apparently thinly covered in many areas by silt and clay from Missoula 

Floods, windblown sediment, and overbank deposits. 

Many of the soils mapped on unit Qg1 deposits are 

also found on adjacent, older sand and gravel deposits; 

however, the Salem and Malabon soil series (both are 

Pachic Ultic Argixerolls) are generally diagnostic of 

unit Qg1 deposits.

Post-Missoula Flood Pleistocene sand and gravel 

was deposited in broad, fan-shaped swaths where each 

of the major Cascade Range tributaries exited the Cascade Range. In addition, terraces of similar deposits 

were formed along the Willamette River between 

Albany and Salem, and along Butte Creek in the 

northern Willamette Valley. Aggradation associated 

with deposition of this unit led to major shifting of 

river courses throughout the Willamette lowland during this period, resulting in both the North and South 

Forks of the Santiam River significantly changing 

their locations of confluence with the Willamette 

River. The South Fork Santiam River at times took a 

more direct route from its fan apex near Lebanon to a 

confluence with the Willamette River at the present 

location of Albany, subsequently switching to its 

present, more northerly route. The North Fork Santiam 

River flowed through Turner Gap during periods of 

deposition of unit Qg1, joining the Willamette River at 

Salem, instead of its present more southwesterly route 

from the apex of its fan near Stayton to eventually join 

the South Fork Santiam River and then 

Willamette River about 25 km upstream of the location of its former Salem-area confluence. These channel changes resulted in removal of much of the finegrained Missoula Flood deposits (unit Qff2) from the 

Stayton subbasin and Salem areas, and in a broad track 

between Albany and Lebanon.

Surface exposures of unit Qg1 typically show 1 to 

2 m of massive silt overlying bedded sandy gravel. 

Pedogenic features are largely confined to the overlying silt, which is typically slightly reddened, and 

locally has a coarse, prismatic structure, but nowhere 

have pedogenic argillic horizons formed. Cobbles 

within the upper few meters are slightly reddened by 

thin and discontinuous coatings of clay and iron 

oxides, and typically have weathering rinds of about 

0.5 mm or less.

The stratigraphy of unit Qg1 deposits was examined most closely at an active Walling Sand and 

Gravel Company excavation near Turner Gap (fig. 

6A). Turner Gap is a narrow pass at the northwest corner of the Stayton subbasin through which Mill Creek 

presently flows, but in the past has occasionally contained the North Fork Santiam River when it flowed 

northwest out of the Stayton subbasin and joined the 

Willamette River near the present location of Salem. 

The North Fork Santiam River last flowed through 

Turner Gap sometime after deposition of Missoula 

Flood sediment, leaving cobbly gravel deposits and 

carving scarps into Missoula Flood sediment in the 

Stayton subbasin and along a 1- to 3-km-wide swath 

northwest through the present site of Salem. Exposures in the 17-m-deep gravel pit at Turner Gap reveal 

at least four 2 to 8 m sand and gravel units separated 

by disconformities that likely represent substantial 

pauses in deposition (fig. 6A). The uppermost unit 

comprises unit Qg1, and is a gray, cobbly sandy 

gravel, typically about 4 m thick, but locally more than 

7 m thick where it fills a paleochannel. The lower 

boundary of this unit is a subtle but clear and continuously traceable contact that separates loose gray gravel 

from an underlying bouldery, cobbly, sandy gravel 

partially indurated by a clay and silt matrix. Where 

undisturbed, the top of the unit is capped by about 1 m 

of massive silt and sand that underlies the land surface. 

From our observations here and at other deep pits, we 

infer that unit Qg1 is the youngest of multiple and distinct sand and gravel units of similar thickness and 

sedimentologic characteristics that have been intermittently deposited during the Pleistocene.

Two radiocarbon ages from fluvially transported 

wood within unit Qg1 at separate locations in the Walling Sand and Gravel pit at Turner Gap yielded mutually consistent ages of 12,290110 and 12,17070 

14C yr BP. These ages are consistent with geomorphic 

relations indicating deposition after the Missoula 

Floods, and demonstrate a latest Pleistocene pulse of 

deposition after the one that produced the 23–22 ka 

surface formed from the youngest deposits of unit 

Qg2. Analyses of wood from deeper units in the 

Turner pit yielded ages of 45,6403,200 and > 47,000 

14C yr BP, indicating that North Fork Santiam River 

has repeatedly occupied this route during the late 

Pleistocene, switching back and forth between its 

present course and the one through Turner Gap. 
Quaternary Deposits in the Willamette Valley 19

The 12.3- and 12.2-ka ages from unit Qg1 at 

Turner Gap (fig. 6A) indicate a short pulse of deposition as the North Fork Santiam River aggraded while 

flowing through Turner Gap, but other similar deposits 

in the Willamette Valley may have formed somewhat 

earlier or later. The regional stratigraphic framework 

constrains the age of unit Qg1 to between the 15- to 

12.7-ka Missoula Floods (Waitt, 1980, 1985; Atwater, 

1986) and the 6.7-ka Mazama tephra (a widely dispersed tephra erupted from the Mount Mazama eruption that formed Crater Lake). Despite this uncertainty, 

we infer that most of these unit Qg1 deposits were 

formed within several hundred years of 12 ka because 

of their limited extent and the absence of multiple surfaces.

Origin of Pleistocene Sand and Gravel Deposits.—The braidplain surface morphologies and internal stratigraphy of multiple, shallow channels indicate 

that units Qg2 and Qg1 were formed during periods of 

channel instability, high sediment supply, and a sediment load consisting primarily of bedload (Church, 

1992). Overall channel morphology was likely driven 

by high rates of sand and gravel delivery to the major 

stream systems, leading to wide and shallow channels 

that were constantly migrating around point bars and 

islands of freshly deposited bedload (see, for example, 

Fahnestock, 1963; Church, 1972). These surfaces, as 

well as the underlying sand and gravel, can be traced 

to large fans emanating from major Cascade Range 

tributaries, indicating that most sediment was derived 

from the Cascade Range (Piper, 1942; Gannett and 

Caldwell, 1998). Contacts between sand and gravel 

units likely record depositional hiatuses and times 

when streams were more incised, similar to the present 

situation of Holocene rivers and floodplains that 

occupy levels lower than adjacent late Pleistocene terraces. Within the southern Willamette Valley, aggradation of the valley fill has episodically continued since 

at least 0.42 Ma, raising the lowland surface by about 

20 m in the vicinity of Eugene (fig. 6C).

The 28- to 22-ka (uppermost Qg2) and 12-ka (unit 

Qg1) pulses of deposition must indicate distinctly different regional environmental conditions in the Cascade Range than at present. Although there is little 

information of the timing of glacial advances in the 

Cascade Range in Oregon, the ages of sand and gravel 

deposition are broadly consistent with times of glacier 

advances in western North America (Porter and others, 1983; Clark and Bartlein, 1995; Swanson and Porter, 1997). The 28- to 22-ka period of deposition 

closely coincides with the maximum late Pleistocene 

extent of alpine ice in Rocky Mountains and with 

more poorly dated alpine ice advances in the Washington Cascade Range in Washington (summarized by 

Clark and Bartlein, 1995). The 12-ka pulse of deposition that formed unit Qg1 is also coincident with a 

minor—but regionally detected—alpine glacier 

advance in the Washington Cascade Range (Swanson 

and Porter, 1997) and Sierra Nevada in California 

(Clark, 1997; Clark and Gillespie, 1997) and a readvance of the Cordilleran Ice Sheet in southern British 

Columbia (Armstrong, 1981; Clague and others, 

1997). The 12 ka aggradation of Willamette Basin rivers seemingly predates an 11- to 9-ka aggradation episode noted by Personius and others (1993) in the 

Oregon Coast Range.

Despite coinciding with times of regionally 

advanced glaciers, it is unlikely that these aggradation 

pulses were derived entirely from sediment produced 

directly by glaciers. Only about 10 percent of the Cascade Range within the Willamette River Basin was 

covered by ice sheets or glaciers during maximum late 

Pleistocene advances (see fig. 3 in Crandell, 1965), 

and a much smaller percentage would have been glaciated at 12 ka. Much of the increased sediment load 

probably resulted from increased hillslope sediment 

production from enhanced landsliding, periglacial processes, and physical weathering during episodes of 

glacial climates.

Hydrogeologic Considerations.—Except for the 

top few meters, Pleistocene sand and gravel of units 

Qg1 and Qg2 are generally saturated and are a principle source of ground water within the Willamette Valley and a major component of the Willamette aquifer 

(Gannett and Caldwell, 1998; Woodward and others, 

1998). Hydrogeologic properties are chiefly controlled 

by sedimentary characteristics such as clast size and 

sorting. These Pleistocene deposits were left by wide, 

shallow, and braided streams that formed broad fans as 

they flowed from the Cascade Range, resulting in a 

subhorizontal stratigraphy of amalgamated ribbons 

and sheets of gravel and sand. Their composition varies from cobbly, sandy gravel in the major tributary 

valleys and fan apices to silt and sand in distal portions 

of the main basins, although particularly coarse layers 

have distal facies of sand and gravel (Piper, 1942; 

Gannett and Caldwell, 1998). The depositional facies 

vary widely, ranging from well sorted openwork 

gravel left in channel thalwegs, to less-sorted bar 

deposits of sandy gravel containing a compact silty 

clay matrix. These facies variations can be observed 

over lateral distances of 10 m or less and vertical 

distances on the scale of meters, and probably control 

hydrogeologic characteristics over distances of a few 
20 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

hundred meters or less (Piper, 1942). This is visible in 

dewatered gravel pits, where most of the seepage into 

a pit will enter from a few well-defined zones (described by Piper as “arteries”) composed of coarse 

channel facies of well sorted sand or gravel. Nevertheless, over horizontal distances of more than a few hundred meters, such facies variations likely even out and 

at these broader scales the Pleistocene sand and gravel 

deposits can probably be considered laterally homogenous with respect to hydrogeologic properties, although there may be some systematic variation with 

respect to paleoflow direction due to greater connectivity of coarser facies in streamwise directions.

Postdepositional diagenesis and compaction are 

also factors likely affecting hydrogeologic properties. 

Deeper and older sand and gravel is noticeably more 

cemented and compact than units near the surface. 

Typically, the upper 5 to 10 m of sand and gravel fails 

to hold vertical faces, collapses into shovels when 

excavated during gravel extraction, and readily disaggregates into individual grains. Deeper sand and 

gravel holds free faces and is more difficult to excavate. The deepest layers exposed, typically 20 to 30 m 

below the surface, are tightly cemented and typically 

break into conglomeratic aggregates rather than individual grains. The cementing agents include silt and 

clay, iron and manganese oxides, and silica or calcium 

carbonate. The varied cementation and consolidation 

of these deposits probably result in an overall decrease 

in permeability at deeper levels, although the distribution of springs within deep pits clearly shows that 

there are zones of relatively high permeability at all 

depths owing to facies variations within sand and 

gravel units and local differences in the degree of 

cementation. Woodward and others (1998, p. 32–35) 

compared drillers’ logs for wells of different depths in 

the Willamette aquifer and concluded that the specific 

yield for wells deeper than 15 m (50 feet) (which are 

likely drawing water primarily from unit Qg2) was less 

than that for shallower wells completed primarily in 

shallower alluvium (mostly units Qg1 and Qalc). As a 

general rule, our field observations are that the 

younger Pleistocene deposits mapped as unit Qg1 are 

looser and less cemented than are unit Qg2 deposits, 

which include the deep and compacted sand and 

gravel layers, although there is substantial variation 

within deposits of both units.

Missoula Flood Deposits (Qfc, Qff1, Qff2)

Most of the lowland of the Willamette Valley is 

blanketed by deposits from multiple floods from Glacial Lake Missoula (fig. 9). Most of these deposits 

consist of subparallel sheets of silt, clay, and sand that 

cover the valley floor and margins to an altitude of 120 

m above sea level. These valleywide deposits of finegrained Missoula Flood sediment have been mapped 

as unit Qff2. They have a Columbia River Basin provenance and commonly enclose isolated pebbles, cobbles, and boulders of granitic and metamorphic 

lithologies that are foreign to the Willamette River 

Basin. Unit Qff2 becomes progressively sandier to the 

north and grades to two bouldery gravel fans near 

Canby at the northern entrance to the Willamette Valley. These gravel fans have been separately mapped as 

unit Qfc. In the northern Willamette Valley, along the 

Willamette River and Labish channel, a lower deposit 

of stratified silt, sand, and clay of probable Missoula 

Flood origin is inset into units Qff2 and Qfc, and has 

been mapped as unit Qff1. Together, these three units 

of Missoula Flood deposits largely correspond to the 

Willamette Silt as defined by Allison (1953), and the 

Willamette Formation of Balster and Parsons (1969). 

They are a component of the older alluvium of Piper 

(1942), and the Willamette Silt hydrogeologic unit of 

Gannett and Caldwell (1998), except for the coarsegrained unit Qfc which Gannett and Caldwell (1998) 

included in the Willamette aquifer hydrogeologic unit. 

Missoula Flood deposits are correlative to the “upper 

Pleistocene lacustrine deposits” mapped by Trimble 

(1963) in the northern Willamette Valley and Portland 

Basin, and Pleistocene “catastrophic flood” deposits in 

the Portland area (Beeson and others, 1989, 1991). 

They typically underlie the Calapooyia and Senecal 

geomorphic surfaces of Balster and Parsons (1968).

Geomorphology and Distribution.—In the northern Willamette Valley, the main body of fine-grained 

flood deposits (unit Qff2) forms planar or slightly 

undulating geomorphic surfaces between 45 and 60 m 

above sea level, and mantles the flanking foothills and 

piedmont surfaces up to an altitude of 120 m above sea 

level before pinching out against older units (Glenn, 

1965). Within the lowlands, the deposits have been 

dissected by as much as 35 m by the Willamette River 

and local tributaries. In the southern valley, the Missoula Flood deposits underlie a remarkably planar and 

undissected surface (Balster and Parsons, 1968) that 

obscures the braidplain topography of underlying 

gravel surfaces to altitudes between 100 and 120 m 

(fig. 11).
Quaternary Deposits in the Willamette Valley 21

WILLAMETTE RIVER MILE

ALTITUDE, IN FEET

200

400

DISTANCE FROM COLUMBIA RIVER CONFLUENCE, IN KILOMETERS

0 50 100 150 200

ALTITUDE, IN METERS

SEA

LEVEL

SEA

LEVEL

50

100

150

0 50 100 150

Willamette River profile

Top of fine-grained Missoula Flood deposits (unit Qff2)

Base of fine-grained Missoula Flood deposits

Willamette

Falls

Northern Willamette Valley Southern Willamette Valley

Salem

Corvallis Geologic section B-B'

Geologic section A-A'

Figure 11. Altitude and thickness of fine-grained Missoula Flood deposits (unit Qff2). (Top altitude taken from U.S. Geological Survey topographic quadrangles; bottom altitude from stratigraphic exposures along the Willamette River and from drillers' logs. Distance from the Columbia River confluence was measured along the general trend of the modern floodplain 

[“valley kilometer”] and does not directly correspond to river miles [see plate 1 for distance indicators].)

Silt and sand deposits of unit Qff1 form surfaces 

inset into deposits of unit Qff2 along the Willamette 

River between the Yamhill confluence and Wilsonville, along the margins of the Labish channel northeast of Keizer, and within the valley of Champoeg 

Creek (described by Glenn [1965, p. 168], but too 

small to be mapped at the scale of plate 1). Almost 

everywhere the surface of unit Qff1 lies at altitudes 

between 40 and 50 m, which is typically 5 to 20 m 

below adjacent surfaces underlain by the main body of 

fine-grained flood deposits (unit Qff2), but above historic flood levels. Deposits of unit Qff1 are of limited 

extent and, along the Willamette River, are locally 

correlative to the “second bottom deposits” of Allison 

(1978). 

The placement of contacts for both of the finegrained Missoula Flood units (Qff1, Qff2) was based 

on topography and soils, and, for the northern Willamette Valley, largely follows that of Glenn (1965). 

In many areas, Missoula Flood deposits of unit Qff2

lap up and ultimately pinch out against older units 

along the margins of the basins. Exposures on the 

basin margins typically show up to 1 m of Missoula 

Flood silt and clay capping older units up to an altitude of 120 m, but Missoula Flood deposits were 

mapped only where they obscure the original morphology of the underlying unit and where mapped 

soils were primarily those typical of flood deposits. 

With these criteria, Missoula Flood deposits are a 

mappable unit up to altitudes between 60 and 110 m in 

most locations. The Amity (Argiaquic Xeric 

Argiabolls), Willamette (Pachic Ultic Argixerolls), 

and Woodburn (Aquultic Argixerolls) soil series are 

strongly associated with fine-grained Missoula Flood 

deposits of units Qff1 and Qff2. Other common soil 

series on Missoula Flood deposits include Aloha 

(Aquic Xerocrepts), Dayton (Mollic Albaqualfs), and 

Holcomb (Mollic Albaqualfs). These are all fine, silty 

soils that show organic material accumulation and bioturbation, slight reddening of the underlying silt, and 

small amounts of pedogenic clay illuviation in the 

upper 1 to 1.5 m.

