122°0'0"W

122°0'0"W

122°2'30"W

122°2'30"W

122°5'0"W

122°5'0"W

47°35'0"N

47°35'0"N

47°32'30"N

47°32'30"N

47°30'0"N

47°30'0"N

122°0'0"W

122°0'0"W

122°2'30"W 122°5'0"W

122°5'0"W

47°35'0"N

47°35'0"N

47°32'30"N

47°32'30"N

47°30'0"N

47°30'0"N

Qvr4

Tpt

Tpt

Tb

Tpr

Qal

Qvr4

Qvt

Tb

Qvt

Tpt

Tpr

Qvt

m

Qvr3

m

Qal

Qvt

Qf

Qvt

Qvr2

Qal

Qvt

Qvt

Tb

Qvr2

Qvt

Qva

Qoal

Qvi1

Qvr1

Qvr3

Qva

Qvi1

Qf

Ti

Qp

Qvt

Qvi2

Qvr2

Qvt

Qvt

Qvi2

Qf

Qvr5

Qvt

Qvt

Qpf

Qvr3

Qpf

Qvi2

Qvt

m

Qvr3

Qw

Qpo

Qmw

Qvi1

Qvt

Tb

Tb

Tpt

Tsc

m

Qvi1

Qw

Qf

m

Qva

Qvr3

Qvt

Qvr1

Qvt

Qvr1

Qw

Qva

Qvt

Qf

Qf

Tsc

Qw

Qvi1

Qpf

m

Qw

Qvr3

Qvt

Qvt

Qvt

Qvt

Qpf

Qva

Qvt

Qf

Qpff

Qf

m

Qvi2

Qvt

af

Qvi2

Qvi1

Qw

Qvt

Qpf

Qvr2

Qvi2

Qvr1

Qvr3

Qw

Tpr

Qvr3

Qvr2

Qvr3

Qvt

Qf

Qmw

Qvi2

Qvr3

Qw

Qpf

Qvr2

Qvt

Qw

Qf

Qw

Qvi2

Qw

Qw

Qvr2

Qva

Qpf

Qf

Qvi1

Qw

Tv

Qvr3

Qvi1

Qvt

Qvr3

Tb

Qf

Qvt

Qva

Qvt

Qf

Qvt

Qw

Qf

Qvt

Qpf

Tsc

Qmw

Qvr3

Qvt

Qvi1

Qvt

Qw

Tpt

Qw

Qvt

Qvr3

Qw

Qw

Qw

Tv

Qvt

Qvt

Qal

Qvr2

Qva

Qvr3

Qw

Qvr3

Qpf

Qva

m

Qal

Qva

Qva

 Qpog

Qvt

Qva

Qal

Qal

Qpf

Qw

Qal

Qvt

Tsc

Qvt

Qpog

Qpogt

Tpr

Qvt

Qal

Qmw

Qw

Tpr

Qpf

Qal

Qvi1

Qvi2

Qw

Qpff

Qvi2

Qpff

Qw

Tpt

Qva

Qw

Qf

Tpt

Qw

Qw

Qal

Qvt

Qvr3

Qpff

Qva

Tb

Qvr5

Qpogt

Qva

Qva

Qvr3 Qva

Tb

Qw

Qw

Tsc

Qvr3

Qvt

Qvr3

Qvt

Qvr3

Tpr

Qvt

Qob

Qw

Qw

Qf

Qvt

Tb

Qvt

Qvr3

Qvr1

Tb

Tb

Qva

Qvr3

Qal

Qal

Qw

Qpff

Qmw

Qva

Qmw

Qw

Qw

Tpt

Qvt

Qw

Qf

Qoal

Qw

Qw

Qva

Tpt

Qvt

Qpf

Qvt

Qva

Qva

Qva

Qvt

Qvr3

Qpff

Qva

Qvr1

Qvi1

Tsc

Qf

Qvt

Frontal

Qva

Tpt

Fault of Seattle Fault Zone

Qvt

85

30

18

40

30

45

30

30

85

30

20

35

25

30

40 40

35

45

35

30

20

45

35

40

40

35

40

12

12

50

50

55

45

55 50

40

50 40

40

45

40

35

40

85

74

34

25

28

44

44

30

Beta169462

etc.

Beta153518

& 153517

CAMS-23160 etc.

4

>

>

>

>

>

>

>

>

> >

>

>

>

>

>

>

>

> > >

>

>

>

>

>

>

>

>

>

> > >

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

>

> >

>

>

> > >

>

>

>

>

>

>

>

>

>

> >

>

>

>

>

> >

>

>

>

47o

 37' 00"

5' 

5263

5264

5267

5269

5270

(RENTON)

(MAPLE VALLEY) (HOBART) (FALL CITY)

(CARNATION)

(REDMOND)

(KIRKLAND)

T 24 N

T 23 N

32' 30"

35' 

5268

5271

5272

5273

5274

47o

 30'

122o

 00' 

122o

 00' 573 5 571 5 69 68 122o

 07' 30"

47o

 37' 30"

(MERCER ISLAND)

5266

47o

 30' 

122o

 07' 30" 573 572 2' 30" 570 571 567 574000m E

5262000m N

5' 

T 25 N

T 24 N

567

R 5 E R 6 E

5262000m N

T 24 N

T 23 N

5263

5264

32' 30"

5266

5267

5268

5269

5270

35' 

5271

5272

5273

5274

R 5 E R 6 E

A

T 25 N

T 24 N

Newcastle Hi l ls Antic l ine

Newcastle Hi l ls

0'

500'

Brunhes chron**

Matuyama chron

774 ka

18 ka

70 ka*

TERTIARY

Holocene Pleistocene

QUATERNARY

Qvt

Qva

Qpog

Fraser glaciation

Vashon stade

Qpff

Qob

Qpogt

Tv

Tpt Ti

Tpr

Tb

Tsc

Qvr5

Qvr1

Qvr2

Qvr3

Qvr4

Qvi1

Qvi2

Qpo

Qpf

m Qmw Qls Qw Qp Qf Qal Qoal af

Unconformity

BEDROCK

NONGLACIAL DEPOSITS

OLDER GLACIAL AND NONGLACIAL DEPOSITS

CORRELATION OF MAP UNITS

YOUNGER GLACIAL DEPOSITS

** Age of boundary from Sarna-Wojcicki and others (2000)

* Dates correspond to boundaries of the Olympia nonglacial interval (Booth and others, 2004)

Table 1. 14C ages from the map area

Sample

No. Site name Sampletype

Dated

unit Collected by

VP043 Vasa Park

E.trench2 charcoal 420±40 post Vashon

soil

B. Sherrod

(USGS)

VP033 B. Sherrod

VP014

VP009

VP035

VP001

S-25

S-1

_ Issaquah

 gravel

pit

charcoal

charcoal

charcoal

charcoal

charcoal

charcoal

charcoal

detrital

wood

Lab No.

