Prepared in cooperation with King County, Washington

Geologic Map of the Vashon 7.5' Quadrangle and Selected 

Areas, King County, Washington

By Derek B. Booth, Kathy Goetz Troost, and Rowland W. Tabor

Pamphlet to accompany

Scientific Investigations Map 3328

2015

U.S. Department of the Interior

U.S. Geological Survey
ii

Contents

Introduction ..................................................................................................................................................................... 1

Acknowledgments ........................................................................................................................................................... 1

Previous Mapping ........................................................................................................................................................... 1

Geologic Setting.............................................................................................................................................................. 2

Stratigraphic Relations and Nomenclature...................................................................................................................... 2

Structure.......................................................................................................................................................................... 5

Description of Map Units ................................................................................................................................................. 5

Postglacial Deposits .................................................................................................................................................... 5

Younger Glacial Deposits............................................................................................................................................ 6

Older Glacial and Nonglacial Deposits........................................................................................................................ 7

References Cited ............................................................................................................................................................ 8

Figures

Figure 1. Comparison of the marine oxygen-isotope curve (MIS, marine isotope stage) using the deep-sea 

oxygen-isotope data from core ODP 677 from Shackleton and others (1990), global magnetic polarity 

curve (Mankinen and Dalrymple, 1979; Barendregt, 1995; Cande and Kent, 1995), and ages of climatic 

intervals in the Puget and Fraser Lowlands. . ............................................................................................. 3

Tables

Table 1. IRSL (infrared stimulated luminescence) data for sites in the Vashon 7.5' quadrangle, Washington. .......... 4

Table 2. Paleomagnetic data for sites in the Vashon 7.5' quadrangle, Washington. .................................................. 4
1

Introduction

This map is an interpretation of a 6-ft-resolution lidar-derived digital elevation model combined 

with geology by Derek B. Booth and Kathy Goetz Troost. Field work by Booth and Troost was located 

on the 1:24,000-scale topographic map of the Vashon and Des Moines 7.5' quadrangles that were 

published in 1997 and 1995, respectively. Much of the geology was interpreted from landforms 

portrayed on the topographic maps, supplemented by field exposures, where available. In 2001, the 

Puget Sound Lidar Consortium (see http://pugetsoundlidar.org/) obtained a lidar-derived digital 

elevation model (DEM) for Vashon Island and the Des Moines quadrangle. For a brief description of 

lidar and this data acquisition program, see Haugerud and others (2003). This new DEM has a horizontal 

resolution of 6 ft (1.83 m) and mean vertical accuracy of about 1 ft (about 0.3 m). The greater resolution 

and accuracy of the lidar DEM facilitated a much-improved interpretation of many aspects of the 

surficial geology, especially the distribution and relative age of landforms and the materials inferred to 

comprise them. Booth and Troost were joined by Tabor to interpret the new lidar DEM but have done no 

futher field work for this map.

This map, the Vashon quadrangle and selected adjacent areas, encompasses most of Vashon 

Island, Maury Island, and Three Tree Point in the south-central Puget Sound. One small area in the 

Vashon quadrangle on the east side of Puget Sound is excluded from this map but included on the 

adjacent Seattle quadrangle (Booth and others, 2005). The map displays a wide variety of surficial 

geologic deposits, which reflect many geologic environments and processes. Multiple ice-sheet 

glaciations and intervening nonglacial intervals have constructed a complexly layered sequence of 

deposits that underlie both islands to a depth of more than 300 m below sea level. These deposits not 

only record glacial and nonglacial history but also control the flow and availability of ground water, 

determine the susceptibility of the slopes to landslides, and provide economic reserves of sand and 

gravel. The islands are surrounded by channels of Puget Sound, some as deep as the islands are high 

(>600 ft (~200 m)). The shorelines provide many kilometers of well-exposed coastal outcrops that 

reveal abundant lithologic and stratigraphic details not ordinarily displayed in the heavily vegetated 

Puget Lowland.

Acknowledgments

We thank Russ Evarts and David Frank for review of an earlier version of this map. Ralph 

Haugerud helped interpret parts of the lidar DEM. This second version has improvements thanks to 

further reviews by Russ Evarts and Greg Wessel.

