Chapter 2

Total Petroleum Systems and 

Geologic Assessment of Undiscovered 

Hydrocarbon Resources of the Western 

Oregon and Washington Province

By Michael E. Brownfield

Chapter 2 of 4

Geologic Assessment of Undiscovered Hydrocarbon Resources 

of the Western Oregon and Washington Province 

By U.S. Geological Survey Western Oregon and Washington Province Assessment Team

U.S. Geological Survey Digital Data Series DDS–69–X

U.S. Department of the Interior

U.S. Geological Survey

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Volume Title Page
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation:

Brownfield, M.E., 2011, Total Petroleum Systems and Geologic Assessment of Undiscovered Hydrocarbon Resources 

of the Western Oregon and Washington Province: U.S. Geological Survey Digital Data Series DDS–69–X, chap. 2, 

100 p.
iii

Contents

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

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

Geologic Setting of Western Oregon and Washington Province ..........................................................3

Western Oregon....................................................................................................................................5

Siletz River Volcanics..................................................................................................................5

Umpqua and Tyee Basins, Oregon Coast Range....................................................................7

Yamhill Formation.......................................................................................................................18

Cowlitz Formation ......................................................................................................................18

Spencer Formation ....................................................................................................................20

Coos Bay Basin ..........................................................................................................................21

Astoria Formation.......................................................................................................................27

Western Washington..........................................................................................................................31

Pre-Tertiary .................................................................................................................................31

Crescent Formation ...................................................................................................................31

Bellingham Basin.......................................................................................................................31

Puget Lowland............................................................................................................................35

Southern Puget Lowland ..........................................................................................................38

Olympic Peninsula Area ...........................................................................................................40

Southwestern Washington Area.............................................................................................45

Eocene Coal-Bearing Depositional Systems of Western Oregon and Washington.........................51

Tectonic Evolution of the Pacific Northwest...........................................................................................52

Cretaceous-Tertiary Composite Total Petroleum System (500401)......................................................52

Tertiary Marine Total Petroleum System (500402)..................................................................................62

Tertiary Coalbed Gas Total Petroleum System (500403) ........................................................................62

Assessment Units of Western Oregon and Washington Province......................................................68

Western Oregon and Washington Conventional Gas Assessment Unit (50040101) ................68

Tertiary Marine Gas Assessment Unit (50040201).........................................................................74

Eocene Coalbed Gas Assessment Unit (50040381) .......................................................................77

Summary........................................................................................................................................................80

Acknowledgments.......................................................................................................................................80

References Cited..........................................................................................................................................80

Appendix A....................................................................................................................................................91

Appendix B....................................................................................................................................................94

Appendix C....................................................................................................................................................97
iv

Figures

1. Map showing area of Western Oregon and Washington Province.....................................2

2. Map showing selected Tertiary basins in the Western Oregon and Washington 

Province .........................................................................................................................................4

3. Geologic map showing the major tectonic elements of the Cascadia subduction 

zone in the Pacific Northwest ....................................................................................................5

4. Geologic and tectonic features of Oregon and Washington.................................................6

5. Stratigraphic correlation chart for the northern part of western Oregon and 

western Washington showing selected Tertiary units...........................................................7

6. Geologic map of the western part of Oregon...........................................................................8

7. Geologic map of the western part of Washington and the southern part of 

Vancouver Island..........................................................................................................................9

8. Stratigraphic correlation chart for western Oregon and southern part of western 

Washington showing selected Tertiary units.........................................................................10

9. Geologic map and tectonic features of the Roseburg 1:100,000-scale 

quadrangle with oil and gas exploration wells, southwestern Oregon.............................11

10. Photograph showing outcrop of massive pillow basalt in the Paleocene to lower 

Eocene Siletz River Volcanics west of Roseburg, Oregon...................................................12

11. Photograph showing turbidite beds in the Siletz River Volcanics northwest of 

Roseburg, Oregon.......................................................................................................................12

12. Stratigraphic nomenclature chart for the southern part of the Oregon 

Coast Range.................................................................................................................................13

13. Geologic map showing the Eocene Umpqua Basin, the middle Eocene Tyee 

forarc basin, and the upper Eocene to Miocene Coos Bay Basin of the 

southern part of the Oregon Coast Range..............................................................................13

14. Diagrammatic cross sections of southern Oregon Coast Range and 

Klamath Mountains lower Eocene and upper Eocene depositional 

systems.........................................................................................................................................14

15–23. Photographs of:

 15. Conglomerate in the Bushnell Rock Formation of the Umpqua Group near 

 Lookingglass, Oregon, west of Roseburg, Oregon.......................................................15

 16. Tenmile Formation of the Umpqua Group, southern Oregon Coast Range..............16

 17. White Tail Ridge Formation of the Umpqua Group along Oregon Route 

 42 west of Roseburg, Oregon ..........................................................................................17

 18. Tyee Mountain in the southern part of the Oregon Coast Range, 

 northwest of Roseburg, Oregon.....................................................................................17

 19. Exposure of cliff-forming, thick-bedded, lithic arkosic sandstone in the 

 Baughman Member of the Tyee Formation, southern Oregon Coast Range...........18

 20. Exposure of graded medium- to fine-grained arkosic sandstone turbidites 

 with siltstone interbeds in the Tyee Formation.............................................................19

 21. Outcrop of rhythmically bedded sandstone and siltstone turbidites of 

 the Tyee Formation............................................................................................................19

 22. Outcrops of the middle to upper Eocene Yamhill Formation......................................20

 23. Exposure of the middle to upper Eocene Cowlitz Formation sandstone beds........21

24. Generalized geologic map of the Coos Bay Basin and coal field.......................................22

25. West to east cross sections across the Coos Bay Basin and coal field, 

Coos Bay Oregon ........................................................................................................................23
v

26. Stratigraphic section of Cenozoic rocks of the coastal part of the Coos 

Bay Basin, Coos Bay, Oregon...................................................................................................24

27–37. Photographs of:

27. Middle Eocene Elkton Formation in the north cove of Cape Arago 

 State Park, Oregon ............................................................................................................24

 28. Steeply dipping lower and middle members of the middle 

 Eocene Coaledo Formation..............................................................................................25

 29. Steeply dipping lower member of the middle Eocene Coaledo 

 Formation, Shore Acres State Park, Oregon, north of Cape Arago ..........................25

 30. Part of the middle Eocene lower member of the Coaledo Formation 

 at Sunset Bay, near Coos Bay, Oregon..........................................................................26

 31. Part of the middle Eocene lower member of the Coaledo Formation 

 at Sunset Bay, near Coos Bay, Oregon..........................................................................26

 32. Middle member of the middle Eocene Coaledo Formation, Sunset 

 Bay, Oregon ........................................................................................................................27

 33. Lower Miocene Nye Mudstone (base of photograph) and 

 the overlying unconformable middle Miocene Astoria Formation at 

 Nye Beach, Newport, Oregon .........................................................................................28

 34. Thick well-bedded arkosic sandstone of the middle Miocene Astoria 

 Formation at Nye Beach, Newport, Oregon..................................................................28

 35. Inclined strata of the informal Angora Peak member of the Astoria 

 Formation overlain by a Quaternary terrace.................................................................29

 36. Informal Angora Peak member of the Astoria Formation showing 

 cross-stratification in conglomerate and sandstone beds along 

 beach at Hug Point State Park north of Tillamook, Oregon........................................29

 37. Cross-stratification in the informal Angora Peak member 

 of the Astoria Formation, northern Oregon Coast Range ...........................................30

38. Generalized geologic map of northwestern Washington and southwestern 

British Columbia, Canada ..........................................................................................................32

39. Photograph of the lower to middle Eocene Crescent Formation .......................................33

40. Generalized geologic map of the Bellingham area, northwestern Washington, 

and Vancouver Island, Canada, showing rock units and major faults ..............................34

41. Generalized geologic map of the Puget Lowland area, northwestern 

Washington, showing geologic units and major faults ........................................................36