Beta-183244

Beta-183243

Beta-183242

Beta-183241

Beta-171918

Beta-169462

Beta-153518

Beta-153517

CAMS-23160

(also 23170,

 71, 75, 76, 77)

10,530±50

9,830±50

11,670±50

10,350±40

11,550±40

4,610±40

34,870±50

14,450±90

B. Sherrod

B. Sherrod

B. Sherrod

B. Sherrod

K. Troost

(Univ. of WA)

K. Troost

Porter and

 Swanson

(1998)

Qmw

Qmw

Qmw

Qmw

Qmw

post Vashon

soil

Qob

Qva

Pretreatment

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

acid/alkali/acid

not specified

14C age, in

yr B.P.1

Vasa Park

W.trench3

Vasa Park

E.trench2

Vasa Park

E.trench2

Vasa Park

E.trench2

Vasa Park

E.trench2

Vasa Park

E.trench2

Vasa Park

W.trench3

1Present is considered to be 1950 A.D.

2Six reported 14C sites from same location at map scale. 3Two reported 14C sites from same location at map scale.

A’

Frontal fault of

Seattle Fault Zone

Qvt Qvt Qvr4

Qvt

A’

Qvt Qvt

Qvt

Qvi1

m

Lake Sammamish

1,000

2,000

FEET

Tsc

Qpf

A

Qal Qvi1

Qvt Qvi Qvr3 Qw 1 Qva

Qoal Qw

-1,000

-2,000

-3,000

-4,000

SEA LEVEL

Tpr Tpt Muldoon coal seam

Tpr

Tb

1,500

500

-500

-1,500

-2,500

-3,500

1,000

2,000

FEET

-1,000

-2,000

-3,000

-4,000

SEA LEVEL

1,500

500

-500

-1,500

-2,500

-3,500

Newcastle Hills Anticline 

Cougar Mountain 

1000 feet = 304.8 meters 

No Vertical Exaggeration 

bend in section

?

Tb

Tb

Qls Qls

DESCRIPTION OF MAP UNITS

NONGLACIAL DEPOSITS

Modified land (Holocene)—Fill or extensively graded natural deposits that 

obscure or substantially alter original deposit. Includes areas along 

Interstate Highway 90, office parks northwest of the City of Issaquah, 

gravel mines northeast of the city, rock quarries along Tibbetts Creek, 

coal mine spoils southwest of Issaquah, and areas of Lake Sammamish 

lakeshore development. Locally divided into artificial fill:

Artificial fill—Gravel, sand, and silt, intermixed with concrete and other 

materials placed as a direct result of human activity. Shown where 

borehole data provide sufficient information to delineate extent and 

where greater than about 3 m (10 ft) thick over at least tens of meters in 

lateral extent. Thin deposits of fill are present elsewhere throughout map 

area but are not mapped due to lack of information

Mass-wastage deposits (Holocene)—Colluvium, soil, and landslide debris 

having indistinct morphology. Mapped where underlying deposits and 

topography obscured. Numerous unmapped areas of mass-wastage 

deposits occur elsewhere in quadrangle along ravines and sidewalls of 

Lake Sammamish trough. Thicknesses typically about 3 m (10 ft) but 

locally may exceed 10 m (30 ft)

Landslide deposits (Holocene)—Diamictons composed of broken to 

internally coherent surficial deposits that have been transported 

downslope en masse by gravity. Discriminated from other mass-wastage 

deposits by thickness of identifiable slide deposits, by lateral continuity, 

and by presence of coherent blocks of geologic materials. On map, 

deposits are shown by dot pattern over inferred underlying unit(s). 

Landslides shown on the map beneath the surface of Lake Sammamish 

are taken from side-scan sonar profiling

Wetland deposits (Holocene)—Peat and alluvium; poorly drained and 

intermittently wet annually. Gradational with units Qal and Qp. Localities are compiled from King County (1983) 

Peat deposits (Holocene)—Peat accumulations greater than about 1 m thick 

and of mappable extent. Mostly in the valley of Issaquah Creek. Gradational with units Qw and Qal 

Fan deposits (Holocene)—Boulders, cobbles, sand, and diamict; deposited in 

lobate form where streams emerge from confining valleys onto areas of 

reduced gradients. Located along the shores of Lake Sammamish and at 

the edge of the Issaquah Creek valley. Gradational contact with unit Qal 

Alluvium (Holocene)—Cobble gravel, pebbly sand, and sandy silt, moderately sorted; deposited along major stream channels. Locally includes 

sediments of similar texture and age found in low-lying areas adjacent to 

Lake Sammamish, particularly beach and shallow lacustrine deposits that 

are not discriminated at map scale

Older alluvium (Holocene and Pleistocene)—Texturally equivalent to unit 

Qal but deposits lie at higher altitudes and typically have greater relief 

than the younger alluvium. May include deposits of late Fraser glaciation 

age that cannot be unequivocally assigned a pre-Holocene origin, 

particularly lake-bottom sediments associated with glacial Lake 

Sammamish that interfinger with flood-plain alluvium. Most extensive 

exposures are at Greenwood Point, southwest shore of Lake 

Sammamish, where the deposit forms a late Pleistocene or early Holocene fan of sediment that was shed off ice-contact deposits on the north 

flank of Cougar Mountain (peak 1459' in section 25, T. 24 N., R. 5 E.) 

YOUNGER GLACIAL DEPOSITS

Deposits of Vashon stade of the Fraser glaciation of Armstrong and 

others (1965) (Pleistocene) 

Recessional outwash deposits—Stratified sand and gravel, moderately to 

well sorted; less common silty sand and silt. Deposited along the four 

east-west-trending outwash channels that carried glacial meltwater 

westward into glacial Lake Sammamish from glacial Lake Snoqualmie 

during ice retreat. Very large foreset bedding is exposed in several of 

these deposits, reflecting delta growth into the glacial-age lake. The 

youngest recessional outwash, deposited during the lowest stand of 

glacial Lake Sammamish immediately prior to full ice retreat from the 

lowland (Thorson, 1980; Booth, 1990) is located just south of the town 

of Issaquah. In the eastern and west-central parts of the map area, 

recessional outwash deposits are subdivided into five deglacial stages on 

the basis of location and altitude. These deposits are indicated on the 

map by hyphenated subscripts, from youngest (Qvr5

) to oldest (Qvr1) 

stage units: 

Stage 5—Defined by a low delta just south of the Issaquah town center 

at altitudes between 30 and 45 m (100 and 150 ft). It probably reflects 

the last stage of the recessional lake history in the Puget Lowland 

(interval 14 of Booth, 1990). During this time, the entire set of interconnected Puget Lowland troughs (Lake Bretz of Waitt and Thorson, 1983) 

drained through a spillway at an altitude of about 60 m (200 ft) on the 

northeastern Olympic Peninsula, 50 km (30 mi) northwest of the map 

area. Isostatic rebound since deglaciation has elevated northern parts of 

the lowland more than southern parts because the Vashon-age ice sheet 

was thicker to the north. The relative uplift gradient is now observed to 

be 0.009 (about 1 m/km, or 5 ft/mi; Thorson, 1980; Booth, 1990). This 

gradient can be determined from the Stage-5 delta just south of the City 

of Issaquah, which lies about 30 km downgradient (approximately due 

south) from its controlling spillway and displays a modern altitude 

difference between the top of the delta (about equal to the lake elevation) 

and the lake spillway of 30 m (100 ft) 