Previous Mapping

The geology of the Vashon quadrangle was first mapped by Willis (1898), who named the most 

recent glaciation after deposits he observed on Vashon Island. Subsequent work includes the regional 

mapping of Garling and others (1965) and a nearshore study by the Washington Department of Ecology 

(1979). This edition of the Vashon 7.5' quadrangle follows prior mapping by Booth (1991), conducted in 

1987, 1988, and 1989 as part of a King County-supported groundwater study. Since that time, a wealth 

of new geologic data has become available through the digital compilation of geotechnical explorations 

and water-well logs. Additional fieldwork between 1996 and 2004 has emphasized reinterpretation of 

the stratigraphy along the coastal bluffs, supported by luminescence dating (Mahan and others, 2003; 

table 1) and paleomagnetic investigations (Hagstrum and others, 2002; table 2), together with careful 

reevaluation of stratigraphic relations in the surrounding area, particularly in the Gig Harbor and 

Tacoma North quadrangles immediately to the south and southwest (Troost, K.G., Booth, D.B., Borden, 

R., and Wells, R., unpub. field maps, 1994–2001).
2

Geologic Setting

During the Pleistocene, the Puget Lowland was glaciated several times by ice originating in the 

mountains of British Columbia (Crandell and others, 1958; Easterbrook and others, 1967). By analogy 

to the most recent glaciation, a lobe of the Cordilleran ice sheet (named the ”Puget lobe” by Bretz, 1913) 

advanced down the trough now occupied by Puget Sound, filling the lowland from the Cascade Range to 

the Olympic Mountains. During glacial times, lithologically distinctive clasts, particularly high grade 

metamorphic rocks, were carried southward by ice and meltwater and were subsequently deposited in 

the Puget Lowland. These exotic lithologies are now found in tills (typically impermeable and laid down 

beneath the ice sheet itself) and in glacial outwash (permeable sand and gravel deposits laid down by 

water originating from the ice sheet). During intervening nonglacial times, drainage from the mountains 

surrounding the Puget Lowland transported a more limited suite of rock types, particularly 

unmetamorphosed sandstones and lavas. In the Vashon quadrangle, however, many of the nonglacially 

transported sedimentary clasts are reworked from lowland glacial deposits, so nonglacial deposits also 

include exotic lithologies.

The existing channels of Puget Sound currently isolate the islands from the mainland sediment 

supply, so sediments being deposited here today do not display the local, nonglacial lithologies derived 

from the adjacent Olympic Mountains and Cascade Range. Yet the widespread presence of this material 

in older deposits on both Vashon and Maury Islands suggests that the present channel configuration did 

not necessarily exist before the most recent glaciation. Nonglacial deposits in the map area, therefore,

form a discontinuous, incomplete record of lowland drainage courses, and they are interbedded with the 

(also discontinuous) deposits that record regional glacial advances.

Stratigraphic Relations and Nomenclature

The naming and regional correlation of the individual glacial advances in the Puget Lowland has 

a long and still-evolving history. Willis (1898) first presented evidence for multiple episodes of 

glaciation in the Puget Lowland. Crandell and others (1958) proposed a sequence of four glaciations 

separated by nonglacial intervals based on stratigraphic sequences in the southern Puget Lowland, about 

20 km southeast of Vashon and Maury Islands. Easterbrook and others (1967) named and described 

deposits north of the map area, assigning them to three glaciations and their intervening interglacial 

periods. The earliest efforts to date these separated stratigraphic sequences (Easterbrook and others, 

1981; Easterbrook, 1982) did not provide demonstrable correlations beyond the most recent ice-sheet 

advance. Further work by Westgate and others (1987) also found no correlation between these northern 

and southern sequences except for that of the most recent glacial advance, the Vashon stade of the Fraser 

glaciation, which reached a maximum about 14,000 14C yr B.P. (or about 17,000 calendar years ago) 

(Porter and Swanson, 1998).
3

Figure 1. Comparison of the marine oxygen-isotope curve (MIS, marine isotope stage) using the deep-sea 

oxygen-isotope data from core ODP 677 from Shackleton and others (1990), global magnetic polarity curve 