Coarser-grained Missoula Flood deposits (Qfc) 

are primarily restricted to two fan-shaped sand, gravel, 

and boulder accumulations near Wilsonville and 

Canby that spread southward from low gaps at the 

head of the northern Willamette Valley. The Wilsonville fan originates from a low divide between the 

Tualatin Basin and the northern Willamette Valley 

along the path of Rock Creek (commonly referred to 

as the “Rock Creek gap”), and the Canby fan radiates 

from the southern end of the Oregon City gap, where 
22 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

the Willamette River has incised through the Columbia River Basalt Group (unit Tcr) and Boring Lava 

(unit QTb) at the Portland Hills structural zone at the 

northern margin of the northern Willamette Valley. A 

small deposit of Missoula Flood gravel also partly 

filled the valley of the Tualatin River near its confluence with the Willamette River at Oregon City. Bouldery gravel has been left in large longitudinal, delta, 

and eddy bars (O’Connor, 1993) in the lee of bedrock 

protrusions. These bars typically have smooth planar 

or convex surfaces that contrast with the ragged, “scabland” (Bretz, 1925) topography of nearby bedrock 

outcrops. These deposits have slightly finer equivalents south of the Willamette River, where flow 

through each of the gaps left several square kilometers 

of undulating surfaces near Canby underlain by bouldery, sandy gravel, locally capped by several meters of 

sand and silt. Characteristic are the sandy, gravelly 

soils of the Canderly (Ultic Haploxerolls) and 

Latourell (Ultic Haploxeralfs) series near Canby, and 

Willamette and Salem series soils near Wilsonville. In 

the Canby area, drillers’ logs indicate that these deposits are locally 30 to 35 m thick and are found at altitudes as low as 10 m above sea level.

Stratigraphy and Sedimentology.—The total 

thickness of the main body of fine-grained flood 

deposits (unit Qff2) locally exceeds 35 m in the central 

part of the northern Willamette Valley, but thins 

towards the basin margins and southward; in the 

southern Willamette Valley, deposits are everywhere 

thinner than 10 m (figs. 10 and 11; Allison, 1935, 

1936, 1978; Glenn, 1965; Balster and Parsons, 1969; 

Gannett and Caldwell, 1998). The most complete 

exposures are along the Willamette River where lateral 

channel migration has created clean exposures of late 

Pleistocene and Holocene stratigraphy (figs. 9 and 10). 

Missoula Flood deposits typically overlie a soil developed in older deposits, including the post-Diamond 

Hill paleosol of Balster and Parsons (1969) on top of 

the 28- to 22-ka sand and gravel, but also conformably 

overlie unweathered fluvial sand and gravel within 

parts of the central portions of the northern and southern Willamette Valley (fig 10; Glenn, 1965). Little evidence of erosion is found where flood deposits 

directly overlie the paleosol developed on older sand 

and gravel, but in some areas the basal silt and sand 

beds are channeled into the underlying sand and 

gravel, partially or completely eroding the paleosol. 

The bedded fine-grained flood deposits of unit 

Qff2 have three distinct internal characteristics: (1) 

almost all fresh exposures show remarkably rhythmic 

bedding under proper lighting and moisture conditions 

(fig. 9; Glenn, 1965; Allison, 1935, 1978; Waitt, 

1985), (2) mineralogic analyses demonstrate that the 

sediment is of Columbia River Basin provenance 

rather than Willamette River Basin provenance 

(Glenn, 1965), and (3) the silt beds commonly contain 

outsized angular to subangular clasts of rock types foreign to the Willamette River Basin (Allison, 1935). 

These attributes are identical to those of equivalent 

fine-grained Missoula Flood deposits that have been 

found elsewhere along the Columbia River and its tributaries in Oregon, Washington, and western Idaho 

(Glenn, 1965; Baker, 1973; Allison, 1978; Waitt, 

1980, 1985; Smith, 1993).

The internal stratigraphy, mineralogy, and grain 

size of unit Qff2 has been described in detail by Glenn 

(1965) for the northern Willamette Valley and is summarized and extrapolated to the entire study area as 

follows: 

1. Individual beds within the sequence of finegrained Missoula Flood deposits range from 

less than 5 cm (centimeter) thick to about 1 m, 

and are defined by subtle and gradational 

grain-size variations within each bed and 

locally distinct grain-size variations at contacts between beds. 

2. The thickness and number of observable beds 

varies within the map area. At least 40 beds 

are countable in the central part of the northern Willamette Valley (Glenn, 1965, p. 88), 

but the number diminishes southward and 

towards the lowland margins. About 20 beds 

are readily distinguished at the Sidney section 

(fig. 9), and about 10 beds are visible at the 

Irish Bend section described by Allison 

(1978) in the southern Willamette Valley. At 

the extreme margins of deposition, such as the 

Cartney Park section (fig. 10), distinct beds 

are not visible, but can be felt when running a 

trowel or knife down the section because of 

subtle changes in grain size influencing the 

hardness of the deposit. 

3. Where individual beds are discernible, they 

are generally thickest near midsection, and 

thin upsection toward the surface, where 

pedogenic processes have masked bedding of 

the upper meter or two. Commonly, the basal 

part of the unit does not have well-defined 

beds and their relative thickness is hard to 

evaluate. 
Quaternary Deposits in the Willamette Valley 23

4. Some sections in the northern Willamette Valley contain scour-and-fill structures where 

multiple beds are unconformably inset within 

steep-sided channels cut into otherwise horizontally bedded deposits (Glenn, 1965).

5. Overall trends in grain size tend to vary 

directly with bed thickness. The thick middle 

beds tend to have slightly coarser materials, 

whereas lower beds, higher beds, and beds 

near the valley margins are typically finer.

6. Within individual beds, Glenn (1965) 

described grading as typically “normal,” 

where each bed fines upwards, or “double,” 

where beds are coarser in their central parts. 

7. Silt and clay within individual beds is generally massive, but is locally laminated. Coarse 

silt and sand components are commonly laminated or cross-bedded between minor scour 

boundaries. Current directions indicated by 

bedding vary, but generally signal southward 

flow in the eastern part of the northern Willamette Valley, and northward flow in exposures 

along the modern Willamette River on the 

western margin of the northern Willamette 

Valley (Glenn, 1965).

Locally, the main body of Missoula Flood deposits 

(unit Qff2) is separated from the underlying paleosol 

by lacustrine(?) and fluvial silt, sand, and gravel of 

primarily Willamette River Basin provenance (figs. 1 

and 10; Glenn, 1965; Balster and Parsons, 1969). This 

intervening unit—Unit II of Glenn (1965) in the northern Willamette Valley, and, presumably, the unexposed 

Wyatt Member of the Willamette Formation 

(described by Balster and Parsons [1969] in the southern Willamette Valley from inspection of shallow borings)—only is exposed in the northern Willamette 

Valley (fig. 10), where it is generally less than 4 m 

thick, and consists of gray, festoon cross-bedded sand 

and intercalated sandy silt lenses. Foresets and current 

ripples within the cross-bedded sand typically indicate 

downvalley (northward) flow. Upsection, the gray 

sand beds become thinner between intervening wavy 

silt lenses until there is an indistinct transition to the 

overlying, rhythmically bedded silts of Columbia 

River Basin provenance. Field identification of the 

contact between Willamette River Basin provenance 

gray sand and silt, and the overlying bedded silts of 

Columbia River provenance is difficult, but such a 

transition, generally corresponding to the zone separating predominantly sand from predominantly silt, 

corresponds to a gradual change between Willamette 

River Basin provenance and Columbia River Basin 

provenance (Glenn,1965, p. 75–87). 

Fluvially reworked pumice and airfall tephra is 

exposed within Glenn's Unit II at the River Bend section (Appendix 2, Glenn, 1965, p. 83–84, Richard 

Waitt, U.S. Geological Survey, written commun., 

1998). The reworked pumice grains match those collected from a similar stratigraphic position 16 km 

upstream at Wheatland Ferry (fig. 10) as well as a 

tephra that lies between the Wono (27,300300 14C yr 

BP) and Trego Hot Springs (23,200200 14C yr BP) 

tephras in a core recovered from Tulelake, California 

(Appendix 2). The airfall tephra at River Bend does 

not match any known tephra layer.

Fine-grained Missoula Flood deposits of unit Qff2

are capped by a variety of thin deposits that are neither 

thick nor continuous enough to warrant mapping at 

this scale, but have been previously postulated to represent major regional Quaternary events (fig. 1). In the 

northern Willamette Valley, these deposits include the 

0- to 30-cm of “gray pebbly silts” described by Glenn 

(1965, p. 87, 193), and in the southern Willamette Valley, the Greenback and Malpass Members of the Willamette Formation as defined by Balster and Parsons 

(1969). The gray pebbly silts of the northern Willamette Valley are massive, contain pebbles of exotic 

and local types, are thicker in swales, and are locally 

absent from topographic highs (Glenn, 1965). Likewise, the Greenback Member was described by Balster and Parsons (1969) as 0 to 1 m of light-gray silty 

material found at the surface of the southern Willamette Valley below altitudes of 120 m. The Malpass 

Member of the Willamette Formation is 0 to 1 m of 

gray clay locally found between the Greenback Member and the bedded flood deposits below (Balster and 

Parsons, 1969), and where exposed at Irish Bend fills 

swales in the underlying flood deposits. At the Cartney Park section, bedded, erratic-bearing silts are 

capped by 2.5 m of massive to locally bedded darkgray silt and clay that contains thin, discontinuous layers of charcoal (5,860120 14C yr BP; Appendix 3), 

and fluvially reworked and airfall Mazama pumice 

and ash (fig. 10).

No exposures of units Qff1 or Qfc were examined 

in this study. Glenn (1965, p. 161–163) describes 

deposits exposed along the Willamette River that are 

possibly equivalent to unit Qff1 as “well stratified silts 

and sands” that are “...not horizontal but follow local 

relief in the underlying sediments.” Allison (1978, 
24 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

p. 194–195) noted exposures of coarse-facies Missoula Flood deposits (unit Qfc), including “poorly 

sorted, bouldery rubble with south-slanting foresets” 

south of the Rock Creek gap near Wilsonville, and 

southwest-dipping foresets of poorly sorted gravel 

beds near Canby. Drillers’ logs of unit Qfc near Canby 

and Wilsonville typically describe 15–35 m of boulders and gravel, locally capped with up to 5 m of sand 

and silt. drillers’ logs of unit Qfc further away from 

the Rock Creek and Oregon City gaps typically 

describe up to 25 m of loose, sandy deposits.

Origin.—The bouldery fan deposits in the northern Willamette Valley (unit Qfc) and the main body of 

rhythmically bedded, Missoula Flood deposits (unit 

Qff2) are the product of multiple late Pleistocene cataclysmic floods from Glacial Lake Missoula (Glenn, 

1965; Allison, 1978; Waitt, 1980, 1985; McDowell, 

1991). Each bed within the fine-grained deposits probably represents an individual flood (Glenn, 1965; Allison, 1978; Waitt, 1980, 1985). As floods traveled 

down the Columbia River valley, a constriction downstream from Portland hydraulically impounded flow to 

as high as 150 m above sea level, resulting in water 

backflooding into the southern Portland and Tualatin 

Basins, from which it spilled southward into the Willamette Valley, primarily through the Oregon City and 

Rock Creek gaps. The south-dipping foresets in the 

bouldery fan deposits (unit Qfc) south of these gaps 

indicate high flow velocities directed southward, and 

the orientation of current structures in the main body 

of Missoula Flood deposits (Qff2), indicate that a 

large, clockwise gyre was established in the northern 

Willamette Valley during many of these floods.

The largest flood(s) left deposits and ice-rafted 

erratics as far south as Eugene and up to an altitude of 

122 m (Allison, 1935), although the number of floods 

that reached that stage is uncertain. About 10 separate 

beds at Irish Bend indicate that at least that many 

floods achieved a stage of at least 85 m above sea 

level, and at least 40 floods achieved a stage of at least 

45 m above sea level at the River Bend section as 

described by Glenn (1965). The total number of floods 

that inundated the Willamette Valley cannot be deciphered accurately from exposures in the map area, but 

more complete stratigraphic records in eastern Washington indicate 60 to 90 late Pleistocene Missoula 

Floods (Atwater, 1986).

The stratigraphic and geomorphic position of unit 

Qff1 lead us to infer that these deposits were laid down 

by later and smaller Missoula Floods than those that 

deposited the more extensive and higher deposits of 

unit Qff2. It is also likely that some of the deposits of 

unit Qff1 were formed or reworked by the Willamette 

River as it reestablished itself within the silt blanketed 

lowlands of the northern Willamette Valley after the 

Missoula Floods that deposited unit Qff2. Glenn 

(1965, p. 161–163) states that the mineralogy of samples collected from the surface of unit Qff1 adjacent to 

the Willamette River between Newberg and Wilsonville “contain a heavy mineral suite similar to that 

found in other Willamette River floodplain samples.”

Glenn (1965, p. 191–192) and Allison (1978) also 

proposed that there were two phases of flooding in the 

Willamette Valley; an early phase of multiple floods 

into a large lake recorded in the rhythmically bedded 

deposits of unit Qff2, and a later phase consisting of a 

single, climactic flood that scoured the gaps at the 

north end of the northern Willamette Valley and left 

the high-altitude erratics and thin pebbly silts and also 

deposited the lower-altitude fine-grained flood deposits of unit Qff1. Reckendorf (1993) modified this 

model, suggesting that the main body of fine-grained 

Missoula Flood deposits (unit Qff2) was from an earlier Pleistocene series of floods and that the thin pebbly silt capping the surfaces of unit Qff2 represented 

multiple late Pleistocene floods. 

These scenarios involving a period of smaller 

floods followed by either single or multiple larger 

floods are inconsistent with stratigraphic and chronologic relations in the Willamette Valley and with 

observations elsewhere along the Missoula Flood 

route. The radiocarbon dates and tephrochronology 

of the underlying sand and gravel indicate that the 

Missoula Flood deposits in the Willamette Valley 

are younger than 22 ka. Because the floodbeds of 

unit Qff2 commonly overlie a paleosol, and there is 

no evidence of a regionally extensive lake either 

between the late Pleistocene sand and gravel of unit 

Qg2 and the bedded Missoula Flood deposits of unit 

Qff1, or within the bedded flood deposits themselves, 

it is most likely that each Missoula Flood inundated a 

largely subaerial landscape. (Local thin deposits of 

laminated silt and fine sand below the Missoula Flood 

deposits at the Wheatland Ferry and Weston Landing 

sections shown in figure 10 likely represent small 

floodplain lakes or ponds rather than an extensive 

water body.) The intervening sand and silt of local and 

transitional provenance observed below the bedded 

flood deposits of Columbia River Basin provenance 

along the Willamette River in the northern Willamette 

Valley may represent deposits of the pre-Missoula 

Flood Willamette River (Glenn, 1965) or, alterna-
Quaternary Deposits in the Willamette Valley 25

tively, may have been left by initial Missoula Floods 

that were relatively less laden with Columbia River 

Basin provenance sediment.

Local and regional evidence of the sequence of 

Missoula Floods is inconsistent with Glenn's (1965) 

and Allison's (1978) conclusion that the last Missoula 

Flood was the largest one. Evidence in eastern Washington (Atwater, 1986) and in the Columbia River Valley east of Portland (O’Connor and Waitt, 1996) 

shows that the last few Missoula Floods were much 

smaller than earlier floods. Indeed, stratigraphic relations in the Willamette Valley, where lower flood 

deposits (unit Qff1) are inset into higher deposits (unit 

Qff2), are identical to relations farther east in the 

Columbia River Valley, where lower deposits of bedded silts clearly postdate deposits of larger floods 

(O’Connor and Waitt, 1996). The massive gray pebbly 

silt that caps the main body of bedded flood deposits 

in the northern Willamette Valley, also attributed by 

Glenn (1965) and Allison (1978) to a climactic flood, 

is probably colluvium and loess, largely derived from 

reworking of Missoula Flood sediment. In the southern Willamette Valley, the capping Greenback and 

Malpass Clay members (fig. 1) of Balster and Parsons 

(1969) are probably a combination of loess and Willamette River Basin provenance fluvial deposits. This is 

clearly the case at the Cartney Park section, where the 

7 ka Mazama tephra and a 5,860120 14C yr BP 

burned horizon within fluvial silt layers indicate 

Holocene overbank deposition on top of the finegrained Missoula Flood deposits (fig. 10). The observations that these capping units are generally thicker 

in swales but nowhere more than a few meters thick, 

contain sparse sedimentary structures, and at least 

locally are of Holocene age all point to a local origin 

rather than being deposited by an exceptionally large 

Missoula Flood.

Age.—Radiometric dates in the Willamette Valley 

and Portland Basin offer the following constraints on 

the age of the Missoula Flood deposits (units Qff1, 

Qff2, and Qfc):

1. Missoula Flood deposits in the Willamette 

Valley postdate the top of the paleosol at the 

Wheatland Ferry section from which we 

obtained an age of 22,060100 14C yr BP age.