Stage 4—Glacial Lake Snoqualmie drained via the Inglewood Channel 

near the north boundary of the map (Thorson, 1980; equivalent to 

interval 10–11 of Booth, 1990), which has a present-day spillway 

altitude of 110 m (360 ft). The level of glacial Lake Sammamish was 

unchanged from the end of Stage 3 during this time 

Stage 3—Deposition mainly consists of deposits from drainage of 

glacial Lake Snoqualmie through the valley of the North Fork Issaquah 

Creek (interval 8–9 of Booth, 1990). Drainage out of glacial Lake 

Sammamish at this time shifted successively northward through the 

Cedar Grove, Kennydale, and Eastgate channels, which have present-day 

spillway altitudes of 107 m (350 ft), 91 m (309 ft), and 98 m (323 ft), 

respectively (Thorson, 1980). The first two of these channels lie several 

kilometers south of the map; the third and last-occupied of these 

channels lies just west of the map boundary and is now the route of 

Interstate Highway 90 in that area. The quadrangle is inferred to have 

become ice-free by this time, and, therefore, high terraces near the north 

edge of the map are also assigned to this stage 

Stage 2—Encompasses drainage from glacial Lake Snoqualmie down 

the present East Fork Issaquah Creek valley in the eastern part of the 

map, where Interstate Highway 90 is now located (equivalent to interval 

5–6 of Booth, 1990). A large delta, built into glacial Lake Sammamish at 

altitudes about 120–150 m (400–500 ft) above modern sea level, forms 

the broad plateau underlying Tradition Lake along the east boundary of 

the map. The altitude of Lake Sammamish during this time was 

controlled by two spillways south of this delta: one was located along the 

Hobart Channel (present-day spillway altitude 150 m [490 ft]) at the 

head of the Issaquah Creek valley (Tabor and others, 2000) and the 

second one, carrying much less drainage and at a near-equivalent 

spillway altitude, was located at the upstream (southwest) divide of the 

Tibbetts Creek valley, about 3 km (2 mi) southwest of Issaquah. East of 

the town of Issaquah, these recessional, late-Vashon-age deposits mantle 

a proglacial delta of early Vashon age (Porter and Swanson, 1998) 

Stage 1—Consists of deposits prior to significant drainage into the 

Sammamish trough from the Snoqualmie valley. Near the south end of 

Lake Sammamish, extensive deposits of valley-wall outwash and 

ice-contact sediments (see unit Qvi) accumulated during this time. 

South-flowing meltwater drained up the present-day valleys of both 

Tibbetts Creek and Issaquah Creek, reflecting a reversal of drainage 

directions that occurred in these valleys between late-glacial and modern 

times 

Ice-contact deposits—Similar in texture to unit Qvr but contain a much 

higher percentage of silt intermixed with granular sediments that result in 

poorly sorted stratified sediment and local diamicts. Also mapped in 

areas that have collapse features, such as the closed depressions between 

Laughing Jacobs Lake and Beaver Lake, suggesting deposition against 

stagnant melting ice. These deposits are indicated on the map by 

subscripts, from youngest (unit Qvi2

) to oldest (unit Qvi1). They follow 

the same age convention described for unit Qvr and are based on the 

position(s) of the ice tongue in the Lake Sammamish valley necessary to 

divert water through each associated spillway (and its correspondingly 

numbered recessional deposit)

Stage 2—Consists of deposits along the southern meltwater channel 

through the Laughing Jacobs Lake area

Stage 1—Consists of deposits flanking both sides of the Lake 

Sammamish trough, in the vicinity of Monahan (east side) and above 

Greenwood Point (west side), and along the valleys of the Tibbetts Creek 

and lower Issaquah Creek 

Till—Compact diamict containing subrounded to well-rounded clasts, 

glacially transported and deposited. Generally forms an undulating 

surface a few meters to a few tens of meters thick. Also found more 

sporadically within areas of ice-contact deposits (unit Qvi)

Advance outwash deposits—Well-sorted sand and gravel; deposited by 

streams issuing from advancing ice sheet. Generally not oxidized; mostly 

devoid of silt or clay, except near the base of the unit. Well exposed 

along much of the Sammamish trough sidewall. High susceptibility to 

water erosion has resulted in large prehistoric ravines; runoff from 

recently urbanized areas has resulted in rapidly expanding new gullies 

OLDER GLACIAL AND NONGLACIAL DEPOSITS

Undifferentiated sedimentary deposits of pre-Fraser glaciation age 

(Pleistocene)—Comprises a variety of deposits that underlie Vashon-age 

deposits and that otherwise lack numeric age control. Includes unoxidized to slightly oxidized silt and clay that may locally include 

Olympia-age or early-Vashon-age lacustrine deposit and slightly to 

moderately oxidized sand and gravel previously mapped by Booth and 

Minard (1992) as unit Qob. Locally divided into fine-grained deposits:

Fine-grained deposits—Predominantly silt and clay

Olympia beds of Minard and Booth (1988) (Pleistocene)—Sand and 

gravel, slightly to moderately oxidized; deposited during nonglacial time 

in the Puget Lowland by rivers. Mapped only near the west map boundary; one radiocarbon sample provides numeric age control (24,870±50 yr 

B.P.)

Deposits of pre-Olympia age (Pleistocene)—Interbedded sand, gravel, silt, 

and diamicts of indeterminate age and origin. Very dense. Locally 

divided into glacial deposits:

Glacial deposits—Weakly to strongly oxidized silt, sand, gravel, and rare 

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

be of pre-Olympia age. Sediment is of inferred glacial (northern) origin, 

based on presence of till and clasts or mineral grains requiring southward 

ice-sheet transport. Locally divided into glacial till:

Glacial till—Predominantly till or other diamict where thick enough to 

show at map scale

BEDROCK

Sandstone and conglomerate (Tertiary)—Sandstone, conglomerate, tuff, 

and volcaniclastic sandstone, exposed above the southwest and southeast 

shores of Sammamish Lake. Contains interbeds of lignite, including 

nearly coherent logs. Bedding is concordant with underlying Blakeley 

Formation, but stratigraphic position and low degree of lithification had 

led some previous workers to assign a Quaternary age to this deposit (for 

example, Liesch and others, 1963). However, available K-Ar ages from 

one locality range from 9.3 to 14.7 Ma (Yount and Gower, 1991); Ar/Ar 

laser fusion dating from this unit yields an age of 11.40±0.61 Ma 

Blakeley Formation of Weaver (1912) (Tertiary)—Medium-grained 

sandstone, coarse-grained sandstone, conglomerate, airfall tuff, 

tuffaceous sandstone, and minor siltstone, fresh to highly weathered. 