42. Photograph of the Puget Group at the Pacific Coast Coal Company’s 

John Henry No. 1 mine near Black Diamond, Washington .................................................37

43. Photograph of the Franklin No. 10A coal bed in John Henry No. 1 mine near 

Black Diamond, Washington.....................................................................................................37

44. Generalized geologic map showing the southern part of the Puget Lowland 

and the Centralia coal area, southwestern Washington .....................................................39

45. Photograph showing the Big Dirty coal bed of the Skookumchuck Formation, 

in the Hanaford pit, at the Centralia mine, west of Centralia, Washington.......................40

46. Generalized geologic map of the northern part of the Olympic Peninsula, 

Vancouver Island, Canada, and the Tofino-Juan de Fuca Basin........................................41

47. Stratigraphic column showing rocks of the Tofino-Juan de Fuca Basin, 

northwest Washington, and Vancouver Island, Canada......................................................42
vi

48. Generalized structure cross section of the Tofina-Juan de Fuca 

Basin across Strait of Juan de Fuca extending from the northern 

part of the Olympic Peninsula to the southern part of Vancouver 

Island, Canada.............................................................................................................................43

49. Generalized geologic map showing major rock units and faults on the 

Olympic Peninsula ......................................................................................................................44

50. Structure cross section showing the lower Eocene to Pliocene Olympic 

subduction complex that formed an accretionary wedge on the Olympic 

Peninsula, the Olympic peripheral rocks, and the Paleogene 

sedimentary rocks of northwestern Washington..................................................................45

51. Map showing the different core terranes and peripheral rocks on the 

Olympic Peninsula ......................................................................................................................46

52. Photograph of the upper Oligocene to middle Miocene Hoh rock assemblage 

turbidites along Beach 4, Washington coastline ..................................................................47

53. Close-up view of the upper Oligocene to middle Miocene Hoh rock 

assemblage turbidites along Beach 4, Washington coastline............................................47

54. Geologic map of southwestern Washington showing selected geologic units...............48

55. Photograph of arkosic sandstone and siltstone in the middle to upper 

Miocene Montesano Formation...............................................................................................49

56. Structure cross section across part of the inner continental shelf and 

adjacent Coast Range of southwestern Washington...........................................................50

57. Paleogeographic map showing the peat-bearing coastal plain of western 

Oregon and Washington during middle to late Eocene time...............................................51

58. Geologic provinces and paleomagnetic-rotation data of the Pacific Northwest............53

59. Continental reconstructions at 15, 37, and 50 Ma, based on paleomagnetic 

and geologic constraints...........................................................................................................54

60. Events chart for the Cretaceous-Tertiary Composite Total Petroleum System in the 

Western Oregon and Washington Province ..........................................................................55

61–63. Maps showing geology and locations of exploration wells for:

 61. Bellingham Basin area, northwestern Washington ....................................................56

 62. Puget Lowland, northwestern Washington ..................................................................57

 63. Southern part of the Puget Lowland and the Centralia and Grays 

 Harbor Basins, southwestern Washington...................................................................59

64. Burial history model for strata in the Tyee Basin..................................................................60

65–67. Maps showing the generalized geology and oil and gas data for:

65. Northern part of the Olympic Peninsula, Washington, and Vancouver 

 Island, Canada ...................................................................................................................63

 66. Northwestern Washington ..............................................................................................64

 67. Southwestern Washington and the Grays Harbor area .............................................65

68. Events chart for the Tertiary-Marine Total Petroleum System in the 

Western Oregon and Washington Province ..........................................................................66

69. Events chart for the Tertiary Coalbed Gas Total Petroleum System in the 

Western Oregon and Washington Province ..........................................................................66

70. Western Oregon and Washington Conventional Gas Assessment Unit 

located in western Oregon and Washington .........................................................................69

71. Events chart for the Western Oregon and Washington Conventional Gas 

Assessment Unit in the Western Oregon and Washington Province................................70
vii

72–74. Burial history models for strata in:

72. Northern part of the Willamette Valley..........................................................................71

 73. Southern part of the Tyee Basin .....................................................................................71

 74. General Petroleum Long Bell No. 1 well located in the central part 

 of the Tyee Basin ...............................................................................................................72

75. Northeast–southwest cross section through Reichold Energy Corporation 

Columbia County Nos. 6 and 3 wells in the Mist gas field, west of 

Portland, Oregon.........................................................................................................................73

76. Tertiary Marine Gas Assessment Unit in western Oregon and Washington....................75

77. Events chart for the Tertiary Marine Gas Assessment Unit in the 

Tertiary-Marine Total Petroleum System in the Western Oregon and 

Washington Province.................................................................................................................76

78. Eocene Coalbed Gas Assessment Unit in western Oregon and Washington..................77

79. Events chart for the Eocene Coalbed Gas Assessment Unit in the 

Tertiary Marine Total Petroleum System in the Western Oregon and 

Washington Province.................................................................................................................78

Tables

1. Oil and gas exploration wells in the Roseburg 30 x 60 quadrangle, Douglas and Coos 

Counties, Oregon ........................................................................................................................60

2. Western Oregon and Washington Province assessment results.......................................74
Abstract

The U.S. Geological Survey (USGS) recently completed 

an assessment of the undiscovered oil and gas resources of the 

Western Oregon and Washington Province, which includes 

about 40,000 mi2 in western Oregon and Washington. The 

assessment was geology based using the total petroleum system (TPS) concept. The primary geologic elements of a TPS 

include hydrocarbon source rocks (source rock maturation 

and hydrocarbon generation and migration), reservoir rocks 

(quality and distribution), and traps for hydrocarbon accumulation. Using these criteria, the USGS assessment team defined 

three TPSs, each with one assessment unit (AU): (1) the 

Cretaceous-Tertiary TPS and the Western Oregon and Washington Conventional Gas AU, (2) the Tertiary Marine TPS and 

the Tertiary Marine Gas AU, and (3) the Tertiary Coalbed Gas 

TPS and the Eocene Coalbed Gas AU. 

More than 23,000 ft of Paleogene volcanic rocks, marine 

mudstone and sandstone, and nonmarine arkosic sandstone, 

mudstone, carbonaceous shale, and coal are present in western 

Oregon and Washington. These rocks include potential mature 

petroleum source rocks and reservoir rocks.

The USGS assessed both undiscovered conventional oil 

and gas and undiscovered continuous (unconventional) gas 

in the Western Oregon and Washington Province, resulting 

in estimated mean volumes of 2,214 billion cubic feet (BCF) 

of undiscovered natural gas and 15 million barrels of oil 

(MMBO). Sixty-seven percent (1,489 BCF) of the undiscovered gas is contained within the hypothetical Eocene Coalbed 

Gas AU in western Oregon and Washington. The mean estimated volume of gas for the Western Oregon and Washington 

Conventional Gas AU is 454 billion cubic feet of gas (BCFG), 

with an estimated mean size of the largest reported gas field 

of 85 BCFG. For the Tertiary Marine AU, the estimated mean 

volume is 249 BCFG, with the estimated mean size of the 

largest expected gas field of 101 BCFG. The assessed mean 

undiscovered volume of oil in the Tertiary Marine Gas AU is 

15 million barrels of oil (MMBO), with estimated means of 

22 BCFG for associated gas and 1 million barrels of natural 

gas liquids. The mean size of the largest expected oil field is 9 

MMBO.

Introduction

As part of the U.S. Geological Survey’s (USGS) effort 

to assess the potential for undiscovered petroleum accumulations, the USGS recently conducted an assessment of the 

undiscovered oil and gas resources of the Western Oregon 

and Washington Province (fig. 1). This report supplements the 

2009 assessment (Brownfield and others, 2009) of the province by providing additional geologic detail concerning the 

defined total petroleum systems (TPS) and assessment units 

(AU), as well as a more detailed rationale for the quantitative 

assessment input.

The Western Oregon and Washington Province includes 

all of Oregon and Washington north of the Klamath Mountains 

and west of the approximate crest of the Cascade Range. The 

province extends offshore to the 3-mi limit of State waters 

on the west and to the U.S.-Canada International Boundary in the Strait of Juan de Fuca and Canada on the north. 