2. It is unlikely that there were Missoula Floods 

that inundated the Willamette Valley after the 

12,240 330 14C yr BP age obtained by Glenn 

(1965) on peat that accumulated in a closed 

depression at the north end of the Rock Creek 

Gap, or the 12,17070 14C yr BP age obtained 

from North Fork Santiam River gravel that 

forms a surface inset against Missoula Flood 

deposits near Turner Gap.

3. Peat from a bog on Missoula Flood deposits

in the northern Portland Basin at an altitude 

of 60 m above sea level has an age of 13,080

300 14C yr BP (Mullineaux and others, 1978). 

Any subsequent Missoula Floods in the Portland, or consequently Willamette River 

Basins, could not have achieved stages much 

greater than 60 m above sea level.

These age constraints are consistent with observations farther east that Missoula Floods occurred primarily between 15 and 12.7 ka (Waitt 1980, 1985; 

Atwater, 1986). Radiocarbon ages of 13,69595, 

14,480145, and 14,795 150 14C yr BP obtained on 

organic material collected from high-level Missoula 

Flood deposits in the Columbia River valley east of 

Portland suggest that the larger floods may have been 

between 15 and 13.5 ka. (O’Connor and Waitt, 1996). 

Because the deposits of unit Qff1 are all lower than 60 

m above sea level, it is possible that they postdate 

13,080300 14C yr BP

Hydrogeologic Considerations.—The Missoula 

Flood deposits and overlying loess and colluvium are 

largely included in the Willamette Silt hydrogeologic 

unit of Gannett and Caldwell, (1998). The main body 

of fine-grained Missoula Flood deposits (unit Qff2) is 

not used as a major water source; however, in the 

northern Willamette Valley sandy layers in Missoula 

Flood rhythmites and the sand unit between the paleosol and the rhythmites are capable of providing sufficient water for domestic use (Piper, 1942; Price, 

1967a, b; Hampton, 1972). Where sand and silt at the 

base of the rhythmites is exposed, there is commonly 

seepage. Price (1967a, p. 28) reported that porosity of 

the Missoula Flood deposits in the northern Willamette Valley ranges from 41 to 47 percent, but that 

permeability is low. In the southern Willamette Valley, 

Missoula Flood deposits are too thin and fine-grained 

to serve as a ground-water source, although they probably permit recharge to the underlying Pleistocene 

sand and gravel.

An important exception to the overall low permeability of Missoula Flood deposits in the Willamette 

Valley are the two bouldery fans near Canby and Wilsonville. This area was called the “Canby fan” by 

Piper (1942, p. 42) and is included in Gannett and
26 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Caldwell’s (1998) Willamette aquifer hydrogeologic 

unit. Many wells near Canby exploit up to 35 m of 

loose boulder gravel of “considerable water-yielding 

capacity” (Piper, 1942, p. 45).

Holocene Floodplain Deposits of the Willamette 

River and Major Tributaries (Qalc)

The Willamette River and its major tributaries 

have formed channels and floodplains of sand, silt, 

and gravel in swaths up to 6 km wide along valley and 

lowland bottoms. The Holocene floodplain and channel alluvium of the Willamette River and its major 

Cascade Range tributaries (unit Qalc) have been distinguished from Holocene alluvium of smaller streams 

(unit Qalf) because the channel and floodplain alluvium of the large rivers is distinctly coarser than sediment deposited by smaller Cascade Range and Coast 

Range tributaries and are likely to have significantly 

different hydrogeologic properties (Piper, 1942, p. 28). 

The following discussion pertains only to the deposits 

of the Willamette River and its major tributaries (unit 

Qalc).

Holocene deposits of the Willamette River and 

major tributaries partly include the “younger alluvium” of Piper (1942), “Recent alluvium” mapped by 

Allison (1953), “modern floodplain deposits” of 

Glenn (1965), “Recent river alluvium” and “Quaternary lower terrace deposits” of Bela (1979), and “Quaternary alluvium” of Beaulieu and others (1974). 

These deposits underlie the Horseshoe, Ingram, and 

Luckiamute geomorphic surfaces of Balster and Parsons (1968). Glenn (1965, p. 157–163) described 

stratigraphic and textural characteristics of floodplain 

deposits in the northern Willamette Valley, and Reckendorf (1973) reported on general geomorphic and 

soil characteristics of floodplains in the Willamette 

Valley.

Geomorphology.—The Willamette River has been 

channelized, deepened, and narrowed since European 

settlement (Klingeman, 1987; Benner and Sedell, 

1997), but, prior to these modifications, the Willamette River in the southern Willamette Valley was 

anastomosing (as defined by Church, 1992) and had 

multiple anabranches of substantial flow at high discharges around semistable channel islands (Sedell and 

Froggatt, 1984). Annual formation of debris jams constantly reapportioned flow through the channel system 

(Benner and Sedell, 1997). In the northern Willamette 

Valley, the river has more of a meandering pattern (and 

fewer anabranches) that is constantly evolving through 

meander migration and cutoff formation. The major 

Cascade Range tributaries also typically have an overall meandering pattern formed by meander migration 

and cutoffs, in addition to shifting around low, midchannel islands and bars within short braided reaches. 

The highest floodplain surfaces are about 15 m 

above typical summer river stages in the northern part 

of the valley, but become relatively lower farther 

upstream (fig. 12). Lower surfaces are found at various 

elevations above river level, but are not continuously 

traceable for great lengths along river valleys. Except 

for active channel beds and bars, most surfaces are 

covered by a variable thickness of fine sand, silt, and 

clay. Channel bed material diminishes in median size 

from 4.2 cm near Eugene to 1.9 cm at Willamette Falls 

(Klingeman, 1987). Maximum clast size on active bars 

diminishes from about 50 cm where the major tributary rivers enter the Willamette Valley to about 5 cm 

along the Willamette River near Newberg. Holocene 

floodplain surfaces are generally distinguished by 

their meander-scroll topography of arcuate ridges and 

swales (Reckendorf, 1973; Bela, 1979) that contrasts 

with the more planar topography of adjacent Pleistocene sand and gravel deposits and Missoula Flood

sediment. Common soils on Holocene floodplain surfaces include the Camas, Newberg, Cloquato, Chapman, and Chehalis series, which are all Cumulic Ultic 

Haploxerolls or Fluventic Haploxerolls. Mapping of 

Holocene floodplain deposits largely followed Piper 

(1942), but precise placement of contacts was based 

on 7.5-minute topographic maps and NRCS soils 

maps.

Stratigraphy and Sedimentology.—Exposures 

created by recent bank erosion along the Willamette 

River reveal loose, openwork, imbricated gravel fining 

up to top strata of sand, silt, and clay that are commonly deposited in sequences that thin and fine 

upward (fig. 13). Long bank exposures show lateral 

facies variations such as gravelly channel facies grading to silty and sandy overbank facies. drillers’ logs 

and river exposures along the Willamette River show 

that coarse channel deposits of sand and gravel are 

generally restricted to within 3 m above summer river 

stages; higher deposits are primarily overbank materials such as fine sand, silt, and clay. In the northern 

Willamette Valley, the overall composition of floodplain sediment is about evenly divided between sand, 

silt, and clay, but there is great variation from site to 

site (Glenn, 1965, p. 138–140). 

Age.—Current floodplains are locally set into 12-

ka sand and gravel of unit Qg1 and 15- to 12.7-ka Mis-
Quaternary Deposits in the Willamette Valley 27

WILLAMETTE RIVER MILE

ALTITUDE, IN FEET

SEA

LEVEL

SEA

LEVEL

200

400

600

DISTANCE FROM COLUMBIA RIVER CONFLUENCE, IN KILOMETERS

0 50 100 150 200 250

ALTITUDE, IN METERS

50

100

150

200 0 50 100 150 200

Willamette and Middle Fork Willamette River profiles

Lower Holocene floodplain surfaces

Bedrock (under Holocene floodplain)

Base of Holocene floodplain deposits (unit Qalc)

Highest Holocene floodplain surface 

Willamette

Falls

Confluence of

Middle Fork and

Coast Fork

Geologic section A-A'

Geologic section B-B'

Corvallis

Salem

Eugene

Figure 12. Positions of Holocene floodplain surfaces, the base of Holocene deposits, and bedrock beneath Holocene 

deposits. (Floodplain altitudes from U.S. Geological Survey topographic quadrangles. Bedrock altitudes from channel exposures and well logs. Bottom altitudes of the Holocene deposits are inferred from drillers' logs. Distance from the Columbia 

River confluence was measured along the general trend of the modern floodplain [“valley kilometer”] and does not directly 

correspond to river miles [see plate 1 for distance indicators].) 

soula Flood deposits (units Qff1, Qff2, and Qfc) and, 

therefore, must be largely of Holocene age. Eleven 

radiocarbon ages collected from four exposures of 

floodplain sediment in the southern Willamette Valley 

all yielded ages less than 4 ka (Appendix 3). There 

were no obvious exposures of 7-ka Mazama tephra 

seen during examination of most of the Willamette 

River between Harrisburg and Newberg, although 

likely Mazama tephra has been seen in a floodplain 

gravel pit near Albany (Edward Taylor, Oregon State 

University, oral commun., 1997), and within a channel 

fill of organic-rich clay exposed in a side channel in 

the northern Willamette Valley (Glenn, 1965, p. 161). 

Collectively, these observations indicate that the modern floodplains are formed of deposits laid down during at least the last 7,000 years, but most deposits near 

the present land surface and river course are younger 

than 4 ka.

Origin.—The morphology, stratigraphy, and chronology of floodplain sediment all imply lateral and 

vertical accretion of overbank and channel materials 

deposited by actively meandering and shifting rivers. 

Gravel and sand facies are from bedload transported 

along main channel bottoms and deposited in flanking 

bars. Sand, silt, and clay are primarily overbank 

deposits of suspended sediment. Finer deposits typically accumulate higher and further away from main 

flow paths. Older channel and bar deposits have gradually been covered by finer and finer deposits as channels migrated away or completely changed course to 

more distant paths. Floodplain surfaces of different 

relative elevations above the channel have likely had 

different histories of channel abandonment and subsequent accumulation of overbank deposits, and do not 

necessarily represent different river elevations, sediment regimes, or surface ages as postulated by Balster 

and Parsons (1968). Several large historic floods 

(notably 1861, 1890, 1943, 1964, 1996) have inundated all or most of the floodplain surfaces (Paula 

Minear, Oregon State University, written commun., 

1998), and probably resulted in local aggradation on 

all floodplain levels. Collectively, the channel and 

floodplain morphology and stratigraphy, as well as 

historical accounts of channel mobility and “thick 

with mud” floods (Benner and Sedell, 1997), indicate 

meandering and anastomosing river systems with 

high suspended sediment loads (Church, 1992). 

The Holocene morphology and sediment transport

characteristics of the Willamette River and major 

tributaries were clearly much different under natural 
28 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Figure 13. A measured stratigraphic section, and Holocene fluvial deposits exposed along the Willamette River at the 

southern end of Bear Island (river mile 140). (The view is southwest [upstream].)

conditions than the braided and bedload dominated 

streams of the late Pleistocene.

Hydrogeologic Considerations.—Holocene sand 

and gravel of the modern floodplains is a major source 

of ground water and is a component of the Willamette 

aquifer as defined by Gannett and Caldwell (1998). 

The Holocene sand and gravel typically has higher 

yields than other geologic units in the Willamette 

Valley (Piper, 1942, p. 27–28, 41–54). Woodward and 

others (1998, p. 29–35) present analyses showing that 

the Holocene floodplain deposits of the Willamette 

River and major tributaries have substantially larger 

values of specific capacity, hydraulic conductivity, and 

transmissivity than do underlying alluvial units of the 

METERS

4.4

0

Channel

facies

Overbank

facies

230±120

Unit Qalc

EXPLANATION

Radiocarbon sample

 location and age, 

 in radiocarbon years

 before present

Paleosol or

 bioturbated zone

Stratigraphic boundary

 likely representing 

 depositional hiatus

230±120
Quaternary Deposits in the Willamette Valley 29

Willamette aquifer (primarily units Qg1 and Qg2). As 

with the Pleistocene sand and gravel, the hydrogeologic properties of the Holocene sand and gravel are 

largely controlled by local and regional facies variations. These deposits are young enough, however, that 

postdepositional alteration and compaction are not 

important factors controlling hydrogeologic properties. 

The arrangement of permeable and low-permeability materials appears to be markedly different for 

Holocene floodplain deposits than for the Pleistocene 

sand and gravel. Drillers’ logs and bank exposures 

show that the meandering and anastomosing rivers of 

the Holocene have left tortuous ribbons of well-sorted 

gravel and sand separated horizontally and vertically 

by fine-grained overbank deposits. Similar to current 

river dimensions, the coarse-grained channel facies in 

the subsurface are typically several tens of meters 

wide, and 1 to 3 m thick. Overbank deposits of silt, 

clay, and minor sand typically underlie much of the 

floodplain and may restrict ground-water flow 

between individual ribbons of coarse-grained channel 

facies deposits. Grain size within channel-facies 

deposits diminishes downstream, from cobbles and 

gravel within the major tributary valleys and where 

tributaries emerge from the Cascade Range foothills, 

to sand and gravel in more distal portions of the 

Willamette lowlands. Nevertheless, the channel 

facies are everywhere well-sorted, loose, and likely 

to be highly permeable. 

On a basinwide scale, Holocene sand and gravel 

deposited by the Willamette River and its major tributaries can probably be considered a homogenous unit 

for most ground-water analysis purposes (see, for 

example, Piper, 1942, p. 45). At floodplain-width 

scales, however, the bimodal arrangement of channel 

and overbank facies probably creates highly variable 

permeabilities. At these more local scales, facies variations between and within channel and overbank 

deposits likely control ground-water flow patterns, 

influencing processes such as solute transport, 

hyporheic flow, and interactions between surface 

water and ground water. Locations where subsurface 

channel facies intersect current river channels are 

likely to be zones of substantial exchange between 

ground water and surface water.

Other Quaternary Map Units

Three other units of Quaternary age have been distinguished in the map area. These units are generally 

of small extent and of uncertain or broad ages, and 

have not been studied closely.

Basin Fill (Qbf).—Along the lowland margins are 

small basins and areas that have accumulated clay, silt, 

sand and minor gravel from the adjacent hillslopes and 

small drainages. In the southern Willamette Valley, 

these areas include numerous small basins along the 

western and eastern margins of the Willamette lowlands, as well as higher parts of the valley floor that lie 

between the Coast and Cascade Range foothills and 

the broad braidplains of coarse-grained deposits left 

by the major rivers. There are also several small basins 

in the Cascade Range foothills between Lebanon and 

Stayton that have been partly filled with fine-grained 

deposits from local drainages. There are no basin-fill 

deposits mapped in the many morphologically similar 

basins in the northern Willamette Valley, because 

these basins are all blanketed by mappable thicknesses 

of fine-grained Missoula Flood deposits (unit Qff2). 

The basin-fill deposits of unit Qbf have been variously 

mapped by previous workers, but are largely a component of the “older alluvium” of Piper (1942) and 

underlie parts of the Luckiamute, Ingram, Winkle, 

Senecal and Calapooyia geomorphic surfaces of Balster and Parsons (1968). Surfaces formed in basin-fill 

deposits typically have clayey montmorillonitic soils 

of the Bashaw (Typic Pelloxererts), Natroy (Aquic 

Chromoxererts), Dayton (Typic Albaqualfs), and 

Awbrig (Vertic Albaqualfs) soil series (Knezevich, 

1975; Langridge, 1987; Patching, 1987). Mapping criteria were primarily topography and soils.

Basin-fill deposits were not systematically examined for this study, but their planar surfaces and geomorphic positions indicate that they are composed of 

fine-grained alluvium derived from adjacent hillslopes 

and drainages that head in the western Cascade Range 

and the Coast Range. Piper (1942, p. 28) described 

some of these deposits as “heterogeneous material that 

is largely earthy.” The locations and geomorphic positions of the basin-fill deposits also indicate regional 

aggradation of extensive portions of the Willamette 

lowland after a period of regional base level substantially below the present valley floor. Likewise, the 

basin-fill deposits along the margins of Willamette 

lowlands in the southern Willamette Valley, including 

along the Long Tom River and adjacent to the Cascade 

Range foothills north of Springfield, appear to fill 

marginal topographic lows created by extensive deposition of coarse-grained deposits in the central axis of 

the southern Willamette Valley from the McKenzie 

and Willamette Rivers. Similar deposits are likely 
30 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

extensive in the subsurface along the margins of the 

northern and southern parts of the Willamette Valley, 

composing a part of the Willamette confining hydrogeologic unit of Gannett and Caldwell (1998), but 

have been mostly covered by fine-grained Missoula 

Flood deposits of unit Qff2.