Massive to well bedded. Quartz, feldspar, and lithic volcanic grains 

present in varying amounts. Deposited in a shallow marine to coastal 

environment; foraminifera collected near the top of this unit yielded a 

Zemorrian (middle to late Oligocene) age (Walsh, 1984). Distinguished 

from rocks of underlying Puget Group by presence of marine fossils and 

by the absence of mica in sandstone facies relative to those of the Renton 

Formation. Mapped contacts with underlying Puget Group largely 

adopted from Walsh (1984) 

Volcanic rocks (Tertiary)—Slightly porphyritic andesite that forms a 

topographic knob along the North Fork Issaquah Creek valley. Occupies 

the same stratigraphic relation to the underlying Renton Formation as 

does the Blakeley Formation of Weaver (1912); probably interbedded 

with Renton Formation (Tpr) 

Intrusive rocks (Tertiary)—Porphyritic andesitic to dacitic stock in 

southeast corner of map area; forms the west slopes of Tiger Mountain 

and east slope of Squak Mountain just south of the map area. Speculated 

by Vine (1962) to be subvolcanic intrusion corresponding to the 

extrusive Tukwila Formation. Contact relations with adjacent unit Tpt

not exposed 

Puget Group (Tertiary) 

Renton Formation—Nonmarine fine- to medium-grained arkosic 

sandstone and siltstone containing abundant subbituminous coal beds 

and carbonaceous shale

Tukwila Formation—Andesitic to dacitic volcanic sandstone, siltstone, 

shale, tuff-breccia, tuff, volcanic mudflow (lahar), carbonaceous shales, 

and minor lava flows or sills. Typically massive; only local sedimentary 

interbeds indicate structure. K-Ar age on plagioclase from tuff-breccia at 

top of unit, about 3 km west of quadrangle, yielded an age of 42.0±2.4 

Ma (Turner and others, 1983)

EXPLANATION OF MAP SYMBOLS

Drowned trees

Contact

Fault—Dashed where approximate; dotted where concealed

Anticline—Dashed where approximate; dotted where concealed

Syncline—Dashed where approximate; dotted where concealed

Structural contour—0' and 500' structure contours drawn on the Muldoon 

coal seam (Renton Formation). Dashed where approximate

Strike and dip of beds

Inclined

Bedding tops recognized

Overturned bed

Forset beds in fluvial deposits

14C age locality—See table 1 for ages

Exploration Sites

Field exposure with station number

Geotechnical boring

Geotechnical test pit

Cone penetometer test (CPT)

Monitoring or water well

Density probe

GEOLOGIC SUMMARY

INTRODUCTION

The Issaquah area includes several of the most outstanding geologic features of the 

eastern Puget Lowland region. Folds have warped thousands of meters of Tertiary 

sedimentary and volcanic rocks. Several hundred meters of both glacial and postglacial 

sediment have accumulated in a deep glacial trough, which is now partly occupied by 

Lake Sammamish but which was previously the conduit for massive volumes of meltwater during ice-sheet occupation and retreat. The eastern projection of an east-westoriented crustal structure, which reflects Tertiary through Holocene fault displacement, 

extends across the eastern part of the map area (Gower and others, 1985; Yount and 

others, 1985). 

In addition to these geologic features, some of the most rapid human alteration of 

the landscape in the entire Puget Lowland has occurred here. Since the 19th century, coal 

was extensively mined and, since the early 1980s, the region has been overtaken by 

urbanization. In places, this alteration has dramatically accelerated the rate of geomorphic 

processes. For example, the hillsides have been regraded as a result of mining and 

quarries throughout the southern one-third of the quadrangle; stream channels have 

recently incised above the eastern shores of Lake Sammamish; and sediments have 

deposited on the lakeshore and into the lake itself. 

PREVIOUS MAPPING

This map follows prior mapping by Booth and Minard (1992), who mapped the 

geology of the Issaquah 7.5′ quadrangle. They mapped outcrops exposed in road cuts, 

stream banks, construction excavation sites, and a few selected well logs. Previous work, 

particularly Liesch and others (1963) and Curran (1965), also provided a useful introduction to the area; many of the bedrock contacts are compiled from Walsh (1984). More 

recently, the digital compilation of geotechnical explorations and water-well logs and 

LIDAR (LIght Distance And Ranging) topography from airborne laser rangefinding 

(Haugerud and others, 2003) provide a wealth of new geologic data. Additional fieldwork 

in 2002 and 2003 emphasized both reinterpretation of the stratigraphy along the 

nearshore areas of Lake Sammamish and investigations of the fault just west of Lake 

Sammamish near Interstate 90. This map thus reflects the current status of geologic 

information and understanding in this region of the Puget Lowland.

ACKNOWLEDGMENTS

Particular acknowledgments are due our colleagues who have shared geologic data, 

insights, and interpretations throughout the current period of additional mapping: Brian 

Sherrod, Ralph Haugerud, and Ray Wells (USGS); Patrick Pringle (Washington State 

Department of Natural Resources); John Bethel (King County Water and Land Resources 

Division); and Curtis Koger and Jennifer Hilden Saltonstall (Associated Earth Sciences, 

Inc.). Technical reviews were provided by Brian Sherrod (USGS) and Joe Dragovich 

(Washington State Department of Natural Resources). Special thanks are due Jim Minard 

(USGS), whose preliminary work in the map area and general enthusiasm for unraveling 

the distribution and history of geologic deposits across the region have provided lasting 

guidance for those who have followed in his footsteps.

REGIONAL HISTORY AND STRATIGRAPHY

BEDROCK

The east-central Puget Lowland is underlain by Eocene to Miocene volcanic and 

sedimentary rocks (Yount and Gower, 1991; Tabor and others, 2000), warped into a series 

of northwest-trending folds. In the Issaquah area, these Tertiary rocks are exposed only in 

the southern half of the map area. Younger glacial deposits have lapped onto both limbs 

of the largest of these folds, the Newcastle Hills anticline of Weaver (1916), a bedrock 

high that extends 50 km to the northwest from the front of the Cascade Range 

(Mullineaux, 1970) towards the center of the Puget Lowland. 

In the map area, the rocks exposed in the core of the Newcastle anticline are 

assigned to the Puget Group, first named by White (1888). The Puget Group was later 

revised to include a lower assemblage of volcanic sedimentary rocks, the Tukwila 

Formation, and an upper unit of arkosic sedimentary rocks and coal, the Renton Formation (Vine, 1962, 1969). The Tukwila Formation is named for the city of Tukwila, about 8 

km west-southwest of the map area, where the formation primarily consists of volcanic 

sandstone, siltstone, and shale along with some volcanic conglomerate, tuff, and a few 

carbonaceous shales. Fragments of wood and other plant remains are common throughout 

the Tukwila Formation. Volcanic rocks, particularly welded tuffs, are more abundant in 

this map area than farther west. 

The Renton Formation is named for exposures in and around the city of Renton, 

located about 5 km west of the map area. The formation conformably overlies the 

Tukwila Formation and includes the Renton coal measures, which were extensively 

mined throughout much of the Newcastle Hills in Renton and Issaquah during the late 

19th and early 20th centuries. The formation consists mostly of fine- to medium-grained 

arkosic sandstone and lesser amounts of siltstone, sandy shale, coal, and carbonaceous 

shale. 

The clastic, fluvial rocks of the Puget Group were derived chiefly from a distant 

eastern source of granites or gneisses (Weaver, 1937). Intermittently, volcanic debris, 

probably ejected from nearby vents, clogged the sluggish streams and locally dominated 

sedimentation. Sediments of the group probably were deposited on a low-lying coastal 

plain just east of a slowly subsiding basin (Buckovic, 1979). Ages from the Puget Group 

range from middle to late Eocene, although none of the ages are derived from rocks 

exposed in the map area (Waldron, 1962; Turner and others, 1983; Yount and Gower, 

1991). Immediately east of the map area, Vine (1969) estimated a minimum thickness for 

the Puget Group of 3,400 m (11,200 ft), a thickness that is nearly equaled by the subsurface projection of exposures in the map area (see cross section). 