The province measures about 450 mi in a north–south direction and 50–160 mi east–west, encompassing approximately 

40,000 mi2 (fig. 1).

Before 1979, the only oil and gas production in the province was in Washington. In Watcom County, near Bellingham, 

Wash., small amounts of gas were produced from the Paleogene Chuckanut Formation below Quaternary gravels, and 

about 12,000 barrels of oil and associated gas were produced 

west of Aberdeen, Wash., from 1957 to 1961. Currently, the 

only hydrocarbon production is gas from the Mist field in 

northwestern Oregon (fig. 1) that was discovered in May 1979. 

The Mist field has produced about 65 billion cubic feet of gas 

(BCFG) through 2008 (Oregon Department of Geology and 

Mineral Industries, 2009).

In 1995, eight conventional plays were assessed in Province 4 by the USGS (Johnson and Tennyson, 1995): Bellingham Basin Gas Play (0401), Southeastern Puget Lowland Gas 

Play (0402), Puget Lowland Deep Gas Play (0403), TofinoFuca Basin Gas Play (0404), Western Washington Melange 

Play (0405), Southwest Washington Miocene Sandstone Play 

(0406), Cowlitz-Spencer Gas Play (0407), and Southwestern 

Oregon Eocene Gas Play (0410). Another conventional play, 

the Astoria Play (0408), was not formally assessed because 

Total Petroleum Systems and Geologic Assessment of 

Undiscovered Hydrocarbon Resources of the Western 

Oregon and Washington Province

By Michael E. Brownfield
2 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

WASHINGTON

OREGON

NEVADA

MT

IDAHO

CALIFORNIA

CANADA

Yakima

Spokane

Richland

Portland

Eugene

Columbia River

Pacific

 Ocean

Potholes 

 Reservoir

Banks 

Lake

Coeur 

d'Alene 

Lake

Lake 

Pend 

Oreille

Malheur 

Lake

Crater 

 Lake

Mist

gas field

§ ̈¦5

§ ̈¦84

§ ̈¦84

§ ̈¦82

§ ̈¦90

§ ̈¦90

P a c i f i c 

O c e a n

WA

OR

NV

MT

ID

CA

CANADA

Location map

125° 123° 121° 119° 117° 115°

42°

44°

46°

48°

50°

Coos 

Bay

Coos 

Bay

coal

field

Seattle

Bellingham

Olympic

Peninsula

Strait of 

Juan de Fuca

Grays Aberdeen

Harbor

§ ̈¦5

American

Quasar

Hickey 9–12

0 60 KILOMETERS

0 60 MILES

Figure 1. Western Oregon and Washington Province located in western Oregon 

and Washington; boundary is shown in red. Cretaceous-Tertiary Composite Total 

Petroleum System (TPS) is shown in orange. Eocene Coalbed Gas TPS is shown 

in dark blue. Tertiary-Marine TPS is shown in dark green. Eastern Oregon and 

Washington Province boundary is shown in yellow (Brownfield, 2008). Location of 

the Coos Bay coal field shown as a solid brown oval, and the Mist gas field shown 

as a solid red circle.
Geologic Setting of Western Oregon and Washington Province 3

of uncertainty about the presence of suitable reservoirs and 

source rocks. Three unconventional (coalbed gas) plays were 

also assessed, Western Washington-Bellingham Basin (0450), 

Western Washington-Western Cascade Mountains (0451), and 

Western Washington-Southern Puget Lowland (0452).

For the eight conventional petroleum plays assessed in 

Province 4 (Johnson and Tennyson, 1995), a mean undiscovered hydrocarbon resource of 590 BCFG and 19.3 million 

barrels of oil (MMBO) was estimated. Mean estimated undiscovered gas resource from the three hypothetical coalbed-gas 

plays was 697.3 BCFG.

This new assessment of the Western Oregon and Washington Province was geology based, and the total petroleum 

system (TPS) concept was applied. The geologic elements of 

a TPS include hydrocarbon source rocks (source rock maturation and hydrocarbon generation and migration), reservoir 

rocks (quality and distribution), and traps for hydrocarbon 

accumulation. Using these geologic criteria, the USGS defined 

three TPSs and two conventional assessment units (AU) and 

one continuous AU. The Cretaceous-Tertiary Composite and 

the Tertiary Marine TPSs contain the Western Oregon and 

Washington Conventional Gas and the Tertiary-Marine Gas 

AUs, respectively. The Tertiary Coalbed Gas TPS contains the 

continuous Eocene Coalbed Gas AU. Undiscovered hydrocarbon resources were assessed in each of the defined AUs.

Geologic Setting of Western Oregon 

and Washington Province

The Western Oregon and Washington Province (fig. 1) 

occupies a complex geologic setting along the northwestern continental margin of North America (figs. 2 and 3). 

The region overlies a major north-trending crustal boundary 

between the pre-Tertiary terranes of the Cascade and Klamath 

Provinces and the mafic basement of the Oregon and Washington Coast Range (Eocene Crescent Formation and Siletz 

River Volcanics). The boundary fault between these terranes is 

exposed in two places: the southern part of Vancouver Island 

where the Leach River thrust fault is the crustal boundary and 

the southwestern part of Oregon where the Wildlife Safari 

fault is the boundary (fig. 4). The eastern boundary fault likely 

is buried beneath the Puget Lowland and the Willamette Valley 

(fig. 2).

Rocks accreted during pre-Tertiary subduction crop 

out around the margins of the province in the north Cascade 

Range, San Juan Islands, and Klamath Mountains and probably underlie much of the Paleogene rocks in the eastern part 

of the province (figs. 2, 3, and 4). They include ultramafic 

rocks, mafic volcanic rocks, graywacke, mudstone, chert, and 

plutonic and metamorphic rocks and are considered unlikely 

to be prospective for hydrocarbons.

Basement rocks for the western part of the province (the 

Coast Range block) consist of a thick complex of Paleocene 

to Eocene mafic submarine volcanic rocks consisting of the 

Crescent Formation of northwestern Washington and the 

Siletz River Volcanics of the Oregon Coast Range (figs. 3 

and 4). These rocks are now widely believed to have formed 

in a continental-margin rift setting (Wells and others, 1984; 

Snavely, 1987; Babcock and others, 1992). In the Olympic 

Peninsula of western Washington, the thick submarine basalt 

of the Crescent Formation is structurally underlain by a 

subducted Eocene to Miocene melange complex consisting of 

the Ozette terrane (Snavely and others, 1993b) and the Hoh 

rock assemblage (Rau, 1973) that record ongoing subduction 

through Cenozoic time (fig. 5). Similar rocks are inferred at 

depth beneath the entire continental margin of Washington and 

Oregon.

Throughout the province, Cenozoic forearc-basin strata, 

as much as 20,000 ft thick, onlap the diverse pre-Tertiary basement and the Paleocene to Eocene volcanic basement. Forearc 

deposition occurred in a wide range of settings, including 

fluvial, fan-delta, delta, shallow-marine, continental-slope, and 

submarine-fan environments. The lower part of this sequence 

is interbedded with, and intruded by, Eocene volcanic rocks. 

The strata show general patterns of progradation northward 

from a southern Klamath igneous and metamorphic source and 

westward from both volcanic source terranes in the Cascade 

Range and distant crystalline rocks in northeastern Washington, eastern Oregon, and Idaho. Sandstones derived from the 

more distant crystalline terranes typically are Eocene in age 

and are more promising as reservoir rocks because they are 

less susceptible to diagenetic deterioration of porosity and 

permeability by alteration of unstable volcanic lithic grains. 

Such sandstone units include parts of the shallow marine 

Spencer and Cowlitz Formations, the deltaic Coaledo Formation, several members of the deltaic to submarine fan or ramp 

Tyee Formation, the fluvial Chuckanut Formation, and parts 

of the deltaic Puget Group (fig. 5; also see fig. 8). During 

the Eocene, the region was deformed by oblique subduction 

along the continental margin, as well as extension and clockwise rotation of the Coast Range block (fig. 3). This Eocene 

deformation caused widespread and heterogeneous folding, 

faulting, uplift, and subsidence. The upper middle and upper 

Eocene coal-bearing rocks crop out in the western foothills of 

the Cascade Range, on the eastern flank of the Puget Lowland, 

and in Chehalis Basin and Willamette Valley (fig. 2).