(Mankinen and Dalrymple, 1979; Barendregt, 1995; Cande and Kent, 1995), and ages of climatic intervals in 

the Puget and Fraser Lowlands. Ages for deposits of the Possession glaciation through Double Bluff glaciation 

are from Easterbrook and others (1981), Easterbrook (1986), Blunt and others (1987), and Easterbrook (1994); 

ages for older units are from Troost and others (2003, 2005). Ages for the Olympia nonglacial interval are from 

Armstrong and others (1965), Mullineaux and others (1965), Pessl and others (1989), and Troost (1999). Ages 

for the Coquitlam stade are from Hicock and Armstrong (1985); ages for the Port Moody interstade are from 

Hicock and Armstrong (1981). Ages for the Vashon stade are from Armstrong and others (1965) and Porter and 

Swanson (1998). Ages for the Everson interstade are from Dethier and others (1995) and Kovanen and 

Easterbrook (2001). Ages for the Sumas stade are from Clague and others (1997), Kovanen and Easterbrook 

(2001), and Kovanen (2002). Modified from Booth and others (2004a).

On this map, deposits of pre-Fraser glaciation age (see fig. 1) are assigned specific 

lithostratigraphic names, if they can be traced laterally from localities with luminescent dates (Mahan 

and others, 2003) that correspond to formally or informally defined deposits. These correlations are 

supported by paleomagnetic measurements (Hagstrum and others, 2002, table 1) that locally permit

correlation of widely separated deposits by virtue of unusual pole directions. These determinations, in 

combination with extensive subsurface data and concurrent mapping of the adjacent quadrangles to the 

south and west, permit the recognition and naming of deposits in the quadrangle as old as marine isotope Matuyama Brunhes

Geologic

age

Chron/

subchron

Polarity

(black =

normal)

Age

( ka)

δ18O 

( ‰) Lowland climatic intervals

0 -1 -2 -3 0

200

300

400

100

500

600

700

800

900

1000

Fraser glaciation (30-10 ka)

 Olympia nonglacial interval (60-15 ka)

 Unnamed glaciation (Hamm Creek beds)

 (215-190 ka)

De!ance glaciation (280-215 ka)

Sumas stade (11.5-10 ka)

 Everson interstade (13-11.5 ka)

Vashon stade (15-13 ka)

 Lawton Clay

 Esperance Sand (Advance outwash)

 Vashon till

Port Moody interstade (23-21 ka)

Coquitiam stade (30-25 ka)

Unamed glacial and interglacial intervals

Whidbey interglaciation (125-80 ka)

Double Blu" glaciation (190-125 ka)

Possesion glaciation (80-60 ka)

Laschamp

Blake

Biwa I/Jamaica

Biwa III

Emperor

Big Lost

Delta

Biwa II/Levantine
4

stage 8 (MIS 8; see also Booth and others, 2004a). Deposits in the map area include all of the named 

glacial and nonglacial intervals that Easterbrook and others (1967) identified on Whidbey Island, 30 km 

to the north.

Table 1. IRSL (infrared stimulated luminescence) data for sites in the Vashon 7.5' quadrangle, Washington.

[Dates from S. Mahan., U.S. Geological Survey. Denver, CO, and Mahan and others, 2003. Samples collected in 2002. Ages 

reflect average of 10-minute bleach (minimum age) and 60-minute bleach (maximum age) using CS-3-67 orange filter]

Site and 

lab No. Site name Location(GPS NAD27)

Location on

lidar base

(NAD83)

Elevation

feet (meters) Material

Average

IRSL age

(yrs)

Unit

label

WA-28 Wingehaven 47.4979 N 47.4975 N

Park 122.4592 W 122.4602 W

60 (19.7) Silt 400,000 Qrm

WA-29 Wingehaven 47.49783 N 47.49783 N

Park 122.45771 W 122.4591 W

5 (1.6) Silt 400,000 Qrm

In addition, deposits at several localities exposed along the east shore of Vashon Island from 

Klahanie north to Dolphin Point exhibit reversed polarity, indicating they are of even greater antiquity 

than those in table 1, (>774 ka). Although these reversely polarized deposits could have been deposited

during the Blake reversal at about 130 ka, their exposure at the core of an anticline associated with 

crustal deformation south of the Seattle Fault (Booth and others, 2004b) and their isolation from younger 

deposits lead us to interpret them as older, Matuyama-age deposits.