Overlying the Puget Group, exposures of the Blakeley Formation of Weaver (1912) 

overlook the south end of Lake Sammamish. The Blakeley Formation consists primarily 

of medium-grained sandstone that contains local marine fossils that yield a Zemorrian 

(middle to late Oligocene) age (Walsh, 1984). Bedding is roughly conformable with the 

underlying Puget Group. In the map area, the exposed thickness of the unit is about 3,400 

m (11,000 ft).

The youngest Tertiary bedrock (Tsc) exposed in the quadrangle is not formally 

named. It conformably overlies the Blakeley Formation and is readily distinguished from 

the Blakeley by overall coarser sediment size, terrestrial plant fossils, and low degree of 

lithification. These rocks were once assigned a Quaternary age (Liesch and others, 1963). 

However, Yount and Gower (1991) report K-Ar ages of 14.7 and 9.3 Ma from an air-fall 

tuff in this unit on the west side of Sammamish Lake; T.J. Walsh and P.T. Pringle 

(Washington Division of Geology and Earth Resources) collected pumice overlying a 

9-m-thick vitric tuff from this same area and obtained Ar/Ar laser fusion ages of 11.12 

Ma on plagioclase and 12.35, 11.12, and 11.14 Ma, averaging 11.40+0.61 Ma (dating by 

Berkeley Geochronology Center, Berkeley, Calif.). Bedding is concordant with underlying Blakeley Formation; bedding dips mainly to the north. Although only a few hundred 

meters are now exposed, the uppermost strata almost certainly have been downdropped 

by the Seattle Fault and subsequently covered by Quaternary deposits. 

Although we do not formally correlate this unit (Tsc) with other named deposits of 

the Puget Lowland, it was likely deposited near-contemporaneously with the Blakely 

Harbor Formation (Fulmer, 1975), whose type section is about 30 km west of the 

quadrangle and consists of dated Miocene-age terrestrial sediments. On the regional 

aeromagnetic survey map of the Puget Lowland (Blakely and others, 2002), the rocks 

exposed at both the Blakely Harbor Formation type locality and in the map area display a 

distinctive high-susceptibility signature that can be traced continuously between the two 

areas, which suggests both a lateral continuity and a similar lithology.

QUATERNARY DEPOSITS

Deposits that form a discontinuous record of glacial and interglacial deposition 

throughout much of the Quaternary period overlie the Tertiary rocks. Originating in the 

mountains of British Columbia, multiple invasions of glacial ice into the Puget Lowland 

defined the southernmost extent of the Cordilleran ice sheet of northwestern North 

America. During each successive glaciation, ice advanced into the lowland as a broad 

tongue called the Puget lobe (Bretz, 1913). 

In the map area, glacial deposits are unequivocally assigned only to the most recent 

of these glacial advances, the Vashon stade of the Fraser glaciation of Armstrong and 

others (1965). Climaxing about 17,000 years ago, ice occupation of the Puget Lowland 

during the Vashon stade probably spanned less than 2,000 years in total (Porter and 

Swanson, 1998). Scattered deposits (unit Qpf) in the southern part of the map area 

suggest an earlier glacial advance, although no assignment or regional correlation can be 

made because of poor exposure and poor age constraint. 

Before the Vashon stade, nonglacial conditions prevailed in the map area for at least 

several tens of thousands of years. This nonglacial interval, named the Olympia interglaciation by Armstrong and others (1965), is associated with a wide variety of nonglacial 

deposits across much of the Puget Lowland (Troost, 1999). Booth and Minard (1992) 

assigned lightly to moderately oxidized fluvial sand and gravel in the northern part of the 

Issaquah quadrangle to this nonglacial interval (see also Minard and Booth, 1988) on the 

basis of stratigraphic, textural, and weathering characteristics. The absence of confirming 

radiocarbon dates, however, coupled with reported Olympia-age deposits over 100 m 

higher just a few kilometers north of the map area (Saltonstall and others, 2003), suggest 

that only the more general pre-Fraser age assignment (unit Qpf) is warranted. Similarly, 

overlying silt and clay that were previously mapped (Booth and Minard, 1992) as 

post-Olympia-age deposits are also now assigned the more general (but probably more 

correct) “pre-Fraser age” unit name, discriminated where possible from the underlying 

deposits only by texture. The unequivocal start of the Vashon stade of the Fraser glaciation of Armstrong and others (1965) is marked by the thick deposits of outwash (Qva) 

followed by till (Qvt) derived from the advancing ice sheet. 

A variety of glacial and postglacial geologic processes have created and modified 

the Lake Sammamish trough. The trough is weakly reflected in the folded structures of 

the underlying bedrock, but the modern surface expression of the trough is more 

pronounced than the underlying warping. That surface expression must largely predate 

the ice retreat, because lodgment till of Vashon age (Qvt) mantles some of the sidewalls 

and approaches present-day water level in the northern part of the trough. Slightly 

younger ice-contact sediments are plastered against the eastern wall at Monohan (Qvi1

). 

Finally, deposits of the Inglewood delta, a late-glacial recessional feature at the north 

edge of the map (included in unit Qvr4), approach and may extend below present-day 

lake level, well within the confines of the trough itself. Thus, the trough existed prior to 

final retreat of the ice sheet because these Vashon-age deposits mantle or fill the Lake 

Sammamish trough.

Geologic activity since glaciation is most pronounced along the walls of the 

Sammamish trough, where deposits of the ice occupation and retreat have been stripped 

away by mass movement to reveal the crudely horizontal layering of the underlying early 

glacial and preglacial material. The sequence of these older deposits, primarily outwash 

sand and gravel deposits derived from the advancing ice sheet (Qva) that overlie older 

silt and clay deposits (Qpf), results in a particularly active Holocene environment. Due to 

the underlying silt and clay deposits that perch groundwater, landslides commonly occur 

at the contact between unit Qva and unit Qpf. These stratigraphic conditions are common 

along much of the west wall of the trough and the eastern wall above Jensens Cove, 

although the resulting landslides are mainly too small or are obscured by trees and human 

development to show at map scale. The noncohesiveness of the overlying outwash 

deposits, in addition, has favored rapid and severe erosion by surface water throughout 

areas underlain by unit Qva.

In the map area, landslides occur in several other geologic settings at many scales, 

from large mappable slides involving bedrock to small and vegetation-obscured mass 

movement of glacial sediments too small or indistinct to show at map scale. Landslides 

shown on the map beneath the surface of Lake Sammamish are mapped from side-scan 

sonar profiling by Mark L. Holmes and Robert E. Karlin as depicted in Gonzalez (2003). 