Landslide Deposits (Qls).—Many slopes of the 

Cascade Range foothills are covered with thick deposits of landslide debris and colluvium. These deposits 

were not systematically mapped for this study, but 

their distribution is reproduced with slight modification from the geologic compilation of Walker and 

McLeod (1991). Local modifications to the extent of 

landslide deposits mapped by Walker and McLeod 

(1991) were made on the basis of deposit expression 

on 7.5-minute topographic maps. An additional large 

landslide deposit was identified at the juncture 

between the Willamette Valley and the Cascade Range 

east of Harrisburg, and a thick mantle of colluvium on 

the Cascade Range foothills east of Salem is mapped 

as unit Qls where it obscures the underlying bedrock 

geology.

Undifferentiated Alluvium (Qau).—Alluvial 

deposits in small tributary valleys in the uplands surrounding the Willamette Valley and outside of the limits of fine-grained Missoula Flood deposits (unit Qff2) 

have not been differentiated with respect to age or sedimentology as part of this study. Also undifferentiated 

are the Holocene and Pleistocene deposits of the major 

tributaries in their upper reaches within the map area 

(primarily above the reservoirs). The distribution and 

extent of unit Qau was defined on the basis of topography. The distinction from basin-fill deposits (unit Qbf) 

is locally arbitrary, but unit Qau was primarily mapped 

in narrow valleys rather than wide, flat-bottomed 

basins and valleys. Unit Qau was mapped only outside 

the limits of Missoula Flood deposits, where finegrained deposits of the smaller tributaries (unit Qalf) 

that postdate the 15–12.7 ka Missoula Floods cannot 

be readily distinguished from older tributary deposits.

THICKNESS AND EXTENT OF 

QUATERNARY DEPOSITS

A primary aim of the Willamette Ground-Water 

Study is to develop a numerical ground-water model 

for the Willamette Valley to simulate effects of management scenarios on ground-water flow. To accurately simulate ground-water flow, understanding of 

the distribution and thickness of hydrogeologic units is 

required. Gannett and Caldwell (1998) described the 

distribution and thickness of the “Willamette aquifer,” 

a coarse-grained basin-fill unit, which includes the 

Quaternary units QTt, QTg, Qg2, Qg1, Qfc, and Qalc 

defined in this report (fig. 2). Many of these Quaternary units within the Willamette aquifer have distinctly different hydrogeologic properties due to (1) 

grain-size characteristics, (2) degree of weathering, 

compaction, and cementation, and (3) internal facies 

architecture. For example, Woodward and others 

(1998, p. 52) noted that the coarse-grained deposits in 

the floodplains of the Willamette River and major tributaries (largely corresponding to unit Qalc) were more 

permeable than the rest of the Willamette aquifer. 

Of the Quaternary geologic units defined in this 

study, we judge that two units of regional extent are 

likely to be generally more permeable than other Quaternary units and we have further evaluated their subsurface extent and thickness. The Holocene floodplain 

deposits of the Willamette River and major tributaries 

(unit Qalc) have been identified by Piper (1942) and 

Woodward and others (1998) as having the greatest 

permeability within the Willamette Valley. In our analysis of the thickness of unit Qalc, we have only considered the sand and gravel facies, assuming that the 

several meters of overlying sand, silt, and clay overbank deposits are much less permeable and perhaps 

above the regional water table. We also infer that the 

Pleistocene sand and gravel that postdates the Missoula Floods (unit Qg1) is more permeable than older 

Quaternary units because it is generally looser and less 

cemented than older units. Similar to our analysis of 

unit Qalc, we have estimated the thickness of the sand 

and gravel component of unit Qg1, excluding the 

approximately 1 to 2 m of silt and clay that generally 

caps the sandy gravel at surface exposures.

Methods

Generalized estimates of the thickness of unit Qg1

and the sand and gravel facies of unit Qalc for the map 

area were produced by extrapolating positions of contacts exposed in gravel pits and along riverbanks to the 

rest of the study area on the basis of descriptions of 

subsurface conditions from drillers’ logs. The procedure used was as follows:

1. A series of 29 geologic sections (see, for 

example, fig. 3) was drawn perpendicular to 

the trends of the surface exposures of the postMissoula Flood Pleistocene sand and gravel 

(unit Qg1) and the Holocene floodplain deposits (unit Qalc). Geologic sections were located 
Thickness and Extent of Quaternary Deposits 31

on the basis of proximity to exposures, availability of drillers’ logs, and spacing. Along 

the trend of the Willamette River and tributary 

river floodplains, geologic sections were 

drawn about every 15 km.

2. Subsurface geology for each geologic section 

was locally interpreted from riverbank and 

gravel pit exposures, but more generally 

derived from about 850 lithologic logs of 

water wells, oil and natural gas wells, and 

geotechnical borings. Approximately one-half 

of these logs are from field-located wells 

included in USGS and Oregon Water 

Resources Department databases used to support recent (Woodward and others, 1998; Gannett and Caldwell, 1998) and ongoing (Orzol 

and others, 2000) studies of Willamette Basin 

ground-water conditions. Information from 

field-located wells was further supplemented 

by drillers’ logs from State of Oregon Water 

Well Reports maintained in the USGS Oregon 

District office in Portland, Oregon. These 

wells have not been precisely located by 

USGS personnel, but were located by the 

driller to the quarter section (0.65 km2

) and 

street address. Records of wells that were 

clearly incorrectly located by the driller were 

not used. Locations of wells not precisely on 

the trace of the geologic section were projected to the section trace on the basis of topographic position and the geologic unit in

which the well is located. If either the topographic position or the surficial geologic unit 

at the well location was not clear from the 

available location information, the record was 

not used in constructing the geologic section. 

Because the upper Quaternary units are generally flat-lying, errors due to uncertain location 

and imprecise projection are probably small.

3. For each geologic section, the tops and bottoms of the sand and gravel facies of units Qg1

and Qalc were interpreted from stratigraphic 

exposures and projected drillers’ logs. For 

most of the geologic sections, there is little 

direct stratigraphic information on the bottoms of units Qg1 and Qalc and there was consequently large reliance on drillers’ notes of 

sedimentary characteristics. The base of the 

sand and gravel facies of unit Qalc was 

inferred to correspond to the transition 

between zones typically described by well 

drillers as “clean sand and gravel,” or “gravel 

with sand (or silt) layers” and underlying 

zones of “hard” or “compact” sandy gravel. 

The top of sand and gravel facies of units Qalc 

and Qg1 was identified from drillers’ notes of 

transitions between sand and gravel and overlying silt and clay. The thickness of the Pleistocene sand and gravel that postdates the 

Missoula Floods (unit Qg1) was estimated for 

locations where it forms the surface exposures, and for where it was assumed to exist 

below the Holocene floodplain deposits of 

unit Qalc. Where unit Qg1 was inferred to be 

present below unit Qalc, the top of unit Qg1

was inferred to be equivalent to the base of 

unit Qalc (as depicted in figs. 3, geologic sections A–A’ and B–B’). The base of unit Qg1

was inferred to correspond to drillers’ records 

of a transition to underlying zones of 

“cemented sand and gravel,” which likely corresponds to the older, pre-Missoula Flood, 

Pleistocene sand and gravel of unit Qg2. 

4. For each of the 29 geologic sections, representative altitudes were chosen for:

(a) the top and bottom of the sand and gravel 

facies of unit Qg1 under surface exposures 

of Qg1 (where the top the sand and gravel 

is generally 1 to 2 m below the terrace surface);

(b) the top and bottom of unit Qg1 under surface exposures of unit Qalc (where the top 

of unit Qg1 corresponds to the bottom of 

Qalc); and,

(c) the top and bottom of the sand and gravel 

 facies of unit Qalc.

5. The altitudes of the tops and bottoms of the 

sand and gravel facies for units Qalc and Qg1

determined from these geologic sections were 

plotted along valley profiles for the Willamette, Molalla, North Fork Santiam, South 

Fork Santiam, McKenzie, Middle Fork Willamette, and Coast Fork Willamette Rivers, as 

well as for the late Pleistocene routes of the 

North Fork Santiam River between Stayton 

and Salem through Turner Gap and the South 

Fork Santiam River between Lebanon and 

Albany. Data from geologic sections and 

topography was supplemented by field observations of stratigraphy along channel banks 
32 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

and gravel pits, and by interpretation of additional drillers’ logs to fill gaps in the profiles. 

6. Smooth curves encompassing the observed 

and inferred altitudes for the tops and bottoms 

of the units were drawn parallel to river and 

terrace profiles to provide estimates along valley trends for the (1) top and bottom of sand 

and gravel facies of unit Qg1 under surface 

exposures of Qg1, (2) top and bottom of unit 

Qg1 under surface exposures of Qalc, and (3) 

top and bottom of sand and gravel facies of 

unit Qalc. River and terrace profiles were used 

as a guide to estimate thickness because the 

present- and paleo-river grades defined by the 

river and terrace profiles are likely similar to 

the river grades during the times when the rivers were at altitudes corresponding to the bottoms of units Qalc and Qg1, thus aiding in 

extrapolation between widely spaced constraints on the tops and bottoms of the units.

7. From these curves, altitude contours for the 

tops and bottoms of each unit were drawn and 

digitized into a geographic information system. These contours were drawn normal to 

overall valley trends (parallel to cross sections); thus, there was no information carried 

forward regarding cross-valley trends in the 

tops and bottoms each unit. In general, our 

inference from inspection of drillers’ logs is 

that at the scale of the several-kilometer-wide 

floodplains, lateral variations in the thickness 

of these units are small relative to their lateral 

extent.

8. Within a geographic information system, surfaces were generated to fit the contours representing the altitudes of the tops and bottoms 

of each unit, from which unit thickness was 

calculated. For some small and isolated areas 

of unit Qg1, where thickness could not be 

objectively defined by drillers’ logs or by the 

generated surfaces, thickness values were 

assigned on the basis of the estimated unit 

thickness of nearby areas of unit Qg1.

Results

This analysis process resulted in regional estimates of the thickness of units Qalc and Qg1. In evaluating the results, however, we emphasize that the 

thickness estimates were derived from widely scattered exposures and interpretation of sometimes 

imprecise drillers’ logs. Consequently, the resulting 

thickness maps (figs. 14 and 15) only portray highly 

generalized patterns in unit thickness and should not 

be used for site-specific estimates of the thickness of 

either unit Qalc or Qg1. Nevertheless, at a broader 

scale that is appropriate for incorporating into regional 

ground-water flow models, these thickness estimates 

do show regional variations in the thickness of highly 

permeable components of the Willamette aquifer.

Thickness of Sand and Gravel Facies of Holocene 

Floodplain Deposits (Qalc)

The thickness of the sand and gravel facies of the 

Holocene floodplain deposits is everywhere less than 

15 m (fig. 14). Holocene sand and gravel is generally 

thickest under the Willamette River floodplain in the 

northern Willamette Valley, where it is typically 5 to 

10 m thick, but is nearly 15 m thick near Salem. Along 

the Willamette River floodplain in the southern Willamette Valley, Holocene sand and gravel is typically 

less than 5 m thick, and is thin or absent where the 

Willamette River flows on or near bedrock near 

Eugene. Within the major tributary valleys, the 

Holocene sand and gravel is generally less than 10 m 

thick. 

Estimates of the thickness and extent for the 

Holocene floodplain deposits could be improved with 

additional information on the distribution and chronology of subsurface deposits. Nevertheless, the distinct 

difference in the morphology, sedimentology, and 

facies architecture between the meandering river 

deposits of the Holocene and the underlying and adjacent deposits of the braided stream systems of the 

Pleistocene channel is helpful in making these thickness and extent estimates, especially for the floodplain 

of the Willamette River where the distinction between 

Pleistocene and Holocene river pattern is most pronounced. In major tributary valleys, however, many 

reaches of the present rivers are transitional between 

braided and meandering patterns, and it is more difficult to separate Holocene from Pleistocene deposits 

solely on the basis of morphology and sedimentology. 

Thickness of Pleistocene Sand and Gravel that 

Postdates the Missoula Floods (Qg1)

The post-Missoula Flood Pleistocene sand and 

gravel (unit Qg1) is generally less than 20 m thick

(fig. 15). For portions of the Willamette lowlands 
Thickness and Extent of Quaternary Deposits 33

EXPLANATION

Thickness of floodplain deposits 

(Qalc), in meters

0

10

5

14

Unit outline—unshaded 

area is extent of Qg1 unit 

(See figure 15).

Base composited from USGS digital line graphs and 

other digital information. Universal Transverse Mercator 

projection, Zone 10, 1927 North American Datum

CLACKAMAS

WASHINGTON

POLK

LINN 

LANE

MARION 

YAMHILL 

BENTON

Study area

boundary

Willamette

basin boundary

Woodburn

St Paul

Canby

Aurora Butteville

Oregon

City

West Linn

Newburg

Tualatin

Mount Angel

McMinnville

Amity

Keizer

SALEM

Dallas

Monmouth

Buena

Vista

Independence

Albany

Stayton

Lebanon

Corvallis

Sweet Home

Harrisburg

Halsey

Junction

City

Springfield

Eugene

Cottage

Grove

Middle Santiam

River

River

River

Foster

Lake

Green

Peter Lake Santiam

Calapooia Marys

River

R

Tom

WILLAMETTE

Fern

Ridge

Lake

Long

River

Mohawk

River

McKenzie

Middle

Fall

Creek

Fork

Lookout

Point

Lake

Fall Creek

Lake

Dorena

Lake

Cottage

Grove

Lake

Willamette River

Coast Fork

Luckiamute R

Rickreall Creek

RIVER

North

River

Santiam

River

South

North

River

Molalla

River

South

Yamhill River

River

Y amhill

Tualatin

Clackamas

River

River

Pudding

Chehalem Mountains

Willamette

20

5

5

5

5

205

126

99E

99E

99E

99E

99W

99W

99W

99W

22

99

99

20

126

22

123o30' 123o15' 123o 122o45' 122o30'

45o15'

45o00'

44o45'

44o30'

44o15'

44o00'

43o45'

10 20 MILES

0 10 20 KILOMETERS

0

Figure 14. Approximate thickness of the sand and gravel (channel) facies of Holocene floodplain deposits (unit Qalc) of 

the Willamette River and major tributaries. (See text for discussion of methods and uncertainties).
34 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

EXPLANATION

Thickness of sand and gravel (Qg1), 

in meters. Subsurface unit Qg1 is 

beneath unit Qalc (see Figure 14).

10

20

25

10

20

30

38

Surface Subsurface

Base composited from USGS digital line graphs and 

other digital information. Universal Transverse Mercator 

projection, Zone 10, 1927 North American Datum

CLACKAMAS

POLK

LINN 

LANE

MARION 

YAMHILL 

BENTON

Study area

boundary

Willamette

basin boundary

Woodburn

St Paul

Canby

Aurora Butteville

Oregon

City

West Linn

Newburg

Mount Angel

McMinnville

Amity

Keizer

SALEM

Dallas

Monmouth

Buena

Vista

Independence

Albany

Stayton

Lebanon

Corvallis

Sweet

Home

Harrisburg

Halsey

Junction

City

Springfield

Eugene

Cottage

Grove

Middle Santiam

River

River

River

Foster

Lake

Green

Peter Lake Santiam

Calapooia Marys

River

R

Tom

WILLAMETTE

Fern

Ridge

Lake

Long

River

Mohawk

River

McKenzie

Middle

Fall

Creek

Fork

Lookout

Point

Lake

Fall Creek

Lake

Dorena

Lake

Cottage

Grove Lake

Willamette River

Coast Fork

Luckiamute R

Rickreall Creek

RIVER

North

River

Santiam

River

South

North

River

Molalla

River

South

Yamhill River

River

Y amhill

River

River

Pudding

Willamette

20

5

5

5

5

126

99E

99E

99E

99W

99W

99W

99W

22

99

99

20

126

22

45o15'

45o00'

44o45'

44o30'

44o15'

44o00'

43o45'

10 20 MILES

0 10 20 KILOMETERS

0

WASHINGTON Tu

Tualatin alatin

Clackamas

Chehalem Mountains

5

205

99E

123o30' 123o15' 123o 122o45' 122o30'

10 20 MILES

0 10 20 KILOMETERS

0

Unit outline

Figure 15 Approximate thickness of the Pleistocene sand and gravel that postdates the Missoula Floods (unit Qg1). 

(The thickness estimates were calculated separately for [1] areas where unit Qg1 is exposed at the surface and [2] 

where it is inferred to be present, but generally thinner, in the subsurface under the Holocene floodplain deposits of

unit Qalc. See plate 1 for distribution of surface exposures of units Qg1 and Qalc.)

. 
Summary and Conclusions 35

along the Willamette River where unit Qg1 is exposed 

at the surface, unit Qg1 is typically 10 to 15 m thick. 

Under Qg1 surfaces flanking the major tributaries, we 

judge unit Qg1 to be mostly 5 to 20 m thick; the unit 

appears to be thickest in the McKenzie, Middle Fork 

Willamette, and Coast Fork Willamette River Valleys, 

where unit Qg1 is typically between 10 and 20 m 

thick, but locally may be as thick as 35 m. Along the 

temporary post-Missoula Flood route of the North 

Fork Santiam between Stayton and Salem through 

Turner Gap, unit Qg1 is 3 to 15 m thick; and for the 

similarly temporary route of the South Fork Santiam 

between Albany and Lebanon, unit Qg1 is approximately 10 to 15 m thick. Under the Holocene floodplain deposits of unit Qalc, unit Qg1 is generally less 

than 15 m, and in many places is absent or very thin 

because of Holocene erosion or reworking (see, for 

example, fig. 3, geologic section C–C’).