Oligocene strata generally record a westward progradation of the coastline, have a significant volcaniclastic component, and are not generally prospective for petroleum. Uplift 

of most of the Oregon Coast Range of the Oregon part of the 

forearc basin and Washington’s Olympic Mountains took place 

in Oligocene to Pliocene time, while local depositional centers 

such as the Grays Harbor Basin of southwest Washington 

continued to subside.

Formation of the Cascade volcanic arc began in the 

late Eocene to early Oligocene. Quaternary volcanoes in the 

Pacific Northwest include Mount Adams, Mount Baker, Mount 

Rainier, Mount Hood, Mount Jefferson, and the recently active 

Mount St. Helens (fig. 3).
4 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

10

10

10

10

10

10

10

10

10

15

15

15

15

15

15

15

49°

44°

124°

Klamath

Mountains

CASCADE

CASCADE RANGE

RANGE

Western Oregon and Washington

 Province boundary, approximately

 located

CANADA

15

Upper Cenozoic volcanic rocks

 and basalt flows

Mesozoic and Paleozoic 

 metamorphic and ultramafic

 rocks

Coal field Issaquah-Grand Ridge,

Green River, WilkesonCarbonado coal fields

North

Willamette

Basin

South

Willamette

Basin

Nehelem

Basin

Bellingham-Whatcom

County coal field

Bellingham Basin

Abandoned

Rattlesnake

Hills gas field

Yakima

Centralia-Chehalis

coal field

EXPLANATION

Gas (red) or oil (green) field

City

Thickness of Tertiary rocks, in

 thousands of feet

Roslyn and Manastash

coal fields

OREGON

Seattle

Seattle

Basin

Continental

margin

Wilapa

Basin

Astoria

Basin

Newport

Basin

Coos Bay

Basin

Tyee

Basin

Eugene

OLYMPIC

MOUNTAINS

Tofino-Fuca

Basin Vancouver

Island

Grays HarborOcean City

oil field

Eden Ridge

coal field

Coos Bay

coal field

UNITED STATES

WASHINGTON

Portland

Astoria

Willamette Valley

Puget

Sound

Mist

gas field

Northern Cascades

Coast Range

Coast Range

0 50 MILES

0 50 KILOMETERS

Figure 2. Locations of selected Tertiary basins in the Western Oregon and Washington Province (red outline), and the 

approximate locations of oil and gas fields and Eocene coal fields. Isopach contours of Tertiary rocks are in thousands of feet. 

Modified from Braislin and others (1971), Snavely and Wagner (1980), and Armentrout and Suek (1985).

In middle and late Miocene time, flood basalt of the 

Columbia River Basalt Group erupted in eastern Washington 

and Oregon. Huge volumes of basalt repeatedly surged down 

the course of the Columbia River, ponding in the floor of the 

northern part of the Willamette Valley and continuing on to the 

Pacific Ocean. These basalt flows built lava deltas and invaded 

the continental margin strata as voluminous sills and other 

intrusive bodies, possibly contributing to heating of potential 

petroleum source rocks in the pre-middle Miocene section.

During Miocene and Pliocene time, the ancestral Columbia River deposited large volumes of shallow marine and 

deltaic sediments in what is now coastal southwestern Washington and northwestern Oregon (Astoria and Montesano 

Formations), supplemented by smaller coastal river systems. 

Late Cenozoic deformation, continuing today, has involved 

gentle folding, rapid uplift of the Olympic Mountains, and 

both reverse and strike-slip faulting.

During the Pleistocene, alpine glaciers occupied parts 

of both the Cascade Range and the Olympic Mountains. The 

Puget Lowland, an elongate topographic trough between these 

two highlands, was occupied by a lobe of the continental ice 

sheet. The Puget Lowland is now mantled by unconsolidated 

glacial deposits of variable thickness.

Figures 6 and 7 are generalized geologic maps of the 

western parts of Oregon (modified after Walker and MacLeod, 

1991; and Walker and others, 2003) and Washington (modified 

after Schuster, 2005).
Geologic Setting of Western Oregon and Washington Province 5

Western Oregon

The western Oregon part of the province is bounded on 

the south by the northern margin of the pre-Tertiary Klamath 

Mountains and on the east by upper Eocene to Quaternary 

arc-related volcanic rocks of the Cascade Range (fig. 2) and 

extends offshore to the 3-mile limit of State waters on the 

west. The northern boundary is the Columbia River.

Siletz River Volcanics

The basement rocks of western Oregon consist of 

Paleocene to lower Eocene marine basalts and volcaniclastic 

rocks of the Siletz River Volcanics (figs. 8 and 9), which are 

as much as 19,700 ft thick (Wells and others, 2000) in the 

southern part of the Oregon Coast Range. Based on seismic 

studies (Trehu and others, 1994), the Siletz River Volcanics 

forms a continuous basement unit beneath the Oregon coastal 

region and the Willamette Valley ranging from 15.5 to 22 mi 

thick in the central part of the Coast Range; equivalent rocks 

thin to about 3.7 mi thick near Vancouver Island (Trehu and 

others, 1994). The Siletz River Volcanics, also known as the 

Siletz terrane, are thought to represent an oceanic plateau, 

an island chain, or a marginal basin that was accreted to the 

North American continent in the early Eocene (Simpson and 

Cox, 1977; Duncan, 1982; Wells and others, 1984; Clowes and 

others, 1987; Snavely, 1987; Babcock and others, 1992; Wells 

and others, 2000).

The Siletz River Volcanics, in the southern part of the 

province, consists of two submarine lithofacies. The first 

lithofacies is located mostly in the southern part of the Oregon 

Coast Range near Roseburg (figs. 3, 8, and 9), which consists of massive to pillowed basalt (fig. 10), pillow breccia, 

lapilli tuff, laminated tuff, basaltic sandstone, and mudflow 

Olympic

Peninsula

accretionary terrane

Vancouver Island

Accretionary

 complex

Siletz terrane,

 mafic crust

Quaternary

 volcanic rocks

Fault

Quaternary

 volcanoes

EXPLANATION

Thrust fault

Concealed fault

Juan de Fuca plate

Pacific plate

Gorda

plate

Explorer

plate

Cascadia

subduction zone Juan de Fuca Ridge

Mendicino fracture zone

Blanco fracture zone

CANADA

WASHINGTON

OREGON

CALIFORNIA

NEVADA IDAHO

IDAHO

Mt Rainier

Puget

Sound

Mt St. Helens Portland

R

BASIN AND RANGE

128° 124° 120° 50°

48°

46°

44°

42°

40°

Cascade

Cascade Range

Range

Seattle

MB

MA

MH

MJ

0

0 125 KILOMETERS

125 MILES

SJI

Figure 3. Generalized geologic map showing the major tectonic elements of the Cascadia subduction zone in 

the Pacific Northwest. The accretionary complex (green) broadens northward along the margin, reaching its 

widest point at the Olympic Mountains. Volcanic activity is greatest in the central part of the Cascade Range. 

MA, Mount Adams; MB, Mount Baker; MH, Mount Hood; MJ, Mount Jefferson; R, Roseburg; SJI, San Juan 

Islands. Modified after Parsons and others (2005).
6 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

breccia, with minor turbidite sandstone and mudstone (fig. 11), 

sandstone, and conglomerate interbeds (Molenaar, 1985; Wells 

and others, 2000). The turbidite interbeds contain clasts and 

rock fragments that appear to be derived from the Klamath 

Mountains, indicating that the basalts and associated volcaniclastic rocks were likely extruded near the Juan de Fuca-North 

American plate margin (fig. 3). The second lithofacies exposed 

north of Roseburg (fig. 9) consists of flow basalt and breccia 

and minor sedimentary interbeds. The age of the Siletz River 

Volcanics in the southern Oregon Coast Range is determined 

from microfauna in the sedimentary interbeds (Baldwin, 1974, 

1975; Wells and others, 2000) and the sequence was mapped 

as the Roseburg Formation (fig. 12) by Baldwin (1974).