Table 2. Paleomagnetic data for sites in the Vashon 7.5' quadrangle, Washington.

Site 

No. Lab No. Site name Location (GPS NAD27)1

Location on lidar 

base (NAD83)

Approximate 

elevation in 

feet (meters) 

[feet2]

Polarity Unit label

N37 T0145 Winghaven Park 47.497 N 47.4977 N

122.463 W 122.4642 W

73 (24) [221] Normal Qva

R18 T0142 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

0 [8] Reversed Qrm

T9 T9046 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

0 [8] Transitional Qrm

T12 T0133 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

3 (1) [8] Transitional Qrm

T14 T1309 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

3 (1) [8] Transitional Qrm

T15 T1312 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

3 (1) [8] Transitional Qrm

T16 T1315 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

2 (0.66) [8] Transitional Qrm

T17 T1318 Winghaven Park 47.497 N 47.4977 N

122.457 W 122.4590 W

0 [8] Transitional Qrm

N36 T0139 Sylvan Beach 47.501 N 47.4983 N.

122.477 W 122.5012 W

0 [3.6] Normal Qva

1

 Hagstrum and others (2002, table 1). 2

 Lidar elevation, in feet, at DB station site location.

Deposits of Vashon age are widely distributed and dated throughout the lowland region. They

are well exposed on Vashon and Maury Islands and are so named here. In contrast, the Colvos Sand 
5

Member (Walters and Kimmel, 1968) of the Vashon Drift (equivalent to the Colvos Sand of Garling and 

others, 1965), described as the lowermost member of the advance outwash deposits of the Vashon-age 

ice sheet, has been abandoned as a lithostratigraphic unit because it lacks both lithologic or textural 

distinction and stratigraphic significance (Booth, 1991). This follows convention in geologic mapping 

throughout the central Puget Lowland for the past 20 years (for example, Minard, 1983; Pessl and 

others, 1989). We reassigned these strata to the Vashon advance outwash (Qva).

The Kitsap Formation (Armstrong and others, 1965; see also Garling and others, 1965) is also 

abandoned, following recent usage elsewhere in the region (see, for example, Booth and Troost, 2005; 

Troost and others, 2005). Its utility as a stratigraphic marker is hampered, in part, by the formation’s 

definition as fine-grained sediments lying between two other units of uncertain value, the Salmon 

Springs Drift and herein-abandoned Colvos Sand Member. The formation as defined may also be 

substantially time-transgressive, possibly spanning more than one glaciation. For example, Garling and 

others (1965, p. 31) suggest that it may be correlative with any of several other units: the 15,000-yearold Lawton Clay Member of the Vashon Drift (Mullineaux and others, 1965); the Quadra Sand of 

Clague (1976), identified as advance outwash of the Vashon-age ice advance; interglacial deposits of 

finite radiocarbon (for example, Olympia) age in the Seattle area (Stark and Mullineaux, 1950); or 

deposits of the Whidbey Formation, which predate even the Possession glaciation of Easterbrook and 

others (1967). Deeter (1979) mapped the Kitsap Formation northwest of Vashon Island but also noted 

ambiguities in its definition and usage. Abandonment of this unit follows recent regional stratigraphic 

convention (for example, Blunt and others, 1987). We reassign its strata to either the earliest deposit of 

the Vashon-age glacial advance (Qvlc) or to pre-Fraser-age deposits.

Landslide and related deposits make up most of the post-Vashon-age deposits in the map area. 

Of particular interest is the large block slide of the Dilworth area. Although shown as a coherent block 

on the map, subsidiary block displacements are common along the Glen Acres-Dilworth road (Gres 

Wessel, written commun., 2013). Concentric arcuate scarps on the southwest side of the Burton 

Peninsula suggest a block slide, but without evidence of unit offset or other morphological change in the 

down-dropped blocks, this slide is less certain.