The thickness and extent information for the Pleistocene sand and gravel deposited after the Missoula 

Floods is less certain than for the sand and gravel 

facies of the Holocene floodplain deposits (Qalc). The 

extent of unit Qg1 and its differentiation from older 

sand and gravel deposited before the Missoula Floods 

(unit Qg2) is clear at altitudes below about 120 m 

above sea level, where the presence or absence of a 

cover of fine-grained Missoula Flood deposits (units 

Qff1 and Qff2) provides sure evidence of the age of the 

deposits relative to the Missoula Floods. But above 

120 m, where Missoula Flood deposits are absent and 

the age of deposits is less certain, the extent of unit 

Qg1 is less easily determined. Consequently, for most 

of the major tributary valleys and for some areas of 

higher altitude in the southern Willamette Valley, the 

distribution of Pleistocene sand and gravel deposited 

after the Missoula Floods (unit Qg1) is much more 

tentatively mapped on the basis of relative elevation 

and soil and weathering characteristics. Determining 

the thickness of unit Qg1 is also difficult because subsurface boundaries between units Qg1and Qg2 are subtle, and are generally only clear in large exposures 

where it is locally defined by a subplanar layer of cobbles or boulders that separates oxidized and consolidated gravel below from gray, loose, openwork gravel 

above. Most drillers’ reports fail to document this transition, and in many areas the estimated thickness of 

unit Qg1, shown in figure 15, likely includes upper 

zones of older sand and gravel deposits. Thickness 

values for unit Qg1 along the Coast Fork Willamette 

River are the most tentative because of the difficulty in 

discriminating between units Qg1 and Qg2 on the surface and in the subsurface, fewer available drillers’ 

logs, and the generally finer texture of Coast Fork 

deposits. Despite these local and regional uncertainties, the overall thickness and extent information portrayed for unit Qg1 in figure 15 represents a less 

consolidated portion of the Pleistocene sand and 

gravel component of the Willamette aquifer that is 

likely to have hydrogeologic properties slightly different than the more compacted and cemented sand and 

gravel below.

SUMMARY AND CONCLUSIONS

The lowlands and tributary valleys of the Willamette Valley are underlain by five major sedimentary 

units of Quaternary age that each record major geologic and environmental episodes. The character, distribution, and thickness of these deposits also exert 

substantial control on current topography, soil characteristics, and ground-water properties. 

The oldest widespread unconsolidated deposits 

are fluvial sands and gravels (unit QTg) that underlie 

terraces flanking lowland margins and tributary valleys. These deeply weathered sands and gravels are 

not well dated, but were probably mostly deposited 

between 2.5 and 0.5 Ma. The sand and gravel deposits 

likely record climatic events affecting sediment supply 

in the Cascade and Coast Ranges, but the present positions of terrace surfaces undoubtedly reflect postdepositional tectonic deformation—either direct tectonic 

uplift of terrace and piedmont surfaces, or regional 

tectonic controls on local base level. 

The weathered terrace gravels have been isolated 

from subsequent deposition by basin margin uplift, 

channel lowering, or tectonic depression of the main 

Willamette lowlands, which in turn has accommodated as much as 500 m of Tertiary and Quaternary 

lacustrine and fluvial fill that now underlies the main 

valley and lowland floors. Within the lowlands, the 

upper 10 to 50 m of fill is primarily Quaternary sand 

and gravel (units Qg1 and Qg2) deposited primarily by 

braided channel systems in subhorizontal sheets 2 to 

10 m thick. These deposits grade to fans up to 100 m 

thick where major Cascade Range rivers enter the lowlands, and are traced farther upstream as much thinner 

valley trains of coarse gravel flanking the major Cascade Range tributaries. Contained within Pleistocene 

sand and gravel deposits are 0.04–0.10 Ma lahar 

deposits from Mount Jefferson and a 0.42-Ma lahar 
36 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

deposit from an unknown source in the headwaters of 

the McKenzie or Middle Fork Willamette Rivers. 

These ages indicate that sand and gravel deposition in 

the Willamette Valley spans at least the last 0.4 Ma. 

These Pleistocene sand and gravel deposits are a major 

source of ground water, and their hydrogeologic properties are controlled primarily by lateral facies variations within broadly time-equivalent sheets of sand 

and gravel, and secondarily by the increased compaction and cementation of deeper and older deposits. The 

two most recent pulses of deposition culminated about 

23 and 12 ka, producing two mappable units (units 

Qg2 and Qg1, respectively) for which the uppermost 

deposits represent episodes of greater sediment production from the Cascade Range during cooler climates of the late Pleistocene.

The latest Pleistocene sand and gravel of unit Qg1, 

which was deposited at about 12 ka and subsequent to 

the Missoula Floods, is likely to be the most permeable of the Pleistocene sand and gravel deposits 

because it is the least cemented and weathered. This 

unit was deposited in broad swaths following the 

Willamette River and major tributaries, as well as 

along temporary routes of the North Fork Santiam 

River between Stayton and Salem through Turner 

Gap, and the South Fork Santiam River between Lebanon and Albany. To support numerical simulation of 

the ground-water flow system that is being conducted 

as part of the U.S. Geological Survey’s Willamette 

Ground-Water Study, the thickness of the post-Missoula Flood sand and gravel unit was estimated from 

stratigraphic exposures and drillers’ logs. Although it 

was locally difficult to differentiate this unit in the 

subsurface from older Pleistocene sand and gravel, in 

most locations unit Qg1 is inferred to be between 5 

and 20 m thick (fig. 15). The unit is seemingly thickest 

in the McKenzie, Middle Fork Willamette, and Coast 

Fork Willamette River Valleys, where unit Qg1 is typically between 10 and 20 m thick, but locally may be as 

thick as 35 m.

After 12 ka, there was a profound change in sediment and flow regimes of the Willamette River and its 

major tributaries: the Pleistocene braided river systems 

that formed vast braidplains of sand and gravel 

evolved to incised and meandering rivers that are constructing today’s near-channel gravel bars and flanking 

sand- and silt-mantled floodplains (mapped together 

as unit Qalc). Modern floodplains are typically 3 to 6 

km wide, are covered by cumulic soils, and have been 

flooded several times during the past two centuries 

(Brands, 1947). Underlying the silt and sand cover of 

the Holocene floodplains are sequences of channel 

facies that form belts of highly permeable sand and 

gravel separated by overbank facies of less permeable 

fine sand, silt, and clay. The ages of most Holocene 

deposits presently exposed along the Willamette River 

are less than 4 ka, although deposits at depth and further away from the present channel are locally older 

than 7 ka.

The Holocene channel and floodplain deposits of 

unit Qalc are the most permeable of the regionally 

extensive Quaternary units. Similar to the latest Pleistocene sand and gravel of unit Qg1, the thickness of 

coarse facies of the Holocene sand and gravel (unit 

Qalc) was estimated to aid in numerical modeling of 

regional ground-water flow conditions. Almost everywhere, the sand and gravel facies of the Holocene 

floodplain deposits are less than 15 m (fig. 14). 

Holocene sand and gravel is generally thickest in the 

northern Willamette Valley, where it is typically 5 to 

10 m thick, but might be as thick as 15 m near Salem. 

In the southern Willamette Valley and along the major 

tributaries, Holocene sand and gravel is generally thinner than 5 to 10 m.

Between 15 and 12.7 ka, fluvial processes of the 

Willamette River and its Cascade and Coast Range 

tributaries were repeatedly and cataclysmically interrupted by multiple floods from Glacial Lake Missoula. 

These floods locally left over 40 beds of sand, silt, and 

clay derived primarily from the upper Columbia River 

Basin. Total thickness of the fine-grained Missoula 

Flood deposits (units Qff2 and Qff1) locally exceeds 

35 m at lower altitudes in the northern Willamette Valley, but tapers to a thin veneer at altitudes of 100 to 

120 m above sea level along the margins of the northern Willamette Valley and on the margins and higher 

plains in the southern Willamette Valley. The Missoula 

Floods also left two bouldery gravel fans (unit Qfc) 

where strong currents entered the northern Willamette 

Valley through low divides from the north. Missoula 

Flood sediment is only a minor ground-water source 

except for the bouldery fans at the northern end of the 

study area, but the silts and clays left behind by the 

floods form the fertile substrate that supports Willamette Valley agriculture.
References 37

REFERENCES

Allison, I.S., 1935, Glacial erratics in Willamette Valley: 

Geological Society of America Bulletin, v. 46, p. 

675–722.

———1936, Pleistocene alluvial stages in northwestern 

Oregon: Science, v. 83, p. 441–443.

———I.S., 1953, Geology of the Albany quadrangle, Oregon: Oregon Department of Geology and Mineral 

Industries Bulletin 37, 18 p.

———1978, Late Pleistocene sediments and floods in the 

Willamette Valley: The Ore Bin, v. 40, p. 177–191 

and 192–202.

Allison, I.S., and Felts, W.M., 1956, Reconnaissance geologic map of the Lebanon quadrangle, Oregon: Oregon Department of Geology and Mineral Industries 

Map QM–4, scale 1:62,500.

Armstrong, J.E., 1981, Post-Vashon Wisconsin glaciations, 

Fraser Lowland, British Columbia: Geological Survey 

of Canada Bulletin 322, 34 p.

Atwater, B.F., 1986, Pleistocene glacial-lake deposits of the 

Sanpoil River valley, northeastern Washington: U.S. 

Geological Survey Bulletin 1661, 39 p.

Bacon, C.R., 1983, Eruptive history of Mount Mazama and 

Crater Lake Caldera, Cascade Range, U.S.A.: Journal 

of Volcanology and Geothermal Research, v. 18, p. 

57–115.

Baker, V.R., 1973, Paleohydrology and sedimentology of 

Lake Missoula flooding in eastern Washington: Geological Society of America Special Paper 144, 79 p.

Baldwin, E.M., Brown, R.D., Jr., Gair, J.E., and Pease, 

M.H., Jr., 1955, Geology of the Sheridan and McMinnville quadrangles, Oregon: U.S. Geological Survey 

Oil and Gas Investigations Map OM–155, scale 

1:62,500.

Balster, C.A., and Parsons, R.B., 1968, Geomorphology and 

soils, Willamette Valley, Oregon: Corvallis, Oregon 

State University Agricultural Experiment Station Special Report 265, 31 p.

———1969, Late Pleistocene stratigraphy, southern 

Willamette Valley, Oregon: Northwest Science, v. 43, 

p. 116–129.

Beaulieu, J.D., Hughes, P.W., and Mathiot, R.K., 1974, 

Environmental geology of western Linn County, Oregon: Oregon Department of Geology and Mineral 

Industries Bulletin 84, 117 p.

Beeson, M.H., Tolan, T.L, Madin, I.P., 1989, Geologic map 

of the Lake Oswego quadrangle—Clackamas, Multnomah, and Washington Counties, Oregon: Oregon 

Department of Geology and Mineral Industries Geological Map Series GMS–59, scale 1:24,000.

———1991, Geologic map of the Portland quadrangle, 

Multnomah, and Washington Counties, Oregon, and 

Clark County, Washington: Oregon Department of 

Geology and Mineral Industries Geological Map 

Series GMS–75, scale 1:24,000.

Bela, J.L., 1979, Geologic hazards of eastern Benton 

County, Oregon: Oregon Department of Geology and 

Mineral Industries Bulletin 98, 122 p.

———1981, Geology of the Rickreall, Salem West, Monmouth, and Sidney 7-1/2 minute quadrangles—Marion, Polk, and Linn Counties, Oregon: Oregon 

Department of Geology and Mineral Industries Geological Map Series GMS–18, scale 1:24,000.

Benner, P.A., and Sedell, J.R., 1997, Upper Willamette 

River landscape—A historic perspective, in Laenen, 

Antonius, and Dunnette, D.A., eds., River quality—

Dynamics and restoration: Boca Raton, Florida, 

Lewis Publishers, p. 23–47.

Benson, Larry, Burdett, James, Lund, Steve, Kashgarian, 

Michaele, and Mensing, Scott, 1997, Nearly synchronous climate change in the Northern Hemisphere during the last glacial termination: Nature, v. 388, p. 

263–265.

Brands, M.D., 1947, Flood runoff in the Willamette Valley, 

Oregon: U.S. Geological Survey Water-Supply Paper 

968–A, 211 p.

Bretz, J.H., 1925, The Spokane flood beyond the Channeled 

Scablands: Journal of Geology, v. 33, p. 97–115 and 

236–259.

Brownfield, M.E., and Schlicker, H.G., 1981a, Preliminary 

geologic map of the Amity and Mission Bottom quadrangles, Oregon: Oregon Department of Geology and 

Mineral Industries Open-File Report O–81–05, scale 

1:24,000.

———1981b, Preliminary geologic map of the McMinnville and Dayton quadrangles, Oregon: Oregon 

Department of Geology and Mineral Industries OpenFile Report O–81–06, scale 1:24,000.

Church, Michael, 1972, Baffin Island sandurs—A study of 

arctic fluvial processes: Geological Survey of Canada 

Bulletin 216, 208 p.

———Channel morphology and typology, in Carlow, P., 

and Petts, G.E., eds., The rivers handbook: Oxford, 

United Kingdom, Blackwell Scientific Publications, 

p. 126–143.

Clague, J.J., Mathewes, R.W., Guilbault, J.-P., Hutchinson, 

I., and Ricketts, B.D., 1997, Pre-Younger Dryas resurgence of the southwestern margin of the Cordilleran 

ice sheet, British Columbia, Canada: Boreas, v. 26, p. 

261–278.

Clark, D.H., 1997, A new alpine lacustrine sedimentary 

record from the Sierra Nevada—Implications for 

late-Pleistocene paleoclimate reconstructions and 

cosmogenic isotope production rates [abs.]: EOS 

(American Geophysical Union), v. 78, p. F249.
38 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Clark, D.H., and Gillespie, A.R., 1997, Timing and significance of late-glacial and Holocene glaciation in the 

Sierra Nevada, California: Quaternary International, 

v. 38/39, p. 21–38.

Clark, P.U., and Bartlein, P.J., 1995, Correlation of late 

Pleistocene glaciation in the western United States 

with North Atlantic Heinrich events: Geology, v. 23, 

p. 483–486.

Crandell, V.R., 1965, The glacial history of western Washington and Oregon, in Wright, H.E., Jr., and Frey, 

D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton University Press, p. 

341–354.

Crenna, P.A., Yeats, R.S., and Levi, Shaul, 1994, Late Cenozoic tectonics and paleogeography of the Salem 

Metropolitan area, central Willamette Valley, Oregon: 

Oregon Geology, v. 56, p. 129–136.

Dalrymple, G.B., 1989, The GLM continuous laser system 

for 40Ar/39Ar dating—Description and performance 

characteristics: U.S. Geological Survey Bulletin 

1890, p. 89–96.

Dalrymple, G.B., and Duffield, W.A.,1988, High precision 

40Ar/39Ar dating of Oligocene rhyolites from the 

Mogollon-Datil volcanic field using a continuous 

laser system: Geophysical Research Letters, v. 15, no. 

5, p. 463–466.

Davis, J.O., 1985, Correlation of late Quaternary tephra layers in a long pluvial sequence near Summer Lake, 

Oregon: Quaternary Research, v. 23, p. 38–53.

Duffield, W.A., and Dalrymple, G.B., 1990, The Taylor 

Creek Rhyolite of New Mexico: A rapidly emplaced 

field of lava domes and flows: Bull. Volcanology, v. 

52, p. 475–487.

Fahnestock, R.K., 1963, Morphology and hydrology of a 

glacial stream—White River, Mount Rainier, Washington: U.S. Geological Survey Professional Paper 

442–A, 70 p.

Fleck, R.J., and Carr, M.D., 1990, The age of the Keystone 

Thrust: Laser-fusion 40Ar/39Ar dating of foreland 

basin deposits, southern Spring Mountains, Nevada: 

Tectonics, v. 9, no. 3, p. 467–476.

Frank, F.J., 1973, Ground water in the Eugene-Springfield 

area, southern Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper 2018, 65 p.

———1974, Ground water in the Corvallis-Albany area, 

central Willamette Valley, Oregon: U.S. Geological 

Survey Water-Supply Paper 2032, 48 p.

Frank, F.J., 1976, Ground water in the Harrisburg-Halsey 

area, southern Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper 2040, 45 p.

Glenn, J.L., 1965, Late Quaternary sedimentation and geological history of the north Willamette Valley, Oregon: Corvallis, Oregon State University, Ph.D. 

dissertation, 231 p.

Gannett M.W., and Caldwell, R.C., 1998, Geologic framework of the Willamette lowland aquifer system, Oregon and Washington: U.S. Geological Survey 

Professional Paper 1424–A, 32 p.