In the type locality, in the central part of the Oregon 

Coast Range, the Siletz River Volcanics contains marine 

tholeiitic basalt flows, pillow basalt, flow breccia, and volcaniclastic rocks (Snavely and Baldwin, 1948; Beaulieu, 

1971) of early and middle Eocene age (Snavely and Wagner, 

1963; Duncan, 1982). Minor tuffaceous siltstone interbeds 

are locally present. The Kings Valley Siltstone Member of 

the Siletz River Volcanics (fig. 8) is about 3,000 ft thick and 

overlies the main volcanic unit (Vokes and others, 1955); the 

member consists of thinly bedded tuffaceous siltstone and 

Leach River fault

Wildlife Safari

fault

Metchosin

Volcanics

Crescent

Formation

Goble Volcanics

Tillamook

Volcanics

Siletz River

Volcanics

Siletz River

Volcanics

Yachats Basalt

122° 120° 118°

48°

42°

.

C h a l l i s

a x i s

Blue Mountains 

K l a m a t h

M o u n t a i n s

C a s c a d e

A r c

Columbia

River

Coast Range

WASHINGTON

OREGON

Olympic

Mountains

Vancouver

Island

Northern Cascades

Pre-Tertiary rocks

Crescent Formation and

 Siletz River Volcanics

Paleogene sedimentary

 rocks

Paleogene volcanic

 rocks 

Tyee Formation

Miocene to Oligocene

 volcanic rocks

Quaternary and Tertiary 

 volcanic rocks

EXPLANATION

Fault, ball on downthrown

 side

Thrust fault

Fold axis

0

0 100 KILOMETERS

100 MILES

Figure 4. Generalized geologic and tectonic features of Oregon and Washington. The Wildlife Safari fault is the major suture 

or boundary fault between the Oregon Coast Range terranes and the Upper Jurassic–Lower Cretaceous accretionary terranes 

in Oregon. The Leach River fault is the boundary fault between the Olympic Mountains and the Washington Coast Range 

terranes and the pre-Tertiary terranes in Washington. Modified after Wells and others (1984).
Geologic Setting of Western Oregon and Washington Province 7

water-laid tuff, and likely represents a late pyroclastic phase in 

Siletz River volcanism.

Umpqua and Tyee Basins, Oregon Coast Range

Two superimposed basins with different regional trends 

are recognized in the southern Oregon Coast Range (figs. 8, 

9, and 13) (Ryu and others, 1992; Ryu, 1995; Ryu and Niem, 

1999; Ryu, 2008). The Paleocene to early Eocene Umpqua 

Basin is northeast-trending, and is filled with strongly 

deformed turbidite rocks of the Umpqua Group (fig. 12). 

Superimposed on the Umpqua Basin is the Tyee forearc basin 

(figs. 9 and 13) (Snavely and others, 1964; Chan, 1985; Heller 

and Ryberg; 1983, Ryu and others, 1992; Ryu and Niem, 

1999; Wells and others, 2000; Ryu, 2008). The Tyee Basin is 

less deformed and filled with the lower to middle Eocene Tyee 

Formation and middle to upper Eocene Elkton, Bateman, and 

Spencer Formations (fig. 13). The lower part of this Cenozoic forearc sequence is interbedded with pillow basalt of the 

Siletz River Volcanics and intruded by Eocene volcanic rocks. 

Paleogene forearc-basin strata onlap the diverse pre-Tertiary 

basement rocks of the Klamath Mountains and the Paleocene 

to Eocene volcanic basement (fig. 13). The overall thickness 

of sedimentary rocks in the Umpqua-Tyee Basins is about 

23,000 ft in the southern part of the Oregon Coast Range 

(Ryu and Niem, 1999; Ryu, 2008). Deposition occurred in a 

range of settings, including fluvial, fan-delta, delta, shallowmarine, continental-slope, and submarine-fan environments 

(fig. 14); these strata overlap the Siletz terrane in the Oregon 

Coast Range and unconformably overlie rocks in the Klamath 

Mountains.

The Umpqua Basin strata represent a partially subducted 

accretionary wedge deposited either on a rifting continental 

margin (Wells and others, 1984) or in a trench (Heller and 

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Chuckanut

Formation

Base not exposed Base not exposed

Base not exposed

Base not

exposed Base not exposed

Base not exposed

Base not exposed

Base not

exposed

Southern Washington

Coast Range-upper

plate

Southern

Puget Sound

Central Puget LowlandWestern Cascade RangeBellingham

Basin

Tofino de

Epoch Fuca Basin

Paleocene

Clallam

Formation

Lyre

Formation

Aldwell

Formaton

Crescent

Formation

Local nonmarine

and marine

units

Boundary Bay

Formation

Blakely

Harbor

Formation

Blakeley

Formation

Renton

Formation

Tukwila

Formation

Tiger Mountain

Formation Sandstone of Scrow Bay

Raging River

Formation

Puget

Group

Ohanapecosh

Formation

Spiketon

Formation

Northcraft

Formation

Carbonado

Formation

Local

nonmarine

units

Local nonmarine units

Astoria

Formaton

Fluvial deposits

Astoria

Formaton

Skookumchuck

Formation

Cowlitz

Formation

McIntosh

Formation

McIntosh

Formation

Crescent

Formation

Crescent

Formation

Local marine

to deltaic

units

Montesano

Formation

Lincoln Creek

Formation

Lincoln Creek

Formation

Humptulips

Formation

Base not

exposed

Ozette

terrane

or melange

Hoh

rock

assemblage

or melange

Montesano

Formation

West coast

Washingtonlower plate

Twin River

Group

Quinault

Formation

Huntingdon

Formation

Northwestern

Oregon Coast Range

Troutdale Formation

Pomona Member,

Saddle Mountains Basalt

Astoria Formation

Smuggler Cove

formation (informal)

Keasey Formation

Yamhill

Formation

Siletz River

Volcanics

Base not exposed

Goble

Volcanics

Fluvial deposits

Pittsburg Bluff Formation

Cowlitz

Formation

Tillamook

Volcanics

Frenchman Springs Member,

Wanapum Basalt

Grande Ronde Basalt

Figure 5. Stratigraphic correlation chart for the northern part of western Oregon and western Washington showing selected 

Tertiary units. Light gray shading indicates intervals of erosion or nondeposition. Coal-bearing units are highlighted in green. 

Marine units containing possible source rocks are highlighted in blue. Modified after Braislin and others (1971), Armentrout 

and Suek (1985), and Johnson and others (1997).
8 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

125° 124° 123° 122°

46°

45°

44°

43°

42°

WASHINGTON

CALIFORNIA

Florence

Newport

Coos Bay

Tillamook

PACIFIC

OCEAN

Astoria

Eugene Bend

Salem

Roseburg

Drain

Portland

Grants Pass

Klamath Falls

Quaternary to Tertiary

 undifferentiated rocks 

Quaternary deposits

Tertiary rocks undivided including

 Astoria, Bateman, Cowlitz, Coaledo,

 Elkton, Eugene, and Yamhill

 Formations

Tertiary rocks undivided including

 Spencer and Tyee Formations

Umpqua Group

Tillamook Volcanics

Quaternary to Tertiary

 volcanic rocks, undifferentiated

Water

Siliez River Volcanics

 or Siletz terrane

Pre-Tertiarty rocks, undifferentiated

Tertiary intrusive rocks

Pre-Tertiary intrusive rocks

EXPLANATION

City

0 50 100 MILES

0 50 100 KILOMETERS

Figure 6. Generalized geologic map of the western part of Oregon. Modified from Walker and MacLeod 

(1991) and Walker and others (2003).
Puget Sound

Vancouver Island

OREGON

WASHINGTON

CANADA UNITED STATES

Portland

Olympia

Seattle

Bellingham

PACIFICOCEAN

Strait of Juan de Fuca Victoria

Columbia

River

GraysHarbor

WillapaBay

125° 124° 123° 122° 121°

45°48°49°47°46°

Pre-T undPale undCres MetNortNeog undQuatFaultThru uppCityTerti rocPre-T rocColu GroQuat volcWate

EXPLA

0 50 100 MILES

0 50 100 KILOMETERS

Figure 7. Generalized geologic map of the western part of Washington and the southern part of Vancouver Island. Modified after Schuster (2
10 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Bateman Formation

Umpqua Group

Siletz River

Volcanics

Tunnel Point Formation

Bastendorff Shale

Southern Oregon

Coast Range and

Coos Bay area

Base not exposed Base not exposed

Coos

Conglomerate Mbr. Empire

Formation

Tarhell Formation

Southern Willamette

Valley, central

Oregon Coast Range

Plant-bearing

tuff and associated

volcanic rocks of the

Little Butte

Volcanics

Eugene

Formation

Keasey

Formation

Fisher

Formation

Yamhill Formation

Tyee Formation

King Valley Slts. Mbr.