Structure

The eastern tip of Maury Island is cut by a strong northeast-trending lineament revealed by lidar 

that we interpret to be a fault with the east side dropped down. The fault cuts pre-Vashon-age units 

(Qpff and Qpdt) and offsets a Holocene and Pleistocene landslide (Qols). It is buried by a younger, 

probably Holocene, landslide. The lineament (fault) definitely cuts the ice-grooved pavement, indicating 

post-ice-advance movement. The older landslide does not have the smoothed morphology characteristic 

of sublacustrine landslides, indicating the latest fault movement is older than glacial Lake Bretz age or 

about 16,000 calendar years ago (R.A. Haugerud, written commun, 2011).

DESCRIPTION OF MAP UNITS

[MIS, marine isotope stage]

POSTGLACIAL DEPOSITS

m Modified land (Holocene)—Gravel, sand, silt, and other materials of substantial areal extent 

or thickness placed or modified as a direct result of human activity, including 

extensively graded natural deposits. Mapped where borehole data provide sufficient 

information to delineate extent and where greater than about 2 m in thickness, or 
6

where topography and overlying development suggests likelihood of fill. Thin 

deposits of fill are present throughout map area but are not mapped due to lack of 

information. Loose to weakly consolidated. Extensive areas of unit Qva on Maury 

Island shown as modified land

hs Hard surface (Holocene)—Mostly continuous hard surface, includes major roads, parking 

lots, and large building. Includes minor landscaped areas

Qls Landslide deposits (Holocene)—Diamicts composed of broken to internally coherent 

surficial deposits derived from upslope

Qols Old landslide deposits (Holocene and Pleistocene)—Diamict similar to Qls, but 

morphology less distinct and (or) significantly eroded. Queried where uncertain

Qlsq Landslide deposits, questionable (Holocene)—Materials similar to Qls, but some features 

determined from lidar DEM, such as concave head scarp and irregular morphology, 

indistinct or lacking

Qmw Mass-wasting deposits (Holocene)—Colluvium, soil, or landslide debris with indistinct 

morphology, mapped where sufficiently continuous and thick enough to obscure 

underlying deposits. Many deposits mapped from lidar DEM, mainly on the northern 

end of Vashon Island in gullies. Gradational contacts with units Qa, Qf, and Qls

Qw Wetland deposits (Holocene)—Peat and fine-grained(?) alluvium; poorly drained and 

intermittently wet. Compiled from King County (1983). Grades into unit Qa

Qbtf Beach deposits and tidal flats (Holocene)—Sand, pebbles, and shells deposited or 

reworked by wave action; locally well sorted. Grades at stream mouths into unit Qa. 

Tidal flats deposits are silt, sand, and organic sediment and detritus. Loose to 

weakly(?) consolidated

Qbo Beach deposits, old (Holocene)—Mapped north of Cedarhurst near Burton, at Three Tree 

Point, and at Point Robinson on Maury Island. Terraces bearing such deposits are 

about 10–12 ft (3–4 m) above sea level but are commonly covered by artificial fill 

(m). Equivalent deposits may be present elsewhere but are obscured by development

Qf Fan deposits (Holocene)—Boulders, cobbles, and sand forming poorly sorted(?) lobate 

deposits where streams emerge from confining valleys and reduced gradients cause 

some of the sediment loads to be deposited. Gradational with unit Qa

Qfo Fan deposits, old (Holocene)—Materials similar to Qf, but partially eroded. Commonly 

separated from other valley deposits by low scarp. Many modified by man

Qa Alluvium (Holocene)—Moderately sorted deposits of cobble gravel, pebbly sand, and sandy 

silt along rivers and streams. Also includes alluvial fans, common particularly where 

streams reach the coastline. Surfaces generally unvegetated. Grades into units Qf, 

Qw, and Qbtf

Qoa Older alluvium (Holocene and Pleistocene)—Texturally equivalent to unit Qa but deposits 

lie at higher altitudes and typically have greater relief than the younger alluvium. 