The now-drowned landslide off Greenwood Point at the south end of Lake Sammamish 

has a rooted old-growth forest; the tree tops are exposed a few feet above the lake level 

(Logan and Walsh, 1995). The landslide has been attributed to an earthquake on the 

Seattle Fault about 1,000 years ago (Bucknam and others, 1992), based on the age of one 

such rooted tree with bark. The age of the outermost rings of the tree, 1,050±60 14C yr 

B.P. (Logan and others, 1998), is indistinguishable from the age of trees rooted in a 

landslide in Lake Washington and the age of organic material in a tsunami deposit at 

West Point on the west side of Seattle (Atwater and Moore, 1992). 

STRUCTURE

The map area contains the northernmost exposures of Tertiary bedrock (units Tb and 

Tsc) in the east-central Puget Lowland, exposed at the north edge of the Seattle uplift 

(Blakely and others, 2002). In the southern part of the map area, older bedrock (units Tpt

and Tpr) lies at or near the surface; but to the north, the bedrock surface descends steeply 

(Jones, 1996) and is covered by many hundreds of meters of Quaternary deposits. 

This observed pattern in the Tertiary bedrock, namely exposure to the south and 

deep burial to the north, continues along a west-trending lineament between Lake 

Sammamish and Restoration Point on Bainbridge Island, 30 km west of the map area. 

Danes and others (1965) first identified and mapped the lineament as a Quaternary fault 

zone, and it was shown as such on the 1992 edition of this geologic map (Booth and 

Minard, 1992). The lineament is now widely recognized and is named the Seattle Fault, 

although detailed structure of the fault is still subject to significant uncertainty (compare, 

for example, Pratt and others, 1997; Johnson and others, 1999; ten Brink and others, 

2002; Brocher and others, 2004). Therefore, the subsurface representation of the fault 

zone in cross section is speculative, but we attempt to remain consistent with (1) the 

pattern of surface exposures, (2) the suggestion of blind splays off the main fault 

suggested by seismic profiling (Liberty, 2003; Liberty and Pratt, 2008), and the depth-tobedrock data compiled by Jones (1996) but which is admittedly sparse in this part of the 

Puget Lowland. The mapped fault trace displayed here, namely the surface projection of 

the frontal fault of the Seattle Fault Zone, follows the high-amplitude geophysical 

anomaly associated elsewhere with Miocene bedrock (Blakely and others, 2002, their 

fig. 4) and, in the map area, with faults observed in trenches at Vasa Park (west edge of 

map) and faults in a seismic-reflection profile east of Pine Lake (east edge of map) 

(Liberty, 2003, his profile SM1)

Folded bedrock is associated with the frontal fault of the Seattle Fault Zone. East of 

Lake Sammamish and about 1 km south of the fault trace, locally very steep and 

overturned dips involve (and must postdate deposition of) unit Tsc. A small anticline 

southwest of Greenwood Point, also about 1 km south of the projected fault trace, is 

expressed by opposing dips in unit Tb. The rocks of unit Tsc are apparently coaxially 

folded with the Newcastle Hills anticline about 6 km to the south, which shows about 10 

km of structural relief (Vine, 1962; Walsh, 1984). The structural relief indicates a rate of 

about 1 mm/yr of north-south shortening since about 10 Ma, a value that lies in the range 

of crustal strain rates that Booth and others (2004) inferred from deformed Quaternary 

strata farther west along the axis of the Puget Lowland. Also, fault studies near Vasa Park 

indicate at least one Holocene event has produced surface ground rupture (Sherrod, 

2002).

The only other fault shown on the map appears in the southwest corner; it is exposed 

a short distance west of the map boundary. The fault was encountered in a mine at 

Coalfield at a depth of about 60 m (200 ft), where the coal that dips steeply to the south at 

its outcrop is faulted and becomes overturned (Warren and others, 1945; see Schasse and 

others (1994) for coal mine map information). The dip of the fault is not constrained, but 

the sense of drag suggests that it is down-to-the-south. This fault forms the southern 

boundary of the Seattle Fault Zone; it is coincident with the Orchard Point Fault of 

Blakely and others (2002) and correlates with the Lowman Beach fault strand of Troost 

and others (2005).

The structure contours, across the southern part of the map, trace the nearly continuous Muldoon coal seam, a heavily mined seam in the middle of an area of abundant coal 

strata; data are taken from original mine maps compiled by Walsh (1983). The offset in 

this bed, shown 3 km south of Lake Sammamish, is the only fault known to cut the coal 

measures for a distance of about 16 km along strike (Walsh and Lingley, 1991), although 

the dashed part of the structure contour can only be inferred because the coal has been 

eroded by glacial activity. The absence of significant offsets in this well-constrained coal 

layer suggests that, in the eastern part of the Seattle Fault Zone, significant deformation 

between individual fault strands is not as widespread as farther west (Nelson and others, 

2003; Troost and others, 2005).

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. 

Atwater, B.F., and Moore, A.L., 1992, A tsunami about 1,000 years ago in Puget Sound, 

Washington: Science, v. 258, no. 5,088, p. 1,614–1,617.

Blakely, R.J., Wells, R.E., Weaver, C.S., and Johnson, S.Y., 2002, Location, structure, and 

seismicity of the Seattle fault zone, Washington—Evidence from aeromagnetic 

anomalies, geologic mapping, and seismic-reflection data: Geological Society of 

America Bulletin, v. 114, no. 2, p. 169–177.

Booth, D.B., 1987, Timing and processes of deglaciation along the southern margin of the 

Cordilleran ice sheet, in Ruddiman, W.F., and Wright, H.E., Jr., eds., North America 

and adjacent oceans during the last deglaciation: Boulder, Colorado, Geological 

Society of America, The Geology of North America, v. K-3, p. 71–90. 

Booth, D.B., 1990, Surficial geology of the Skykomish and Snoqualmie Rivers area, 

Snohomish and King Counties, Washington: U.S. Geological Survey Miscellaneous 

Investigations Series Map I–1745, scale 1:50,000. 

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 Minard, J.P., 1992, Geologic map of the Issaquah quadrangle, King 

County, Washington: U.S. Geological Survey Miscellaneous Field Studies Map 

MF–2206, scale 1:24,000.

Booth, D.B., Troost, K.G., Clague, J.J., and Waitt, R.B., 2004, 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.

Bretz, J H., 1913, Glaciation of the Puget Sound region: Washington Geological Survey 

Bulletin 8, 244 p. 

Brocher, T.M., Blakely, R.J., and Wells, R.E., 2004, Interpretation of Seattle uplift, 

Washington, as a passive roof duplex: Bulletin of the Seismological Society of 

America, v. 94, no. 4, p. 1,379–1,401. 

Bucknam, R.C., Hemphill-Haley, E., and Leopold, E.B., 1992, Abrupt uplift within the 

past 1,700 years at southern Puget Sound, Washington: Science, v. 258, no. 5,088, p. 

1,611–1,614.

Buckovic, W.A., 1979, The Eocene deltaic system of west-central Washington, in 

Armentrout, J.M., Cole, M.R., and TerBest, Harry, Jr., eds., Cenozoic paleography of 

the western United States: Society of Economic Paleontologists and Mineralogists, 

Pacific Section, Pacific Coast Paleogeography Symposium 3, p. 147–164.

Crandell, D.R., 1963, Surficial geology and geomorphology of the Lake Tapps quadrangle, Washington: U.S. Geological Survey Professional Paper 388–A, 84 p. 