Gerig, A.J., 1985, Soil survey of Clackamas County area, 

Oregon: U.S. Department of Agriculture, Soil Conservation Service, 293 p.

Hampton, E.R., 1972, Geology and ground water of the 

Molalla-Salem slope area, norther Willamette Valley, 

Oregon: U.S. Geological Survey Water-Supply Paper 

1997, 83 p. 

Hallett, D.J., Hills, L.V., and Clague, J.J., 1997, New accelerator mass spectrometry radiocarbon ages for the 

Mazama tephra layer from Kootenay National Park, 

British Columbia, Canada: Canadian Journal of Earth 

Science, v. 34, p. 1202–1209.

Klingeman, P.C., 1987, Geomorphic influences on sediment 

transport in the Willamette River, in Beschta, R.L., 

and others, eds., Erosion and sedimentation in the 

Pacific Rim: International Association of Hydrological Sciences Publication 165, p. 213–223.

Knezevich, C.A., 1975, Soil survey of Benton County area, 

Oregon: U.S. Department of Agriculture, Soil Conservation Service, 119 p.

———1982, Soil survey of Polk County, Oregon: U.S. 

Department of Agriculture, Soil Conservation Service, 250 p.

———1987, Soil survey of Linn County area, Oregon: U.S. 

Department of Agriculture, Soil Conservation Service, 344 p.

Langridge. R.W., 1987, Soil survey of Linn County area, 

Oregon: U.S. Department of Agriculture, Soil Conservation Service, 344 p.

LoBello, P., Feraud, G., Hall, C.M., York, D., Lavina, P., 

and Bernat, M., 1987, 40Ar/39Ar step-heating and 

laser fusion dating of a Quaternary pumice from 

Neschers, Massif Central, France: The defeat of 

xenocrystic contamination: Chemical Geology, v. 66, 

p. 61–71.

Madin, I.P., 1990, Earthquake-hazard geology maps of the 

Portland metropolitan area, Oregon—Text and map 

explanation: Oregon Department of Geology and 

Mineral Industries Open-File Report O–90–2, 21 p.

———1994, Geologic map of the Damascus quadrangle, 

Clackamas and Multnomah Counties, Oregon: Oregon Department of Geology and Mineral Industries 

Geological Map Series GMS–60, scale 1:24,000.

McDowell, P.F., 1991, Quaternary stratigraphy and geomorphic surfaces of the Willamette Valley, Oregon, in

Morrison, R.B., ed., Quaternary nonglacial geology–

Conterminous United States: Geological Society of 

America, Decade of North American Geology, v. K–

2, p. 156–164.
References 39

McDowell, P.F., and Roberts, M.C., 1987, Field guidebook 

to the Quaternary stratigraphy, geomorphology and 

soils of the Willamette Valley, Oregon: Association of 

American Geographers, Annual meeting, Portland, 

Oregon, 1987, Field trip 3, 75 p.

Merrihue, C. and Turner, G., 1966, Potassium-argon dating 

by activation with fast neutrons: Jour. Geophysical 

Research, v. 71, p. 2852–2857.

Mullineaux, V.R., Wilcox, R.E., Ebaugh, F.W., Fryxell, R., 

and Rubin, Meyer, 1978, Age of the last major scabland flood of the Columbia Plateau in eastern Washington: Quaternary Research, v. 10, p. 67–70.

O'Connor, J.E., 1993, Hydrology, hydraulics, and geomorphology of the Bonneville Flood: Geological Society 

of America Special Paper 274, 83 p. 

O'Connor, J.E., and Waitt, R.B., 1995, Beyond the Channeled Scabland—A field trip guide to Missoula Flood 

features in the Columbia, Yakima, and Walla Walla 

Valleys of Washington and Oregon: Oregon Geology, 

Part I, v. 57, no. 3, p. 51–60; Part II, v. 57, no. 4, p. 

75–86; Part III, v. 57, no. 5, p. 99–115.

Orzol, L.L., Wozniak, K.C., Meissner, T.R., and Lee, D.B., 

2000, Ground-water and water chemistry data for the 

Willamette Basin, Oregon: U.S. Geological Survey 

Water-Resources Investigations Report 99–4036, 

65 p.

Otte, G.E., Setness, K.D., Anderson, W.A., Herbert, F.J., Jr., 

and Knezevich, C.A., 1974, Soil survey of Yamhill 

area, Oregon: U.S. Department of Agriculture, Soil 

Conservation Service, 130 p.

Parsons, R.B., 1979, Stratigraphy and land use of the postdiamond Hill paleosol, western Oregon: Geoderma, v. 

22, p. 67–70.

Parsons, R.B., and Herriman, R.C., 1969, Huploxerolls and 

Agrixerolls developed in recent alluvium, southern 

Willamette Valley, Oregon: Soil Science, v. 109, p. 

299–309.

Patching, W.R., 1987, Soil survey of Lane County area, 

Oregon: U.S. Department of Agriculture, Soil Conservation Service, 369 p.

Personius, S.F., Kelsey, H.M., and Grabau, P.C., 1993, Evidence for regional stream aggradation in the central 

Oregon Coast Range during the Pleistocene-Holocene 

transition: Quaternary Research, v. 40, p. 297–308.

Pierce, K.L., 1985, Quaternary history of faulting on the 

Arco segment of the Lost River fault, central Idaho, in

Stein, R.S., and Buckman, R.C., eds., Proceedings of 

workshop XXVIII on the Borah Peak, Idaho, earthquake: U.S. Geological Survey Open-File Report 85–

290, p. 195–206.

Piper, A.M., 1942, Ground-water resources of the Willamette Valley, Oregon: U.S. Geological Survey WaterSupply Paper 890, 194 p.

Porter, S.C., Pierce, K.L., and Hamilton, T.D., 1983, Late 

Pleistocene mountain glaciation in western United 

States, in Porter, S.C., ed., Late Quaternary environments of the United States, Volume 1, the late Pleistocene: Minneapolis, University of Minnesota Press, 

p. 71–111.

Price, Donald, 1967a, Geology and water resources in the 

French Prairie area, northern Willamette Valley, Oregon: U.S. Geological Survey Water-Supply Paper, 

1833, 98 p.

———1967b, Ground water in the Eola-Amity hills area, 

northern Willamette Valley, Oregon: U.S. Geological 

Survey Water-Supply Paper, 1847, 66 p.

Priest, G.R., 1990, Volcanic and tectonic evolution of the 

Cascade volcanic arc, central Oregon: Journal of Geophysical Research, v. 95, no. B12, p. 19583–19599.

Reckendorf, F.F., 1973, Techniques for identifying floodplains in Oregon: Corvallis, Oregon State University, 

Ph.D. dissertation, 344 p.

Reckendorf, Fred, 1993, Geomorphology, stratigraphy, and 

soil interpretations, Willamette Valley, Oregon, in

Kimble, J.M., ed., Proceedings of the eighth international soil management workshop—Utilization of 

soil-survey information for sustainable land use, Oregon, California, and Nevada (July 11–24, 1992): Soil 

Conservation Service, p. 178–200.

Rieck, H.J., Sarna-Wojcicki, A.M., Meyer, C.E., and Adam, 

D.P., 1992, Magnetostratigraphy and tephrochronology of upper Pliocene to Holocene lake sediments at 

Tulelake, Siskiyou, and Modoc Counties, northern 

California: Geological Society of America Bulletin, v. 

104, p. 409–428.

Roberts, M.C., 1984, The late Cenozoic history of an alluvial fill—The southern Willamette Valley, Oregon, in

Mahaney, W.C., ed., Correlation of Quaternary chronologies: Norwich, Great Britain, Geo Books, p. 491–

504.

Samson, S.D., and Alexander, E.C., 1987, Calibration of the 

interlaboratory 40Ar/39Ar dating standard, MMhb–1: 

Chemical Geology (Isotope Geoscience Section), v. 

66, p. 27–34.

Sarna-Wojcicki, A.M., Bowman, H.R., Meyer, C.E., Russell, P.C., Woodward, M.J., McCoy, Gail, Rowe, J.J., 

Jr., Baedecker, P.A., Asaro, Frank, Michael, Helen, 

1984, Chemical analyses, correlations, and ages of 

upper Pliocene and Pleistocene ash layers of east-central and southern California: U.S. Geological Survey 

Professional Paper 1293, 40 p.

Sarna-Wojcicki, A.M., and Davis, J.O., 1991, Quaternary 

tephrochronology, in Morrison, R.B., ed., Quaternary 

nonglacial geology—Conterminous United States: 

Geological Society of America, DNAG Series, v. K–

2, p. 93–116.
40 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Sarna-Wojcicki, A.M., Meyer, C.E., Bowman, H.R., Hall, 

N.T., Russell, P.C., Woodward, M.L., and Slate, J.L., 

1985, Correlation of the Rockland ash bed—A 

400,000-year-old stratigraphic marker in northern 

California and western Nevada, and implications for 

middle Pleistocene paleogeography of central California: Quaternary Research, v. 23, p. 236–257.

Sedell, J.R., and Froggatt, J.L., 1984, Importance of streamside forests to large rivers—The isolation of the

 Willamette River, Oregon, U.S.A., from its floodplain by snagging and streamside forest removal: 

Internationale Vereinigung für theoretische and 

angewandte Limnologie Verhandlungen, v. 22, p. 

1828–1834.

Sherrod, V.R., 1986, Geology, geochronology, and volcanic 

history of a portion of the Cascade Range between 

latitudes 43–44N, central Oregon, U.S.A.: Santa 

Barbara, University of California, Ph.D. dissertation, 

320 p.

———1991, Geologic map of a part of the Cascade Range 

between latitudes 43–44, central Oregon: U.S. Geological Survey Miscellaneous Investigations Series 

Map I–1891 with accompanying pamphlet, scale 

1:125,000.

Sherrod, D. R., and Pickthorn, L. G., 1989, Some notes on 

the Neogene structural evolution of the Cascade 

Range in Oregon, in, Muffler, L.J.P., Weaver, C.S., 

and Blackwell, D.D., Geological, geophysical, and 

tectonic setting of the Cascade Range: U.S. Geological Survey Open-File Report 89–178, p. 351–368.

Smith, G.A., 1993, Missoula Flood dynamics and magnitudes inferred from sedimentology of slack-water 

deposits on the Columbia Plateau, Washington: Geological Society of America Bulletin, v. 105, p. 77–

100.

Steiger, R.H., and Jager, E., 1977, Subcommission on geochronology—Convention on the use of decay constants in geo- and cosmochronology: Earth and 

Planetary Science Letters, v. 36, p. 359–362.

Swanson, T.W., and Porter, S.C., 1997, New cosmogenic 

isotope ages for the last glaciation in the eastern 

North Cascade Range [abs.]: Geological Society 

of America Abstracts with Program, v. 29, no. 6, 

p. A–109.

Taylor, J.R., 1982, An introduction to error analysis—The 

study of uncertainties in physical measurements: Mill 

Valley, California, University Science Books, 270 p.

Trimble, D.E., 1963, Geology of Portland, Oregon, and 

adjacent areas: U.S. Geological Survey Bulletin 1119, 

119 p. 

Waitt, R.B., 1980, About 40 last-glacial Lake Missoula 

jökulhlaups through southern Washington: Journal of 

Geology, v. 88, p. 653–679.

———1985, Case for periodic, colossal jökulhlaups from 

Pleistocene glacial Lake Missoula: Geological Society of America Bulletin, v. 96, p. 1271–1286.

Walker, G.W., and Duncan, R.A., 1989, Geologic map of 

the Salem 1o by 2 quadrangle, western Oregon: U.S. 

Geological Survey Miscellaneous Investigations 

Series Map I–1893.

Walker, G.W., and MacLeod, N.S., 1991, Geologic map of 

Oregon: U.S. Geological Survey, scale 1:500,000.

Williams, L.H., 1972, Soil survey of the Marion County 

area, Oregon: U.S. Department of Agriculture, Soil 

Conservation Service, 132 p.

Woodward, D.G., Gannett, M.W., and Vaccaro, J.J., 1998, 

Hydrogeologic framework of the Willamette lowland 

aquifer system, Oregon and Washington: U.S. Geological Survey Professional Paper 1424–B, 82 p.

Yeats, R.S., Graven, E.P., Werner, K.S., Goldfinger, Chris, 

and Popowski, T.S., 1996, Tectonics of the Willamette Valley, Oregon, in Rogers, A.M. and others, 

eds., Assessing earthquake hazards and reducing risk 

in the Pacific Northwest—Volume 1: U.S. Geological 

Survey Professional Paper 1560, p. 183–222.

York, D., Hall, C.M.,Yanase, Y., Hanes, J.A., and Kenyon, 

M.J., 1981, 40Ar/39Ar dating of terrestrial minerals 

with a continuous laser: Geophysical Research Letters, v. 8, p.1136-1138.
APPENDIXES

APPENDIX 1–40Ar/39Ar analyses of volcanic materials

We used laser fusion (York and others, 1981) and incremental-heating (Merrihue and Turner, 1966) methods 

of 40Ar/39Ar analysis to determine the ages of volcanic clasts from alluvial deposits in the Willamette Valley. 

Laser-fusion techniques allow dating of single or small numbers of mineral grains, and, for this study, followed 

the procedures of LoBello and others (1987), Dalrymple and Duffield (1988), and Fleck and Carr (1990). 

Approximately six analyses were performed for each sample. The incremental-heating analyses utilized a 

low-blank, tantalum and molybdenum, resistance-heated furnace, and 100 to 200 mg (milligrams) samples. Total 

gas was released in 8 to 15 heating increments. The incremental-heating analyses were performed on the same 

mass spectrometer and using the same argon-extraction system described by Dalrymple (1989). 

Samples for 40Ar/39Ar dating were irradiated for 2 hours in the U.S. Geological Survey TRIGA Reactor 

Facility in Denver, Colorado. An intralaboratory standard sanidine, 85G003, (Taylor Creek Rhyolite, 27.92 Ma) 

was used for calculation of the neutron flux in all irradiations. The age of this monitor mineral is as reported by 

Duffield and Dalrymple (1990), standardized to an average age of 513.9 Ma measured in the U.S. Geological Survey Menlo Park laboratory for interlaboratory standard hornblende, MMhb1 (Samson and Alexander, 1987), and 

our intralaboratory standard biotite, SB-3. Decay and abundance constants for all ages reported are those recommended by Steiger and Jager (1977). 

Summary results are presented in table A1–1; results from the incremental-heating analyses are shown in 

table A1–2. The results of the laser-fusion analyses from the two samples of obsidian from the weathered terrace 

gravels (unit QTg) yielded discordant results, indicating that individual analyses differed by more than 2 and 

that there was probably loss of radiogenic argon following initial cooling of the obsidian. This may have been due 

to weathering. The results from the two samples of obsidian from the Pleistocene sand and gravel (unit Qg2) were 

concordant and yielded mutually consistent results. Step-heating analyses from one of the Inman Creek clasts 

failed to define a distinguishable plateau or isochron.

Table A1–1. Argon(40)-argon(39) ages

[Analyses by Robert J. Fleck. Latitude and longitude given in decimal degrees. ID, identification; Ma, millions of years before present; m, meters]

Sample ID

Location

Laser-fusion 

age1

(Ma)

1

Age represents weighted mean of measurements (Taylor, 1982). The error stated is 1 as judged by the analytical data alone.

Incremental Heating Method2

2

The error stated is 1 as judged by the analytical data alone.

Best estimate3

(Ma)

3

The “final age” and approximate error was determined from final analytical results and subjective consideration of the quality 

of the experiments.

Latitude Longitude Plateau age (Ma) Comments

Isochron age

(Ma)

DSG-2 Delta Sand and Gravel 0.414.015 0.4170.005 0.4190.008 0.4180.010 Obsidian clasts 

within lahar deposits exposed approximately 25 m below 

surface

44.1063N 123.1098W

UBPT-1 0.4140.008 0.4260.003 0.4270.004 0.4260.004

JEO

 12/29/98-1L

Inman Creek 0.9230.015

(discordant4)

4

Individual results from multiple laser-fusion analyses of the sample differed by more than 2.