Some form terraces above modern valleys, especially along Judd and Shake Mill 

Creeks. May locally include deposits of late Fraser-age glaciation that cannot be 

unequivocally assigned a pre-Holocene origin

YOUNGER GLACIAL DEPOSITS

Deposits of Vashon stade of Fraser glaciation of Armstrong and others (1965) 

(Pleistocene)

Qvr Recessional outwash deposits—Stratified sand and gravel, moderately to well sorted, 

with less common silty sand and rare silty clay. Mantles the upland till surface; 

accumulated predominantly as outwash plains and valley trains
7

Qvrc Outwash channels and deposits—Deposits in channels mostly crosscutting regional 

glacial grooves, determined from lidar DEM. Probable subglacial origin. Channel fills 

may not contain outwash deposits, but all channels and deposits probably mantled by 

Holocene deposits. Smaller channels not mapped

Qvrl Recessional lacustrine deposits—Laminated silt and fine sand, deposited in 

proglacial lakes. Parentheses around label on map indicate unit preserved in block 

slide

Qvrls Sublacustrine landslide deposits—Mostly deposited under glacial Lake Russell, but 

slides below ~250 ft (~ 76 m) elevation may have been deposited under glacial Lake 

Bretz. Mapped from lidar DEM on basis of elevation and subdued, fluid appearance. 

May include some subaerial landslides (Qls)

Qvi Ice-contact deposits—Similar in texture to unit Qvr, but containing collapse features and 

rare till lenses that suggest deposition near stagnant or active glacial ice. In lidar 

DEM, characterized by relatively rough topography and many complex channels 

Qvt Till—Mainly compact diamict with subangular to rounded clasts, glacially transported 

and deposited. Unit is typically at most a few tens of meters thick and deposited as an 

undulating layer that has over 100 m of relief across the islands. Contact with unit 

Qvr is gradational where mantled by outwash. Parentheses around label on map

indicate unit preserved in block slide

Qva Advance outwash deposits—Well-bedded sandy gravel to more common medium- and 

fine-grained sand, generally firm and unoxidized; deposited by proglacial streams. 

Tends to grade downward from gravelly sand to uniform medium-fine sand; unit 

includes, in part, the Colvos Sand of Garling and others (1965) and is correlative with 

the Esperance Sand Member of the Vashon Drift (Mullineaux and others, 1965). Base 

of unit is placed at either uppermost appearance of silt or clay (assigned to unit Qvlc

or pre-Fraser deposits) or an abrupt transition to more oxidized clasts of typically 

nonglacial origin. Parentheses around label on map indicate unit preserved in block 

slide

Qvlc Lawton Clay Member of the Vashon Drift—Stiff to hard, laminated to massive silt, 

clayey silt, and silty clay deposited in lowland or proglacial lakes. Marks transition 

from nonglacial to earliest glacial time, although unequivocal evidence for glacial or 

nonglacial origin may be absent. Deposits of similar age and texture are included in 

unit Qpff where evidence of age and (or) depositional environment is absent

OLDER GLACIAL AND NONGLACIAL DEPOSITS

Qpf Deposits of pre-Fraser glaciation age (Pleistocene)—Massive to laminated silt and clay, 

and variably oxidized bedded sand and gravel. May locally include deposits (Qpon, 

Qponf) predating the Olympia nonglacial interval of Mullineaux and others (1965),

where exposures are inadequate to identify at map scale

Qpfc Coarse-grained facies—Predominantly sand and gravel, fluvially deposited

Qpff Fine-grained facies—Predominantly silt and clay, deposited in lakes or marine

environments. Parentheses around label on map indicate unit preserved in block slide

Qpof Pre-Olympia deposits, fine-grained (Pleistocene)—Predominantly silt and clay, deposited 

in lakes or marine environments. Very dense and hard

Qpog Glacial deposits of pre-Olympia age (Pleistocene)—Weakly to strongly oxidized silt, sand, 

gravel, and local till of glacial origin. Underlies Vashon-age deposits and thus must 

also be of pre-Olympia age. Sediment is of inferred glacial origin, based on presence 

of clasts requiring southward ice-sheet transport
8

Qpogt Till—Predominantly till or other diamict where thick enough to show at map scale