Curran, T.A., 1965, Surficial geology of the Issaquah area, Washington: Seattle, Wash., 

University of Washington, Department of Geological Sciences, M.S. thesis, 57 p. 

Danes, Z.F., Bonno, M., Brau, J.E., Gilham, W.D., Hoffman, T.F., Johansen, D., Jones, 

M.H., Malfait, Bruce, Masten, J., and Teague, G.O., 1965, Geophysical investigation 

of the southern Puget Sound area, Washington: Journal of Geophysical Research, v. 

70, no. 22, p. 5,573–5,580.

Fulmer, C.V., 1975, Stratigraphy and paleontology of the type Blakeley and Blakely 

Harbor Formations, in Weaver, D.W., Hornaday, G.R., and Tipton, Ann, eds., 

Paleogene symposium and selected technical papers [proceedings]; conference on 

future energy horizons of the Pacific Coast: American Association of Petroleum 

Geologists, Pacific Section, v. 50, 50th joint annual meeting of Pacific Sections of 

American Association of Petroleum Geologists, Society of Economic Paleontologists and Mineralogists, and Society of Exploration Geophysicists, Long Beach, 

Calif., April 23–26, 1975, p. 210–271.

Gonzalez, F.I., comp., 2003, Puget Sound tsunami sources—2002 workshop report: 

NOAA/Pacific Marine Environmental Laboratory Contribution No. 2526, 36 p.

Gower, H.D., Yount, J.C., and Crosson, R.S., 1985, Seismotectonic map of the Puget 

Sound region, Washington: U.S. Geological Survey Miscellaneous Investigations 

Series Map I–1613, scale 1:250,000. 

Haugerud, R.A., Harding, D.J., Johnson, S.Y., Harless, J.L., Weaver, C.S., and Sherrod, 

B.S., 2003, High-resolution Lidar topography of the Puget Lowland, 

Washington—A bonanza for earth science: GSA Today, v. 13, no. 6, p. 4–10, doi: 

10.1130/1052-5173(2003)13<0004:HLTOTP>2.0.CO;2.

Johnson, S.Y., Dadisman, S.V., Childs, J.R., and Stanley, W.D., 1999, Active tectonics of 

the Seattle fault and central Puget Sound, Washington—Implications for earthquake 

hazards: Geological Society of America Bulletin, v. 111, no. 7, p. 1,042–1,053.

Jones, M.A., 1996, Thickness of unconsolidated deposits in the Puget Sound Lowland, 

Washington and British Columbia: U.S. Geological Survey Water-Resources 

Investigations Report 94–4133, scale 1:455,000.

King County, 1983, King County Wetlands: Seattle, Washington, King County Planning 

Division, 3 volumes. 

Liberty, L.M., 2003, Seismic profiling of the Seattle fault, Lake Sammamish region, 

Washington: U.S. Geologic Survey National Earthquake Hazard Reduction Program, 

Final Report, project 03HQGR0132, accessed 10 October 2005 at 

http://cgiss.boisestate.edu/EQH/Seattle/NEHRP_03HQGR0132_Liberty.pdf

Liberty, L.M., and Pratt, T.L., 2008, Structure of the Eastern Seattle Fault Zone, Washington State—New insights from seismic reflection data: Bulletin of the Seismological 

Society of America, v. 84, no. 4, p. 1,681–1,695.

Liesch, B.A., Price, C.E., and Walters, K.L, 1963, Geology and ground water resources of 

northwestern King County, Washington: Washington State Water Supply Bulletin 

No. 20, 241 p., scale 1:48,000. 

Logan, R.L., Schuster, R.L., Pringle, P.T., Walsh, T.J., and Palmer, S.P., 1998, Radiocarbon ages of probable coseismic features from the Olympic Peninsula and Lake 

Sammamish, Washington: Washington Geology, v. 26, no. 2/3, p. 59–67.

Logan, R.L., and Walsh, T.J., 1995, Evidence for a large prehistoric seismically induced 

landslide into Lake Sammamish: Washington Geology, v. 23, no. 4, p. 3–5.

Minard, J.P., 1983, Geologic map of the Edmonds East and part of the Edmonds West 

quadrangles, Washington: U.S. Geological Survey Miscellaneous Field Studies Map 

MF–1541, scale 1:24,000. 

Minard, J.P., 1985, Geologic map of the Maltby quadrangle, Snohomish and King 

Counties, Washington: U.S. Geological Survey Miscellaneous Field Studies Map 

MF–1746, scale 1:24,000. 

Minard, J.M., and Booth, D.B., 1988, Geologic map of the Redmond 7.5' quadrangle, 

King and Snohomish Counties, Washington: U.S. Geological Survey Miscellaneous 

Field Studies Map MF–2016, scale 1:24,000. 

Mullineaux, D.R., 1970, Geology of the Auburn, Renton, and Black Diamond quadrangles, King County, Washington: U.S. Geological Survey Professional Paper 672, 

92 p. 

Nelson, A.R., Johnson, S.Y., Kelsey, H.M., Wells, R.E., Sherrod, B.L., Pezzopane, S.K., 

Bradley, Lee-Ann, Koehler, R.D., III, and Bucknam, R.C., 2003, Late Holocene 

earthquakes on the Toe Jam Hill fault, Seattle fault zone, Bainbridge Island, Washington: Geological Society of America Bulletin, v. 115, no. 11, p. 1,388–1,403. 

Porter, S.C., and Swanson, T.W., 1998, Radiocarbon age constraints on rates of advance 

and retreat of the Puget lobe of the Cordilleran ice sheet during the last glaciation: 

Quaternary Research, v. 50, p. 205–213.

Pratt, T.L., Johnson, S.Y., Potter, C.J., Stephenson, W.J., Finn, C.A., 1997, Seismic 

reflection images beneath Puget Sound, western Washington State; the Puget 

Lowland thrust sheet hypothesis: Journal of Geophysical Research, B, Solid Earth 

and Planets, v. 102, p. 27,469–27,489.

Saltonstall, J.H., Koger, C.J, Sweet, S., and Thompson, S.S., 2003, Olympia age paleotopographic influences on Vashon glaciofluvial sedimentation beneath eastern Bear 

Creek plateau, King County, Washington [abs.]: Geological Society of America 

Abstracts with Programs, v. 35, no. 6, p. 109.

Sarna-Wojcicki, A.M., Pringle, M.S., Jr., and Wijbrans, J., 2000, New 40Ar/39Ar age of the 

Bishop Tuff from multiple sites and sediment rate calibration for the MatuyamaBrunhes boundary: Journal of Geophysical Research, B, Solid Earth, v.105, no. B9, 

p. 21,431–21,443. 

Schasse, H.W., Koler, M.L., Eberle, N.A., and Christie, R.A., 1994, The Washington 

State coal mine map collection—A catalog, index, and user's guide: Washington 

Division of Geology and Earth Resources Open File Report 94-7, 109 p., accessed 

July 24, 2003, at http://www.dnr.wa.gov/geology/pdf/ofr94-7.pdf.

Sherrod, B.L., 2002, Late Quaternary surface rupture along the Seattle fault zone near 

Bellevue, Washington [abs.]: Eos, American Geophysical Union Transactions, v. 83, 

no. 47, Supplement, p. F1074–F1075.