0.8070.020 0.699.187 0.7500.060 Obsidian clasts 

within weathered 

terrace gravels (unit 

QTg)

44.1095N 123.3257W

JEO 

12/29/98-1M

0.751.250

(discordant4

)

No distinguishable 

plateau

No isochron 

defined

0.750.250

Appendixes 43
Table A1-2. 40Ar/39Ar incremental-heating analysis results [Analyses by Robert J. Fleck. °C, degrees Celsius; ka, thousands of years before present] 

Step 

(°C)

Percent

39Ar

Percent

40Ar

Percent 

36ArCa 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar Age (ka)

Sample DSG-2, Delta Sand and Gravel

450 0.53 3.62 0.32 10.69312 0.3993 0.03499 221130

500 2.12 24.35 .12 3.1993 .1316 .00823 44533

550 4.62 30.09 .99 2.0040 .1685 .00479 34410

600 6.12 49.24 1.24 1.3916 .1064 .00242 3918

650 6.14 54.80 1.53 1.2660 .1073 .00197 3978

700 11.91 64.18 2.25 1.1005 .1093 .00136 4045

750 24.01 71.82 2.87 1.0229 .1026 .00100 4203

775 14.50 67.16 2.38 1.1011 .1062 .00125 4234

800 17.09 62.54 1.99 1.1633 .1068 .00150 4164

825 4.97 60.87 1.57 1.3117 .0985 .00176 4569

850 1.74 12.33 .24 5.6664 .1465 .00169 39927

875 .84 47.86 .73 2.4912 .1145 .00443 68151

950 .95 12.31 .85 3.6721 .3328 .01099 25845

1,050 1.09 33.47 1.77 2.4927 .3610 .00571 47739

1,400 3.38 32.88 .46 2.3626 .0892 .00539 44413

Sample UBPT-1, Delta Sand and Gravel

450 .28 negative .26 5.5245 .2064 .02219 negative

500 1.93 14.96 .64 2.4952 .1650 .00723 21934

550 3.49 30.74 .90 1.8860 .1431 .00446 33912

600 7.39 58.42 1.84 1.2023 .1126 .00172 4116

650 7.32 66.08 2.46 1.0434 .1075 .00123 4046

700 27.60 80.41 4.15 .9108 .0931 .00063 4293

725 14.70 82.67 4.92 .8814 .0953 .00054 4274

750 9.95 77.55 3.68 .9328 .0962 .00074 4235

775 11.08 74.39 2.79 1.0016 .0888 .00089 4365

800 5.82 67.87 1.77 1.0891 .0761 .00121 4337

825 4.52 22.12 .51 3.2812 .1563 .00869 42511

850 1.56 39.56 .63 1.7683 .0822 .00364 40926

875 .84 27.64 .37 2.1456 .0689 .00527 34748

925 .86 19.27 .61 2.9248 .1757 .00804 33047

1,025 1.63 26.30 .44 2.5938 .1012 .00650 39925

1,200 1.05 20.51 .50 4.0151 .1920 .01085 48239

Sample JEO12298-1I, Inman Creek

475 .26 .59 .02 92.8457 .1860 .31241 4071,086

525 .99 9.61 .07 18.1652 .1429 .05560 1,304259

560 1.67 8.96 .09 14.8985 .1426 .04594 997155

610 3.09 6.22 .07 18.6403 .1491 .05920 86695

660 4.13 8.63 .10 13.7689 .1510 .04262 88771

710 5.03 8.15 .10 13.3097 .1473 .04141 81061

760 7.52 7.88 .11 12.8657 .1502 .04015 75647

800 11.08 8.65 .10 13.0348 .1487 .04034 84241

850 10.74 7.96 .10 13.8590 .1488 .04321 82343

900 10.81 7.25 .10 13.8653 .1482 .04356 75143

44 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon
Step 

(°C)

Percent

39Ar

Percent

40Ar

Percent 

36ArCa 40Ar/39Ar 37Ar/39Ar 36Ar/39Ar Age (ka)

Sample JEO12298-1I, Inman Creek—Continued

950 11.36 8.48 0.10 13.8965 0.1480 0.04308 88042

1,000 10.67 8.63 .10 13.9994 .1477 .04333 90243

1050 9.46 9.92 .10 13.9302 .1463 .04251 1,03245

1100 7.00 11.07 .10 13.9935 .1475 .04215 1,15751

1175 4.75 12.69 .09 15.6062 .1432 .04615 1,47867

1260 1.44 12.19 .08 17.8695 .1463 .05314 1,625181

Sample JEO12298-1M, Inman Creek

475 .07 -2.30 .03 82.0042 .3253 .28405 negative

535 .61 .52 .03 43.1678 .1563 .14537 163283

600 1.68 -1.07 .03 40.9656 .1571 .14016 negative

650 3.09 -.12 .03 40.2040 .1597 .13626 negative

700 3.56 .26 .03 39.9197 .1570 .13478 77119

740 4.95 2.23 .03 39.7767 .1462 .13165 650118

775 5.85 1.29 .03 39.5586 .1504 .13218 375118

790 4.52 1.83 .03 39.6248 .1334 .13168 533118

800 4.57 2.98 .03 39.6805 .1415 .13032 869117

810 4.29 2.03 .03 39.9259 .1483 .13242 594118

820 4.52 1.55 .03 39.5350 .1496 .13176 450117

830 4.51 1.42 .03 39.5901 .1475 .13211 414118

840 4.52 1.60 .03 39.5976 .1519 .13190 464118

850 4.52 2.16 .03 39.5002 .1510 .13083 627117

860 4.01 1.61 .03 39.4510 .1512 .13140 467117

870 3.95 2.45 .03 39.5525 .1477 .13061 712117

880 3.71 2.74 .03 39.5939 .1464 .13036 797117

890 3.53 2.34 .03 39.7615 .1487 .13145 682118

900 3.57 3.11 .03 39.7395 .1485 .13034 908117

910 3.53 3.14 .03 39.9974 .1495 .13114 923118

920 3.38 3.24 .03 39.9654 .1483 .13090 952118

930 4.09 3.61 .03 39.8843 .1448 .13014 1,058117

940 3.59 3.98 .03 40.0540 .1456 .13019 1,172118

950 2.70 4.52 .03 40.1443 .1448 .12975 1,333119

965 2.38 4.08 .03 40.2387 .1463 .13066 1,205142

985 2.23 4.20 .03 40.5170 .1502 .13140 1,248147

1,020 2.27 4.16 .03 41.0200 .1447 .13308 1,253147

1,080 2.63 5.13 .03 42.5001 .1445 .13649 1,599140

1,200 3.29 6.84 .03 42.5161 .1431 .13407 2,136129

Table A1-2. 40Ar/39Ar incremental-heating analysis results—Continued [Analyses by Robert J. Fleck. °C, degrees Celsius; ka, thousands of years before present] 

Appendixes 45
46 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

APPENDIX 2–Analytical Methods and Results for Tephra Analysis

Volcanic glass shards separated from macroscopic tephra layers or zones of disseminated pumice sampled from outcrops (table A2–1) were analyzed using methods described by Sarna-Wojcicki and others 

(1984) and Sarna-Wojcicki and others (1985). The polished glass shards were analyzed for Si, Al, Fe, Mg, 

Mn, Ca, Ti, Na, and K. Approximately 15 to 20 shards were analyzed from each sample. Some samples 

contained two or more compositional modes, and each mode was analyzed separately (table A2–2). 

Results of analyses were compared with our database of approximately 4,200 previously analyzed samples 

of volcanic glasses from upper Neogene and Quaternary tephra layers collected within the conterminous 

Western United States and from bottom sediments of the adjacent Pacific Ocean. The best matches were 

identified using numerical and statistical programs (SIMANAL; Sarna-Wojcicki and others, 1984), which 

were then further examined for petrographic similarity and for stratigraphic position and sequence (SarnaWojcicki and Davis, 1991). Final interpretation of potential correlation of sampled tephras with known 

tephras (table A2–1) was made on the basis of (1) chemical composition of volcanic glass (excluding or 

minimally weighting those elements present in concentrations close to detection limits), (2) petrographic 

characteristics, and (3) stratigraphic position. 

Table A2-1. Willamette Valley tephra and pumice correlations

[Samples from sections exposed along Willamette River (shown in figure 10) are listed in downstream and downsection order. Correlations of unknown 

tephra layers in the Willamette Valley to known tephras were determined from statistical comparison of chemical compositions, petrographic 

examination, and qualitative assessment of stratigraphic position. Some fluvial pumice accumulations consisted of multiple compositional modes, 

denoted as “major” and “minor” depending on relative abundance, which were analyzed separately. 14C yr BP, radiocarbon years before present; cm, 

centimeter; ka, thousand of years before present; m, meter; Ma, millions of years before present; mm, millimeter]

Sample

number

Location

Stratigraphic context

Correlative 

tephra layer 

(source area)

Age of tephra

(

14C yr BP 

except as 

noted)

Comments regarding 

stratigraphic relations and sources of 

Latitude Longitude age information

JEO 9/11/96-1(1) Cartney Park section

 44.3248N 123.2150W

Pumice clasts up to 3 cm 

diameter collected about 

1.8 m below modern surface from a thin and discontinuous horizon of 

pumice and airfall(?) 

tephra. Near base of 

Holocene overbank deposits thinly capping unit Qff2

Mazama

(Crater Lake)

6,73040 Hallett and others, 

1997

JEO 9/11/96-1(6) Silty airfall tephra collected 1.8 m below 

modern surface from a 

<0.5 cm discontinuous 

layer that has apparently 

been bioturbated and 

slightly reworked by surface processes. Sample was 

collected from a slightly 

thicker accumulation at the 

bottom of a paleoswale. 

About 0.75 m below horizon containing dispersed 

charcoal dated 5,860 

120 14C yr BP. Near 

base of Holocene overbank deposits thinly capping unit Qff2

Mazama

(Crater Lake)

6,73040 Hallett and others, 

1997
Appendixes 47

Sample

number

Location

Stratigraphic context

Correlative 

Tephra layer 

(source area)

Age of tephra

(

14C yr BP 

except as 

noted)

Comments regarding 

stratigraphic relations and sources of 

Latitude Longitude age information

JEO 9/11/96-1(9) Cartney Park section 

44.3248N 123.2150W

Pumice grains (up to 1 cm 

diameter) within cross-bedded fluvial sand 4.9 m 

below the modern surface 

in unit Qg2. Below paleosol and within Linn GravMajor Mode:

Wono (Crater 

Lake)

27,300300 Benson and others 

(1997) dated Wono and 

Trego Hot Springs ash 

layers at Pyramid 

Lake, Nevada

Minor Mode: <27,300300; Stratigraphically 

els unit as described by Summer Lake E >23,200300 between Wono and 

Allison (1953) at nearby 

Irish Bend locality

(unknown) Trego Hot Springs ash 

layers at Summer Lake 

(Davis,1985). Dates 

from Benson and others (1997)

JEO 9/11/96-1(10) Pumice grains (up to 

1 cm diameter) within 

cross-bedded fluvial

 sand 5.8 m below the modMajor Mode:

Wono (Crater 

Lake)

27,300300 Benson and others 

(1997)

Minor Mode: <27,300300: Stratigraphically 

ern surface (unit Qg2). Summer Lake E >23,200300 between Wono and 

Below paleosol and within 

Linn Gravels unit as 

described by Allison 

(1953) at nearby Irish Bend 

locality

(unknown) Trego Hot Springs 

ash layers at Summer 

Lake (Davis, 1985). 

Dates from Benson 

and others (1997)

WV-WF-2 Wheatland Ferry section

45.0845N 123.0662W

Pumice grains in fluvial 

sand collected about 

15 m below modern 

surface (above paleosol 

capping unit Qg2; below 

rhythmically bedded 

sand and silt of unit 

Qff2, within gray sands 

that likely correspond 

to the River Bend unit II 

of Glenn of 1965)

Tulelake tephra 

2,438 

(unknown)

<27,300300:

>23,200300

Stratigraphically 

between Wono and 

Trego Hot Springs

 ash layers at Tulelake 

(Rieck and others, 

1992). Dates from 

Benson and others 

(1997)

Table A2-1. Willamette Valley tephra and pumice correlations (Continued)

[Samples from sections exposed along Willamette River (shown in figure 10) are listed in downstream and downsection order. Correlations of unknown 

tephra layers in the Willamette Valley to known tephras were determined from statistical comparison of chemical compositions, petrographic 

examination, and qualitative assessment of stratigraphic position. Some fluvial pumice accumulations consisted of multiple compositional modes, 

denoted as “major” and “minor” depending on relative abundance, which were analyzed separately. 14C yr BP, radiocarbon years before present; cm, 

centimeter; ka, thousand of years before present; m, meter; Ma, millions of years before present; mm, millimeter]
48 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Table A2-1. Willamette Valley tephra and pumice correlations—Continued

[Samples from sections exposed along Willamette River (shown in figure 10) are listed in downstream and downsection order. Correlations of unknown 

tephra layers in the Willamette Valley to known tephras were determined from statistical comparison of chemical compositions, petrographic examination, 

and qualitative assessment of stratigraphic position. Some fluvial pumice accumulations consisted of multiple compositional modes, denoted as “major” and 

“minor” depending on relative abundance, which were analyzed separately. 14C yr BP, radiocarbon years before present; cm, centimeter; ka, thousand of 

years before present; m, meter; Ma, millions of years before present; mm, millimeter]

Sample

number

Location

Stratigraphic context

Correlative 

Tephra layer 

(source area)

Age of tephra

(

14C yr BP 

except as 

noted)

Comments regarding 

stratigraphic relations and sources of 

Latitude Longitude age information

JEO 9/19/96-2(2) Wheatland Ferry section

45.0845N 123.0662W

Pumice grains in crossbedded fluvial sand 

collected about 18 m below 

modern surface. Below 

paleosol and within unit 

Qg2, which is locally correlative to River Bend Unit 

I of Glenn (1965).

Major Mode:

Redcloud Pumice (Crater Lake)

<0.071 Ma 

(Ar40/Ar39)

Younger than 0.071 Ma 

Pumice Castle tephra 

(Bacon, 1983; C.R. 

Bacon, U.S. Geological Survey, oral commun. 1997); close 

association with Summer Lake E pumice at 

Wheatland Ferry may 

indicate Redcloud 

pumice is also 30–

23 ka

Minor Mode: <27,300300: Stratigraphically 

Summer Lake E >23,200300 between Wono and 

(unknown) Trego Hot Springs

ash layers at Summer 

Lake (Davis,1985). 

Dates from Benson 

and others (1997)

RBW-79-1848B River Bend section

45.1620N 123.0000W

Airfall silt ash collected 

about 16.5 m below modern surface. Described by 

Glenn (1965) and Richard 

Waitt (USGS, written commun., 1998). Near base of 

rhythmically bedded sand 

and silt of unit Qff2, and 

within transition zone of 

River Bend units II and III 

of Glenn (1965)

unknown unknown Sample collected by 

Richard Waitt, USGS. 

See description by 

Glenn (1965, p. 83–84)

RBW-79-1848A River Bend section

45.1620N 123.0000W

Pumice grains in fluvial 

sand collected about 19 m 

below modern surface. 

Above paleosol capping 

unit Qg2 and within bedded 

gray sands of River Bend 

unit II (Glenn, 1965)

Tulelake tephra 

2,438 

(unknown)

<27,300300:

>23,200300

Sample collected by 

Richard Waitt, USGS. 

Stratigraphically 

between Wono and 

Trego Hot Springs ash 

layers at Tulelake 

(Rieck and others, 

1992). Dates from 

Benson and others 

(1997)
Appendixes 49

Table A2-1. Willamette Valley tephra and pumice correlations—Continued

[Samples from sections exposed along Willamette River (shown in figure 10) are listed in downstream and downsection order. Correlations of unknown 

tephra layers in the Willamette Valley to known tephras were determined from statistical comparison of chemical compositions, petrographic examination, 

and qualitative assessment of stratigraphic position. Some fluvial pumice accumulations consisted of multiple compositional modes, denoted as “major” and 

“minor” depending on relative abundance, which were analyzed separately. 14C yr BP, radiocarbon years before present; cm, centimeter; ka, thousand of 

years before present; m, meter; Ma, millions of years before present; mm, millimeter]

Sample

number

Location

Stratigraphic context

Correlative 

Tephra layer 

(source area)

Age of tephra

(

14C yr BP 

except as 

noted)

Comments regarding 

stratigraphic relations and sources of 

Latitude Longitude age information

JEO-10/03/96-5(1) Weston Landing section

45.2007N 123.0453W

Pumice grains with diameters up to 4 mm in fluvial 

sand collected about 25 m 

below modern surface. 