Qpogc Coarse-grained facies—Predominantly gravel and sand. Located on western edge of 

quadrangle, where it is continuous with more extensive exposures in the Olalla 7.5' 

quadrangle

Qpogf Fine-grained facies—Predominantly silt and clay, deposited in lakes or marine

environments

Qpon Nonglacial deposits of pre-Olympia age (Pleistocene)—Sand, silt (locally organic rich), 

gravel, and peat, discontinuously and thinly interbedded. Generally very dense and 

hard

Qponf Fine-grained facies—Predominantly silt and clay, deposited in lakes or marine

environments

Possession Drift of Easterbrook and others (1967) (Pleistocene)—Weakly to strongly 

oxidized silt, sand, and gravel of glacial origin, including lacustrine and ice-contact 

deposits, outwash, and till. Identified only where absolute age control or dated 

stratigraphic position provides stratigraphic control; therefore, Possession-age 

deposits are likely more extensive than mapped. Correlative with MIS 4, with ages

from approximately 80 to 70 ka. Very dense and hard

Qpdt Till—Predominantly till or other diamict where thick enough to show at map scale

Qpdc Coarse-grained facies—Predominantly sand and gravel, fluvially deposited

Qpdf Fine-grained facies—Predominantly silt and clay, deposited in lakes or marine

environments

Qwb Whidbey Formation (Pleistocene)—Interbedded clay, silt, sand, and gravel layers; locally 

includes abundant organic material, paleosols, peat, tephra, and pumice-rich layers. 

Deposited by lowland streams or in floodplain environments during the nonglacial 

period prior to the Possession glaciation. Correlative with MIS 5, from 125 to 80 ka. 

Mapped only where absolute age control is available; therefore, Whidbey Formation 

deposits are likely more extensive than mapped. Very dense and hard

Qwbc Coarse-grained facies—Predominantly sand and gravel, fluvially deposited

Qrm Reversely magnetized deposits (Pleistocene)—Interbedded silt and sand. Reversely 

magnetized and thus presumably more than 774,000 years old; optical ages from 

samples WA-28 and WA-29 (Mahan and others, 2003; table 1) are indeterminate but 

likely >400,000 years old

References Cited

Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, J.B., 1965, Late Pleistocene stratigraphy 

and chronology in southwestern British Columbia and northwestern Washington: Geological Society 

of America Bulletin, v. 76, p. 321–330.

Barendregt, R.W., 1995, Paleomagnetic dating methods, in Rutter, N.W., and Catto, N.R., eds., Dating 

methods for Quaternary deposits: Geological Association of Canada, GEOtext2, 308 p.

Blunt, D.J., Easterbrook, D.J., and Rutter, N.W., 1987, Chronology of Pleistocene sediments in the 

Puget Lowland, Washington: Washington Division of Geology and Earth Resources, Bulletin 77, p. 

321–349.

Booth, D.B., 1991, Geologic map of Vashon and Maury Islands, King County, Washington: U.S. 

Geological Survey Miscellaneous Field Studies Map MF–2161, scale 1:24:000.

Booth, D.B., and Troost, K.G, 2005, Geologic map of the Olalla 7.5-minute quadrangle, Washington: 

U.S. Geological Survey Scientific Investigations Map 2902, scale 1:24,000.
9

Booth, D.B., Troost, K.G., Clague, J.J., and Waitt, R.B., 2004a, The Cordilleran ice sheet—Chapter 2, in

Gillespie, A., Porter, S.C., and Atwater, B., eds., The Quaternary period in the United States: 

International Union for Quaternary Research, Elsevier Press, p. 17–43.

Booth, D.B., Troost, K.G., and Hagstrum, J.T., 2004b, Deformation of Quaternary strata and its 

relationship to crustal folds and faults, central Puget Lowland, Washington: Geology, v. 32, p. 505–

508.

Booth, D.B., Troost, K.G., and Shimel, S.A., 2005, Geologic map of northwestern Seattle (part of the 

Seattle North 7.5' x 15' quadrangle), King County, Washington: U.S. Geological Survey Scientific 

Investigations Map 2903, scale 1:12,000.

Bretz, J H., 1913, Glaciation of the Puget Sound region: Washington Geological Survey Bulletin, no. 8, 

244 p.

Cande, S.C., and Kent, D.V. 1995, Revised calibration of the geomagnetic polarity timescale for the 

Late Cretaceous and Cenozoic: Journal of Geophysical Research, Solid Earth, v. 100, no. B4, p. 6093–

6095.

Clague, J.J., 1976, Quadra Sand and its relation to the late Wisconsin glaciation of southwest British 

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