Tabor, R.W., Frizzell, V.A., Jr., Booth, D.B., and Waitt, R.B., 2000, Geologic map of the 

Snoqualmie Pass 30- x 60-minute quadrangle, Washington: U.S. Geological Survey 

Geologic Investigations Series I–2538, scale 1:100,000 

[http://pubs.usgs.gov/imap/i2538].

ten Brink, U.S., Molzer, P.C., Fisher, M.A., Blakely, R.J., Bucknam, R.C., Parsons, T.E., 

Crosson, R.S., and Creager, K.C., 2002, Subsurface geometry and evolution of the 

Seattle fault zone and the Seattle basin, Washington: Seismological Society of 

America Bulletin, v. 92, no. 5, p. 1,737–1,753.

Thorson, R.M., 1980, Ice sheet glaciation of the Puget Lowland, Washington, during the 

Vashon stade: Quaternary Research, v. 13, p. 303–321. 

Troost, K.G., 1999, The Olympia nonglacial interval in the southcentral Puget Lowland, 

Washington: Seattle, University of Washington, M.S. thesis, 123 p.

Troost, K.G., Booth, D.B., Wisher, A.P., and Shimel, S.A., 2005, The geologic map of 

Seattle: U.S. Geological Survey Open-File Report 2005–1252, scale 1:24,000 

[http://pubs.usgs.gov/of/2005/1252].

Turner, D.L., Frizzell, V.A., Jr., Triplehorn, D.M., and Naeser, C.W., 1983, Radiometric 

dating of ash partings in coal of the Eocene Puget Group, Washington—Implications 

for paleobotanical stages: Geology, v. 11, no. 9, p. 527–531.

Vine, J.D., 1962, Stratigraphy of Eocene rocks in a part of King County, Washington: 

Washington Division of Mines and Geology Report of Investigations 21, 20 p. 

Vine, J.D., 1969, Geology and coal resources of the Cumberland, Hobart, and Maple 

Valley quadrangles, King County, Washington: U.S. Geological Survey Professional 

Paper 624, 67 p., 4 pls., scale 1:24,000.

Waitt, R.B., Jr., and Thorson, R.M., 1983, The Cordilleran ice sheet in Washington, 

Idaho, and Montana, in Porter, S.C., and Wright, H.E., Jr., eds., Late-Quaternary 

environments of the United States: Minneapolis, University of Minnesota Press, v. 1, 

p. 53–70.

Waldron, H.H., 1962, Geology of the Des Moines quadrangle, Washington: U.S. Geological Survey Geologic Quadrangle Map GQ–159, scale 1:24,000.

Walsh, T.J., 1983, Map of coal mine workings in part of King County, Washington: 

Washington Division of Geology and Earth Resources Open-File Report 83–17, 4 p., 

1 plate, scale 1:24,000.

Walsh, T.J., 1984, Geology and coal resources of central King County, Washington: 

Washington Division of Geology and Earth Resources Open-File Report 84–3, scale 

1:24,000. 

Walsh, T.J., and Lingley, W.S., Jr., 1991, Coal maturation and the natural gas potential of 

western and central Washington: Washington Division of Geology and Earth 

Resources Open-File Report 91–2, 26 p.

Warren, W.C., Norbisrath, Hans, Grivetti, R.M., and Brown, S.P., 1945, Preliminary 

geologic map and brief description of the coal fields of King County, Washington: 

U.S. Geological Survey Preliminary Map, 1 sheet, scale 1:31,680.

Weaver, C.E., 1912, A preliminary report on the Tertiary paleontology of western 

Washington: Washington Geological Survey Bulletin 15, 80 p. 

Weaver, C.E., 1916, The Tertiary formations of western Washington: Washington 

Geological Survey Bulletin 13, 327 p.

Weaver, C.E., 1937, Tertiary stratigraphy of western Washington and northwestern 

Oregon: University of Washington Publications in Geology, v. 4, 266 p.

White, C.A., 1888, On the Puget Group of Washington Territory: American Journal of 

Science, 3rd series, v. 36, p. 443–450.

Yount, J.C., Dembroff, G.R., and Barats, G.M., 1985, Map showing depth to bedrock in 

the Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF–1692, scale 1:100,000. 

Yount, J.C., and Gower, H.D., 1991, Bedrock geologic map of the Seattle 30' by 60' 

quadrangle, Washington: U.S. Geological Survey Open-File Report 91–147, scale 1:100,000.

Qvr5

Qf

m

Qw

Qmw

Qls

af

Qal

Qoal

Qp

Qvr1

Qvr2

Qvr3

Qvr4

Qvi2

Qvi1

Qvt

Qva

Qpf

Qpff

Qob

Qpog

Qpogt

Tsc

Tb

Qpo

Tv

Ti

Tpt

Tpr

9

Beta-153518

25

10

85

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3211

WASHINGTON

MAP LOCATION

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

SCALE 1:24 000

CONTOUR INTERVAL 5 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1927

1 1/2 0 1 MILE

APPROXIMATE MEAN

DECLINATION, 2012

16 / ° 1 4

MAGNETIC NORTH

TRUE NORTH

Base extracted from U.S. Geological Survey and National Ocean Service 

1:25,000-scale Digital Raster Graphic (DRG), Bellevue South, WA, 1983. Original 

1:25,000-scale published map from U.S. Geological Survey and National Ocean 

Service, 1977 (revised 1983); topography compiled from aerial photographs 

taken 1977 and field checked 1979

Shaded relief from U.S. Geological Survey 10-meter Digital Elevation Model 

(DEM), Issaquah, WA, 1983

Universal Transverse Mercator projection; North American Datum of 1927

Geology mapped by H.H. Waldron, 1956–1958; Timothy J. 

Walsh, 1980–1983, 1991; D.B. Booth, 1986 –1998, 2002–2003; 

Kathy G. Troost, 2000–2003.

GIS Database and digital cartography by Scott Shimel, 

Ralph A. Haugerud, Elizabeth A. Barnett, Matt D. Anders, 

Alison R. Duvall, Philip Dinterman, John M. Spritzer, and 

Rowland W. Tabor. Metadata by Rowland W. Tabor

Edited by Thereasa Iki 

Manuscript approved for publication May 7, 2012 

Geologic Map of the East Half of the Bellevue South 7.5' x 15' Quadrangle, Issaquah Area, King County, Washington

By

Derek B. Booth1, Timothy J. Walsh2, Kathy Goetz Troost3, and Scott A. Shimel3

2012

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not 

imply endorsement by the U.S. Government

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

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

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

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 

1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3211/

Suggested Citation: Booth, D.B., Walsh, T.J., Goetz Troost, K., and Shimel, S.A., 2012, Geologic map of 

the east half of the Bellevue South 7.5’ x 15’ quadrangle, Issaquah area, King County, Washington: 

U.S. Geological Survey Scientific Investigations Map 3211, scale 1:24,000. 

(Available at http://pubs.usgs.gov/sim/3211/.)

1 

Quaternary Research Center, University of Washington

2 

Washington Division of Geology and Earth Resources

3 

The Pacific Northwest Center for Geologic Mapping Studies,

 University of Washington