Siletz River

Volcanics

Coaledo Formation

Spencer Formation

Elkton Formation Tyee

Formation

Base not exposed

Southwest Washington

Coast Range

Astoria

Formation

Lincoln Creek

Formation

Crescent

Formation

Local marine

to deltaic

units

Humptulips

Formation

Northwestern

Oregon Coast Range

Northern Willamette

Valley, Oregon

Troutdale Formation Troutdale Formation

Pomona Member,

Saddle Mountains Basalt

Pomona Member, Saddle Mountains Basalt

Frenchman Springs Member,

Wanapum Basalt

Grande Ronde Basalt

Astoria Formation

Smuggler Cove

formation (informal)

Pittsburg Bluff Formation

Keasey Formation Keasey Formation

Yamhill

Formation

Siletz River

Volcanics

Base not exposed Base not exposed

Nestucca

Formation

Yamhill

Formation

Siletz River

Volcanics

Montesano

Formation

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Epoch

Paleocene

Goble

Volcanics

Fluvial deposits

Fluvial deposits Boring Lava

Scappose Formation

Pittsburg Bluff Formation

Little Butte Volcanics

Scotts Mills Formation

Sandy River Mudstone

Molalla

Formation Rhododendron

Formation

Base not exposed

Southern

Puget Sound

Local

nonmarine

units

Astoria

Formation

Lincoln Creek

Formation

McIntosh

Formation

Crescent

Formation

NorthcraftFormation

Skookumchuck

Formation Cowlitz

Formation

Spencer Cowlitz Formation

McIntosh Formation

Formation

Tillamook

Volcanics

Frenchman Springs Member,

Wanapum Basalt

Grande Ronde Basalt

Figure 8. Stratigraphic correlation chart for western Oregon and southern part of western Washington showing selected 

Tertiary units. Light gray shading indicates intervals of erosion or nondeposition. Coal-bearing units are highlighted in green. 

Marine units containing possible source rocks are highlighted in blue. Modified after Braislin and others (1971), Armentrout 

and Suek (1985), Orr and others (1992), Johnson and others (1997), and Wells and others (2000).
.

EX

W

Ty

UmSh aTuCoFaSyOiSi thWJu aJu c

123°

Jurassic arc and

sedimentary cover

Jurassic and Cretaceous

accretionary complex

Shelf and

slope deposits

Umpqua Basin

-turbidite deposits

Siletz terrane

124°

43°30’

43°00’

Tyee forearc

basin

Williams River

uplift

Turkey Hill

Turkey Hill

anticline

Oakland

anticline

Milicoma

BONANZA 

FAULT

ZONE

COOPER

RESTON

FAULT

CREEK

FAULT

Roseburg

SAFARI

WILDLIFE

FAULT

FAULT

DOTSON

BUTTE

S. Coast Range syncline

N. Coast Range

syncline

UMPQU

A

ARCH

Western Cascade Range

4 5

16

12

13

11 9

15

14

10

8

6

7 anticline

anticline

Figure 9. Generalized geologic map and tectonic features of the Roseburg 1:100,000-scale 30' × 60' quadrangle with oil and gas exploratiowells (shown in table 1), southwestern Oregon. The Wildlife Safari fault is the major suture or boundary fault between the Oregon Coast Range terranes and the Upper Jurassic-Lower Cretaceous accretionary terranes of North America. See figure 4 for the northern boundary fault on Vancouver Island. Modified after Wells and others (2000).
12 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Figure 10. Outcrop of massive pillow basalt in the Paleocene to lower Eocene Siletz River Volcanics 

west of Roseburg, Oregon (see fig. 9). Note 12-in. hammer for scale.

Figure 11. Turbidite beds in the Siletz River Volcanics northwest of Roseburg, Oregon (see fig. 9).
Geologic Setting of Western Oregon and Washington Province 13

Molenaar (1985)

Elkton Formation Elkton Formation

Baughman Member

NWUmpqua Formation

Camas Valley

 Member

54

50 

White Tail

Member

Tenmile

Bushnell Rock

Member

Flournoy

Formation

West

Southeast

North

Baldwin (1974) Diller

(1898)

Tyee

Formation Tyee Formation

Sedimentary

rocks

Umpqua

Formation

Basalt

Umpqua Formation

Umpqua Group

Diabase

Olalla Creek

Member

Ridge Member

SE

? ?

?

N

Penutian

Paleocene

Normal magnetic polarity

Reversed magnetic polarity Umpqua Group

Ulatisian

Lower

Series

Subseries Middle (part)

Chrons

Time (Ma)

Eocene

Mag. Polarity

Foram.Stage

Tenmile

 Formation

Bushnell Rock

Formation

S

?

CP13-14a?

Calcareous

nannofossils

Slater Creek

Sandstone

Member

Bateman Formation

Tyee

FM.

CP8-9

CP10

CP11

CP12a

CP12b C22n

C22r

C23n

C23r

C24r

C24n

Normal magnetic polarity sites

Reversed magnetic polarity sites

? ? ? ?

Wells and Waters

(1934)

Wells and Peck

(1961

Lookingglass

Formation

Roseburg Formation

(Basaltic rocks)

Tenmile

Member

White Tail

Ridge Member

Camas Valley

Member

Tyee Formation

Siletz River Volcanics

(Basement) Siletz River Volcanics

Bushnell Rock

Member

Wells and others (2000)

Tyee Mountain Member

Hubbard Creek Member

Camas Valley

Formation

White Tail Ridge Formation

Figure 12. Stratigraphic nomenclature chart for the southern part of the Oregon Coast Range. Modified from Wells and others (2000)

WILDLIFE

SAFARI

FAULT

Coos

Bay

Cape

Blanco

124° W 123° W

43° N

44° N

Coos

Bay

Basin

forearc basin

Basin

Umpqua

Tyee

KLAMATH

MOUNTAINS

Roseburg

Drain

Florence

General

Petroleum

Long Bell No. 1

TD-9,004 ft

Reedsport

Index Map

Western Cascade

 volcanic arc rocks

Post-Tyee undifferentiated

 strata

Spencer Formation

Bateman Formation

Elkton Formation

Tyee Formation

Umpqua Group, undivided

Siletz River Volcanics

Mesozoic strata

White Tail Ridge

 Formation

Tyee

forearc

basin

units

Umpqua

Basin

units

Fault

Thrust fault

Exploration well

EXPLANATION

0

0

10 KILOMETERS

10 MILES

Figure 13. Generalized geologic map showing 

the Eocene Umpqua Basin, the middle Eocene 

Tyee forarc basin, and the upper Eocene to 

Miocene Coos Bay Basin of the southern part of 

the Oregon Coast Range. Note the northeast–

southwest structural trend of the lower Eocene 

Umpqua Basin strata in fault contact with 

Paleocene to lower Eocene Siletz River Volcanics 

basement and Mesozoic terranes of the Klamath 

Mountains. Middle Eocene strata of the Tyee 

forearc basin and upper Eocene to middle 

Miocene strata of the Coos Bay Basin display 

a north–south trend that is discordant with the 

early Eocene trend. Modified after Ryu and others 

(1996).
Fan delta, slope, and outer shelf rocks of the Umpqua Group A, Upper Eocene B, Lower Eocene NWNW SE SE SlopeDeep-sea fan Delta Fan deltaLocal Klamath Mountains detritus Slope Deep-sea fan Laramide and volcanic detritusCascade Range Tyee Fm. Tyee Formation Klamath Mountains Subduction complex Seamount terrane Obduction and/or accretion complex Arc Klamath Mountains Forearc basin Bateman-Coaledo Formations Siletz River Volcanics Siletz River Volcanics Umpqua Group Umpqua Group Deltaic rocks of the Tyee, Coaledo and Bateman Formations