Below paleosol capping 

Major Mode:

Trego Hot 

Springs (Crater 

Lake)

23,200300 Benson and others 

(1997)

Minor Mode: <27,300300: Stratigraphically 

unit Qg2, locally correla- Summer Lake E >23,200300 between Wono and 

tive with River Bend unit I 

of Glenn (1965)

(unknown) Trego Hot Springs ash 

layers at Summer Lake 

(Davis, 1985). Dates 

from Benson and others (1997)

JEO-10/09/96-2(1d) River Bend Sand and Gravel 

quarry, near Salem

44.8893N 122.9783W

Pumice clasts in 1 m thick 

lahar deposit, 12 m below 

modern surface within unit 

Qg2

Mount Jefferson 

Pumice

>0.04 Ma

(fission track 

age)

Correlative tephra 

exposed in southcentral Idaho underlies 

a Yellowstone tephra 

that has been dated by 

fission-track on glass 

at 0.0760.034 Ma

(1) (Pierce, 1985)
Table A2–2. Compositions of volcanic glass shards from deposits in the Willamette Valley (unshaded) and inferred 

correlative and dated tephra layers in the western United States (shaded)

[Values are given as oxides, in weight-percent, recalculated to 100 percent on a fluid-free basis. Replicates of a natural glass standard (RLS 132)

 provide indication of analytical precision. 14C yr BP, radiocarbon years before present; ka, thousands of years before the present; Ma, millions of years

before the present]

Sample SiO2 Al2O3 Fe2O3 MgO MnO CaO TiO2 Na2O K2O Wt%

Mazama Correlatives (6,730 40 14C yr BP)

JEO 9/11/96-1(1) 73.48 14.45 2.10 0.43 0.06 1.5 0.37 4.8 2.81 100.00

JEO 9/11/96-1(6) 73.38 14.44 2.23 .52 .05 1.62 .38 4.66 2.71 99.99

Mazama Ash average (n=100) 72.79 14.65 2.12 .46 .05 1.61 .42 5.19 2.71 100.00

Trego Hot Springs Ash Layer Correlatives (23,200 300 14C yr BP)

JEO 10/03/96-5(1) Major Mode 75.65 13.43 1.55 .19 .05 1.02 .18 4.52 3.41 100.00

LT-2

[Trego Hot Springs type location]

75.25 14.04 1.60 .21 .07 1.02 .24 4.28 3.29 100.00

92B-5.07

[Tephra in Pyramid Lake core 

dated 23,200±300 14C yr BP by 

Benson and others (1997)]

75.52 13.95 1.64 .21 .05 1.04 .22 4.05 3.32 100.00

Tulelake 1761

1Tulelake 176 is within the proper stratigraphic position in the Tulelake core to be the Trego Hot Springs ash bed (Rieck and others, 1992), and 

its chemical composition is more similar to some of the pumices sampled from the Willamette Valley than are the “type” Trego Hot Springs samples. We 

infer that all of these samples are from the Trego Hot Springs eruptive event, but that the pumices have slightly variable compositions.

75.44 13.62 1.53 .21 .06 1.02 .22 4.53 3.36 99.99

Summer Lake E Correlatives (<27,300 300; >23,200 300 14C yr BP)

JEO 9/11/96-1(9) Minor Mode 77.02 12.92 1.19 .15 .03 .81 .13 4.16 3.61 100.02

JEO 9/11/96-1(10) Minor Mode 76.84 13.03 1.22 .15 .05 .84 .16 4.14 3.57 100.00

JEO 9/19/96-2(2) Minor Mode 76.51 13.15 1.26 .14 .04 .82 .15 4.31 3.63 100.01

JEO 10/03/96-5(1) Minor Mode2

2JEO 10/03/96-5(1) (minor mode) is tentatively correlated with Summer Lake E, although it has significantly lower Fe and

Mg contents.

76.96 13.08 1.08 .11 .03 .79 .15 4.28 3.62 100.00

DR-82

[Summer Lake E]

76.65 13.14 1.25 .14 .05 .75 .18 4.21 3.61 99.98

Tulelake Ash Layer Correlatives (<27,300 300; >23,200 300 14C yr BP)

WV-WF-2 76.24 13.43 1.30 .17 .03 .90 .15 4.29 3.47 99.98

RBW-79-1848A(1) 76.16 13.32 1.36 .16 .02 .89 .16 4.33 3.60 100.00

RBW-79-1848A(2) 76.05 13.37 1.35 .15 .04 .88 .16 4.59 3.41 100.00

Tulelake 2438 76.76 12.97 1.33 .17 .04 .80 .20 4.22 3.52 100.01

Wono Ash Layer Correlatives (27,300300 14C yr BP)

JEO 9/11/96-1(9) Major Mode 74.50 13.86 1.93 .28 .04 1.30 .24 4.59 3.26 100.00

JEO 9/11/96-1(10) Major Mode 74.63 13.89 1.86 .26 .05 1.32 .22 4.56 3.2 99.99

NIXON-2 

(Wono type section)

74.54 13.81 2.10 .30 .06 1.34 .30 4.46 3.10 100.01

PL92B-7.85

[Tephra in Pyramid Lake core 

dated 27,300±300 14C yr BP by 

Benson and others (1997)]

74.34 13.98 1.96 .26 .05 1.26 .26 4.64 3.25 100.00

Redcloud Pumice Correlatives (<71 ka)

JEO 9/19/96-2(2) Major Mode 74.87 13.81 1.77 .24 .04 1.18 .24 4.51 3.35 100.01

CB-33 (Redcloud pumice) 74.60 13.94 1.76 .24 .03 1.13 .27 4.71 3.31 99.99

Mount Jefferson Pumice Correlatives (>40 ka)

JEO 10/09/96-2(2) 75.10 13.76 1.72 .32 .04 1.53 .24 4.74 2.54 99.99

SD 1490-1

[Pumice at Mount Jefferson]

74.85 14.08 1.79 .32 .05 1.54 .24 4.68 2.44 99.99

ARCO A2-8

[>0.040 Ma tephra in southcentral Idaho]

74.98 13.78 1.79 .31 .05 1.54 .26 4.77 2.52 100.00

Uncorrelated Samples

RBW-79-1848B 76.93 10.62 2.09 .19 .04 1.03 .21 5.80 3.38 99.99

Homogenous Glass Standard (18 electron microprobe analyses)

RLS 132

1

75.4

.1

11.3

.2

2.12

.04

.06

.01

.16

.01

.11

.01

.19

.01

4.9

.1

4.4

.1

100.00

50 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon
Appendixes 51

APPENDIX 3–14C age analyses

Radiocarbon age analyses were conducted for 17 organic carbon samples (charcoal, wood, and plant fragments) collected from outcrops within the study area. Beta Analytic Inc. performed the analyses using standard 

procedures. Sample locations, stratigraphic context, and results are summarized in table A3–1.

Table A3–1. Radiocarbon ages obtained during this study from map area

[All analyses performed by Beta Analytic Inc. For each location, ages displayed in downsection order. Longitude and latitude in decimal degrees; 14C yr BP, radiocarbon years before present; cm, centimeter; m, meter; mm, millimeter; %, percent]

Laboratory 

number

Location

Stratigraphic context Material analyzed

14C Date1

(

14 Latitude Longitude C yr BP)

Beta-98559 Wildish sand and gravel

44.1115N 123.0850W

Sandy silt about 10 cm below Qalc surface.Single wood fragment 9050

Beta-98558 Silty fine sand about 1.2 

surface.

m below Qalc Single wood fragment 5040

Beta-98725 Fluvial gravel about 1.2 m below Qalc 

surface.

Dispersed charcoal 52080

Beta-98562 Wildish sand and gravel

44.1093N 123.0745W

Wildish section

Sandy silt with abundant charcoal, wood fragments 1.0 m 

below Qalc surface.

Dispersed charcoal 

and wood fragments

Modern

(104.40.9%)2

Beta-98563 Sandy silt with isolated charcoal, 

wood, and cobbles, 2.1 m below 

Qalc surface.

Wood from 10 cm 

diameter log

6050

Beta-98560 Small lense of sand within sandy 

gravel about 4 m below Qalc surface.

Single wood fragment 3,70070 

Beta-98725 Cartney Park section

44.3248N 123.2150W

Disseminated 1- to 2-mm charcoal 

fragments (burned surface?) within 

clayey silt 1.04 m below surface 

mapped as unit Qff2, but locally 

capped by 1 to 2 m of Holocene overbank deposits of the Willamette River.

Dispersed charcoal 5,860120

Beta-98728 Bear Island

44.4730N 123.2148W

Sandy silt about 1.8 m below Qalc surface.Dispersed charcoal 230120

Beta-98729 Right bank Willamette River, river 

mile 138.4

44.4903N 123.2123W

Dispersed charcoal within paleosol 

about 6.9 m below surface mapped as 

Qff2. Sample could be younger wood 

or roots within Pleistocene paleosol, or 

alternatively, within a small area of 

younger deposits inset into the Pleistocene surface.

Dispersed charcoal 370100

Beta-98565 Left bank Willamette River, 

river mile 110.4

44.7250N 123.1502W

Silty fine sand 0.3 m below Qalc surface.Dispersed charcoal 26080

Beta-98730 Weakly developed paleosol in silty fine 

sand 3.7 m below Qalc surface.

Dispersed charcoal 2,55070

Beta-98564 Silty fine sand 3.8 m below Qalc surface.Dispersed charcoal 2,820100
52 Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon

Table A3-1. Radiocarbon ages obtained during this study from map area—Continued

Laboratory 

Number

Location

Stratigraphic Context Material Analyzed

14C Date3

(

14 Latitude Longitude C yr BP)

Beta-98724 Walling Sand and Gravel

44.8655N 122.9593W

Turner section

Sandy silt lenses within sandy, 

cobbly, gravel, about 1.5 m below 

slightly disturbed Qg1 surface.

10 cm diameter wood 

fragment with bark

12,17070

Beta-98555 Sand lenses within sandy, cobbly, 

gravel, about 1.0 m below slightly 

disturbed Qg1 surface.

Multiple wood fragments12,290110

Beta-98557 Sand lenses within sandy, cobbly, 

gravel, about 5.5 m below Qg1

surface.

Single wood fragment >46,930

Beta-98556 Sandy, cobbly, gravel, about 

6.5 m below Qg1 surface.

Single wood fragment 45,6403,200

Beta-99685 Wheatland Ferry section

45.0805 123.0662

Thin organic mat capping paleosol 

developed on unit Qg2 and below unit 

Qff2; about 16 m below Qff2 surface.

Fine organic detritus 22,060100

1. Conventional radiocarbon ages (in 14C yr BP) are based on the Libby half-life (5,568 yr) for 14C. The error stated is 1as judged by the analytical 

data alone. The age is referenced to A.D. 1950. 2. Carbon 14 content exceeds modern reference standard, indicating a post A.D. 1950 age. 3. Conventional radiocarbon ages (in 14C yr BP) are based on the Libby half-life (5,568 yr) for 14C. The error stated is 1as judged by the analytical 

data alone. The age is referenced to A.D. 1950.
Availability of Publications of the U.S. Geological Survey

Order U.S. Geological Survey (USGS) publications by calling 

the toll-free telephone number 1-888-ASK-USGS or contacting the offices listed below. Detailed ordering instructions, 

along with prices of the last offerings, are given in the current-year issues of the catalog "New Publications of the U.S. 

Geological Survey."

Books, Maps, and Other Publications

By Mail

Books, maps, and other publications are available by mail 

from—

USGS Information Services

Box 25286, Federal Center

Denver, CO 80225

Publications include Professional Papers, Bulletins, WaterSupply Papers, Techniques of Water-Resources Investigations, 

Circulars, Fact Sheets, publications of general interest, single 

copies of permanent USGS catalogs, and topographic and 

thematic maps.

Over the Counter

Books, maps, and other publications of the U.S. Geological 

Survey are available over the counter at the following USGS 

Earth Science Information Centers (ESIC's), all of which are 

authorized agents of the Superintendent of Documents:

• Anchorage, Alaska–Rm.101, 4230 University Dr.

• Denver, Colorado–Bldg. 810, Federal Center

• Menlo Park, California–Rm. 3128, Bldg. 3,

345 Middlefield Rd.

• Reston, Virginia–Rm. 1 C402, USGS National Center,

12201 Sunrise Valley Dr.

• Salt Lake City, Utah–2222 West, 2300 South

• Spokane, Washington–Rm.135, U.S. Post Office

Building, 904 West Riverside Ave.

• Washington, D.C.–Rm. 2650, Main Interior Bldg.,

18th and C Sts., NW.

Maps only may be purchased over the counter at the following 

USGS office:

• Rolla, Missouri–1400 Independence Rd.

Electronically

Some USGS publications, including the catalog "New Publications of the U.S. Geological Survey" are also available electronically on the USGS's World Wide Web home page at 

http://www.usgs.gov

Preliminary Determination of Epicenters

Subscriptions to the periodical "Preliminary Determination of 

Epicenters" can be obtained only from the Superintendent of 

Documents. Check or money order must be payable to the 

Superintendent of Documents. Order by mail from—

Superintendent of Documents

Government Printing Office

Washington, DC 20402

Information Periodicals

Many Information Periodicals products are available through 

the systems or formats listed below:

Printed Products

Printed copies of the Minerals Yearbook and the Mineral Commodity Summaries can be ordered from the Superintendent of 

Documents, Government Printing Office (address above).

Printed copies of Metal Industry Indicators and Mineral Industry Surveys can be ordered from the Center for Disease Control 

and Prevention, National Institute for Occupational Safety and 

Health, Pittsburgh Research Center, P.O. Box 18070, Pittsburgh, PA 15236–0070.

Mines FaxBack: Return fax service

1. Use the touch-tone handset attached to your fax machine's 

telephone jack. (ISDN [digital] telephones cannot be used 

with fax machines.)

2. Dial (703) 648-4999.

3. Listen to the menu options and punch in the number of your 

selection, using the touch-tone telephone.

4. After completing your selection, press the start button on 

your fax machine.

CD-ROM

A disc containing chapters of the Minerals Yearbook (1993– 

95), the Mineral Commodity Summaries (1995–97), a statistical compendium (1970–90), and other publications is updated 

three times a year and sold by the Superintendent of Documents, Government Printing Office (address above).

World Wide Web

Minerals information is available electronically at 

http://minerals.er.usgs.gov/minerals/

Subscription to the catalog "New Publications of the U.S.

Geological Survey"

Those wishing to be placed on a free subscription list for the 

catalog "New Publications of the U.S. Geological Survey" 

should write to—

U.S. Geological Survey

903 National Center

Reston, VA 20192
Selected Series of U.S. Geological Survey Publications

Books and Other Publications

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS 

investigations and research.

Bulletins contain significant data and interpretations that are 

of lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers.

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of 

wide interest to professional geologists, hydrologists, and engineers. The series covers investigations in all phases of hydrology, including hydrogeology, availability of water, quality of 

water, and use of water.

Circulars are reports of programmatic or scientific information of an ephemeral nature; many present important scientific 

information of wide popular interest. Circulars are distributed 

at no cost to the public.

Fact Sheets communicate a wide variety of timely information 

on USGS programs, projects, and research. They commonly 

address issues of public interest. Fact Sheets generally are two 

or four pages long and are distributed at no cost to the public.

Reports in the Digital Data Series (DDS) distribute large 

amounts of data through digital media, including compact 

disc-read-only memory (CD-ROM). They are high-quality, 

interpretive publications designed as self-contained packages 

for viewing and interpreting data and typically contain data 

sets, software to view the data, and explanatory text.

Water-Resources Investigations Reports are papers of an

interpretive nature made available to the public outside the formal USGS publications series. Copies are produced on request 

(unlike formal USGS publications) and are also available for 

public inspection at depositories indicated in USGS catalogs.

Open-File Reports can consist of basic data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories.

Maps

Geologic Quadrangle Maps (GQ's) are multicolor geologic 

maps on topographic bases in 7.5 or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, 

surficial, or engineering geology. Maps generally include brief 

texts; some maps include structure and columnar sections only.

Geophysical Investigations Maps (GP's) are on topographic 

or planimetric bases at various scales. They show results of 

geophysical investigations using gravity, magnetic, seismic, or 

radioactivity surveys, which provide data on subsurface structures that are of economic or geologic significance.

Miscellaneous Investigations Series Maps or Geologic 

Investigations Series (I's) are on planimetric or topographic 

bases at various scales; they present a wide variety of format 

and subject matter. The series also includes 7.5-minute quadrangle photogeologic maps on planimetric bases and planetary 

maps.

Information Periodicals

Metal Industry Indicators (MII's) is a free monthly newsletter that analyzes and forecasts the economic health of five 

metal industries with composite leading and coincident 

indexes: primary metals, steel, copper, primary and secondary 

aluminum, and aluminum mill products.

Mineral Industry Surveys (MIS's) are free periodic statistical and economic reports designed to provide timely statistical 

data on production, distribution, stocks, and consumption of 

significant mineral commodities. The surveys are issued 

monthly, quarterly, annually, or at other regular intervals, 

depending on the need for current data. The MIS's are published by commodity as well as by State. A series of international MIS's is also available.

Published on an annual basis, Mineral Commodity Summaries is the earliest Government publication to furnish estimates 

covering nonlife mineral industry data. Data sheets contain 

information on the domestic industry structure, Government 

programs, tariffs, and 5-year salient statistics for more than 90 

individual minerals and materials.

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in interpreting that performance. The Minerals Yearbook consists of 

three volumes. Volume I, Metals and Minerals, contains chapters about virtually all metallic and industrial mineral commodities important to the United States economy. Volume II, 

Area Reports: Domestic, contains a chapter on the minerals 

industry of each of the 50 States and Puerto Rico and the 

Administered Islands. Volume III, Area Reports: International, 

is published as four separate reports. These reports collectively 

contain the latest available mineral data on more than 190 foreign countries and discuss the importance of minerals to the 

economies of these nations and the United States.

Permanent Catalogs

"Publications of the U.S. Geological Survey, 1879–1961" 

and "Publications of the U.S. Geological Survey, 1962–

1970" are available in paperback book form and as a set of 

microfiche.

"Publications of the U.S. Geological Survey, 1971–1981" is 

available in paperback book form (two volumes, publications 

listing and index) and as a set of microfiche. 

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.

O’Connor and others—Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon—U.S. Geological Survey Professional Paper 1620