Marine volcanicsSiletz River Volcanics, also known as the Siletz terraneMetamorphic intrusive rocks

Deep-sea fanSlope and outer shelf rocks of the Tyee FormationSlope rocks

EXPLANATION

INDEX M

Line of cross

section

124°

48°40°

Oregon Coast  Range

Cascadia

subduction zone

Mendicino fracture zone

EXPLANATION

CALIFORNIA

Plutonic belts

C

a

s

c

a

d

e

a

rc

Klamath Mtns.

Metamorphic terranes

00 100 KILOMETERS

100 MILES

Figure 14. Diagrammatic cross sections of southern Oregon Coast Range and Klamath Mountains lower Eocene and upper Eocene depositional syshowing (A) subduction-zone sedimentation during accretion of the Siletz River Volcanics and (B) post-accretion forearc sedimentation. Modified aand Ryberg (1983) using the Eocene stratigraphy revisions of Molenaar (1985) and Wells and others (2000).
Geologic Setting of Western Oregon and Washington Province 15

Ryberg, 1983).The stratigraphic nomenclature has undergone 

many changes from the late 1890s (fig. 12), with both the 

Umpqua Formation and the Umpqua Group names being used; 

this paper adopts the stratigraphic nomenclature of Wells and 

others (2000) as shown in the left-hand column of figure 12. 

The Umpqua Group is at least 10,000 ft thick (Molenaar, 

1985). Syntectonic fan-delta and marginal-marine lithic sediments were deposited along the southernmost margin of the 

Oregon Coast Range as the Bushnell Rock Formation of the 

Umpqua Group (Wells and others, 2001) and the Slater Creek 

Sandstone Member of the Bushnell Rock Formation (figs. 12 

and 15). The Bushnell Rock Formation consists mostly of 

conglomerate (fig. 15), consisting of boulder to pebble clasts 

derived from the Klamath Mountains. Depositional environments include fanglomerate, fan delta, and deep marine 

turbidite channels that interfinger upsection with thick-bedded, 

fine-grained sandstone of the Slater Creek Sandstone Member. 

Overlying the Bushnell Formation and Slater Creek Member 

is the Tenmile Formation (fig. 12), which has been interpreted 

as trench-fill turbidites deposited on the Siletz River Volcanics. 

The transgressive Tenmile Formation consists of deep-marine 

inner, middle, and outer submarine-fan turbidite sandstones 

(fig. 16) and basinal mudstones in a marginal basin or trench 

setting (Heller and Ryberg, 1983; Niem and Niem, 1990; Ryu 

and Niem, 1999; Wells and others, 2000). Subduction ceased 

along the trench after the deposition of the Tenmile Formation resulting in development of seamounts. The fluvial to 

deltaic lithic strata of the overlying White Tail Ridge Formation (fig. 17) filled irregular lows between the seamounts and 

thinned over submarine highs (Ryu and Niem, 1999). The 

White Tail Ridge locally contains carbonaceous mudstones 

and coal. The uppermost formation of the Umpqua Group is 

the Camas Valley Formation (fig. 12), which consists of thick, 

concretionary, foraminifer-bearing dark-gray mudstone that 

was deposited in a slope environment.

West of the Roseburg area and east and south of the 

Coos Bay Basin in the Oregon Coast Range (figs. 6 and 13), 

the Umpqua Group cannot be differentiated into individual 

formations (Molenaar, 1985). South of Coos Bay Basin, the 

sequence consists of thick mudstone and turbidites, and west 

and north of Coos Bay, it is absent due to depositional thinning 

across structural highs or seamounts within the Siletz terrane.

The Eocene Tyee forearc basin extends north–south about 

200 mi and is overlapped on the east by Tertiary volcanic 

rocks of the Cascade Range and bounded on the south by 

the Mesozoic Klamath Mountains (figs. 6 and 13). The basin 

contains about 23,000 ft of strata deposited in the active 

North American convergent margin (Ryu, 2003) and records 

a change from the Umpqua Group in deformation style and 

provenance. During the late early Eocene, a new subduction 

zone developed west of the present continental margin forming a magmatic arc in central Oregon west of the Blue Mountains where the volcanic rocks of the Clarno Formation were 

deposited (see index map, fig. 14). Arkosic and volcaniclasic 

sediments from the Idaho batholith and Clarno volcanic arc 

were deposited in the Tyee forearc basin (Heller and Ryberg, 

1983).

In the southern part of the Tyee Basin, the lower to middle Eocene Tyee Formation (fig. 12) is about 10,000 ft thick 

and is subdivided into three members in the southern Oregon 

Coast Range: the Tyee Mountain, Hubbard Creek and Baughman Members (Ryu and others, 1996; Wells and others, 2000). 

The Tyee Mountain Member (fig. 18) ranges in thickness from 

about 3,000 to 6,560 ft and consists of thick, fine-grained, 

micaceous, rhythmically bedded sandstone; lithic arkosic 

sandstone; and mudstones deposited as turbidites in a forearc 

basin (Heller and Ryberg, 1983). The Hubbard Creek Member, 600 to 1,600 ft thick, consists of thin-bedded, 

micaceous, gray siltstone and turbidite channel sandstones that have been interpreted as slope deposits 

(Ryu and others, 1992). The deltaic to fluvial Baughman Member (fig. 19) is a thick-bedded, micaceous, 

crossbedded arkosic sandstone and gray mudstone 

ranging in thickness from 2,000 to 2,500 ft (Baldwin, 

1974; Ryu and others, 1996) and contains three to 

four thickening-upward cycles in the deltaic facies 

(Wells and others, 2000). The Baughman Member 

contains minor carbonaceous mudstone and coal.

In the central, northern, and western parts of 

the Tyee Basin, the Tyee Mountain and Baughman 

Members cannot be differentiated where the intervening Hubbard Creek Member is missing; in those 

areas, the Tyee Formation is recognized only as a 

single unit (fig 12). The Tyee turbidites northeast of 

Newport, Oreg., are observed in outcrop as either 

thick-bedded, graded, medium- to fine-grained lithic 

arkosic turbidite sandstones (fig. 20) or as more 

distal rhythmically bedded turbidites consisting of 

sandstone and mudstone units (fig. 21).

Figure 15. Outcrop of conglomerate in the Bushnell Rock Formation of the 

Umpqua Group (see fig. 12) near Lookingglass, Oregon, west of Roseburg, 

Oregon (see fig. 9). Note 3.25-in. knife for scale.
16 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Figure 16. Outcrop images of the Tenmile Formation of the Umpqua Group (see fig. 12), southern 

Oregon Coast Range. A, Outcrop of strongly folded turbidite beds in the Tenmile Formation northwest 

of Roseburg, Oregon (see fig. 9). B, Strongly folded turbidite beds in the Tenmile Formation along the 

Umpqua River northwest of Roseburg, Oregon (see fig. 9).

A

B
Figure 17. Outcrop of the White Tail Ridge Formation of the Umpqua Group (see fig. 12) 

along Oregon Route 42 west of Roseburg, Oregon (see figure 9).

Figure 18. Tyee Mountain in the southern part of the Oregon Coast Range, northwest 

of Roseburg, Oregon (see figs. 6 and 9). Massive cliff-forming sandstone units are 

turbidites in the Tyee Mountain Member of the Tyee Formation (see fig. 12).

Geologic Setting of Western Oregon and Washington Province 17
18 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Overlying the Tyee Formation is the middle Eocene 

Elkton Formation (fig. 12), consisting of up to 1,600 ft of 

mudstone that was deposited in a slope environment (Ryu and 

Niem, 1999; Ryu, 2003). The Elkton Formation interfingers 

with the underlying Baughman Member of the Tyee Formation 

in the Roseburg area (Wells and others, 2000), and is overlain 

by the middle and upper Eocene wave- to tide-dominated 

deltaic Bateman Formation (fig. 8). The Bateman Formation 

contains delta-front, distributary mouth bar, and distributary 

channel units. The delta-front facies ranges from 100 to 200 ft 

thick and consists of micaceous feldspathic sandstone with 

interbeds of burrowed siltstone and carbonaceous mudstone 

and coal (Ryu and others, 1992; Ryu, 2008).

Yamhill Formation

The middle to upper Eocene Yamhill Formation unconformably overlies the Siletz River Volcanics in the northcentral Oregon Coast Range (fig. 8); it is interbedded with 

the upper middle Eocene Tillamook Volcanics (Wells and 

others, 1994) and overlies and might be interbedded with Tyee 

Formation. Baldwin and others (1955) reported a thickness as 

much as 6,500 ft at the type locality along Mill Creek in the 

Sheridan, Oregon, 1:62,500-scale quadrangle (Baldwin and 

others, 1955). The Yamhill Formation (fig. 22) ranges from 

3,000 to about 5,000 ft thick west of Salem, Oreg. (fig. 6), in 

the Sheridan and Grand Ronde 1:24,000-scale quadrangles, 

where it consists of massive to thin-bedded concretionary 

marine siltstone and thin interbeds of arkosic, glauconitic, and 

basaltic sandstone and, locally, contains interbedded basalt 

lava flows and lapilli tuff (Brownfield, 1982a,b). In the northern part of the Coast Range, thicknesses range from 1,000 to 

2,000 ft. The basal part of the Yamhill Formation in the Dallas 

quadrangle, west of Salem, Oreg. (fig. 6), consists locally of 

impure shallow-water limestone beds, 40 to 100 ft thick (Baldwin, 1964; Boggs and others, 1973), which form a unit named 

the Rickreall Limestone Member of the Yamhill Formation by 

Baldwin (1964). In the northwestern part of the Oregon Coast 

Range, the upper part of the Yamhill Formation is basaltic and 

interfingers with basalt breccia and sandstone of the Tillamook 

Volcanics (fig. 5) (Wells and others, 1994). Foraminiferal 

assemblages in siltstone are representative of the Ulatisian 

and lower part of the Narizian Stages of the middle Eocene 

(Snavely and others, 1969; McNeal, 1980).

Cowlitz Formation

The Cowlitz Formation, of middle to late Eocene age, 

unconformably overlies the Yamhill Formation and the Tillamook Volcanics in the northern part of the Oregon Coast 

Range (fig. 5) (Armentrout and Suek, 1985). The type locality 

for the Cowlitz Formation, first described by Weaver (1912), 

is located in southwestern Washington where it consists of 

about 4,200 ft of marine, brackish-water, and nonmarine rocks 

with minor coal (Weaver, 1937). In northwestern Oregon, the 

Cowlitz Formation consists of as much as 1,000 ft of crossbedded, micaceous, carbonaceous, fine- to medium-grained 

arkose and lithic arkose (fig. 23) with minor conglomerate, 

mudstone, and siltstone and is locally concretionary. Laminated thin-bedded mudstone and siltstone are interbedded in 

the upper part with minor volcanic flows, breccia, and tuffs . 

The Cowlitz Formation was deposited along a broad coastal 

plain and shelf margin that extended from Coos Bay in the 

south to Bellingham in the north (Dott, 1966; Buckovic, 1979; 

Figure 19. Exposure of cliff-forming, 

thick-bedded, lithic arkosic sandstone 

in the Baughman Member of the Tyee 

Formation (see fig. 12), southern Oregon 

Coast Range in road cut along Oregon 

Route 42 west of Roseburg, Oregon (see 

figs. 6 and 9).
Geologic Setting of Western Oregon and Washington Province 19

Figure 20. Exposure of graded mediumto fine-grained arkosic sandstone 

turbidites with siltstone interbeds in the 

Tyee Formation in road cut along U. S. 

Route 20 east of Newport, Oregon (see fig. 

6). Sandstone beds are 2 to 5 ft thick and 

the siltstone beds are 0.5 to 2 ft thick.

Figure 21. Outcrop of 

rhythmically bedded sandstone 

and siltstone turbidites of the 

Tyee Formation in road cut along 

U. S. Route 20 east of Newport, 

Oregon (see fig. 6)
20 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Johnson, 1984a; Armentrout and Suek, 1985). The arkosic 

sands were transported from the east by river systems from 

the Idaho batholith of eastern Oregon and Washington. Local 

volcanic islands contributed the volcanic rock fragments to the 

sandstones. The interbedded volcanics are referred to as the 

Goble Volcanics (fig. 5) (Wilkinson and others, 1946; Alger, 

1985); the upper part of the Tillamook Volcanics was added 

to this unit by Baldwin and others (1955). At the Mist field, 

Oregon’s only producing gas field, the producing zones are in 

the shallow marine sandstone of the Cowlitz Formation. Newton and Van Atta (1976) reported that the Cowlitz foraminiferal assemblages are assigned to the upper part of the Narizian 

Stage of Mallory (1959).

Spencer Formation

The middle to upper Eocene Spencer Formation (figs. 

6 and 8) crops out along the west side of the Oregon Coast 

Range from about 20 mi southwest of Portland to the Roseburg area where it unconformably overlies the Umpqua Group 

and is overlain by Cascade Range volcanic rocks (fig. 13) 

(Wells and others, 2000). In the central part of the Oregon 

Coast Range, the Spencer Formation unconformably overlies 

the Yamhill Formation (fig. 8) and in places is unconformably 

on the Tyee Formation (Beaulieu, 1971). The Spencer Formation consists of micaceous arkosic sandstone, carbonaceous 

siltstone and mudstone, and lignite and subbituminous coal. 

Figure 22. Outcrops of the middle 

to upper Eocene Yamhill Formation. 

A, Exposure of Yamhill overlain by 

volcanic rocks of the upper Eocene 

Nestucca Formation west of Salem, 

Oregon (see fig. 6). Photograph 

courtesy of Alan S. Niem. B, Exposure 

of Yamhill overlain by the upper 

Eocene Nestucca Formation (above 

12-in. hammer) west of Salem, Oregon 

(see fig. 6).

A

B
Geologic Setting of Western Oregon and Washington Province 21

Van Atta (1986) divided the Spencer Formation into two informal members, a lower member consisting of 800 to 1,000 ft 

of arkosic lithic sandstone and an upper member of siltstone 

and mudstone ranging in thickness from 1,000 to 1,300 ft; 

deposition occurred in neritic, nearshore, and nonmarine environments (Van Atta, 1986; Van Atta and Thoms, 1993). The 

Spencer Formation is 980 ft thick in the Roseburg area (Wells 

and others, 2000) and thickens to about 4,500 ft northwest of 

Eugene (Beaulieu, 1971) (figs. 6 and 8). In the northwestern 

part of the Willamette Valley, the sandy part of the Spencer is 

about 200 ft thick and is interbedded with mudstone and minor 

carbonaceous shale and coal (Schlicker, 1962); it then wedges 

out southwest of Portland (Beaulieu, 1971). The sandstones 

contain about 55 percent feldspar and about 45 percent quartz. 

The Spencer Formation is assumed to be widespread under the 

younger rocks of the Willamette Valley and to be equivalent to 

the upper part of the Cowlitz Formation, or slightly younger 

than the Bateman and Coaledo Formations.

Coos Bay Basin

The Coos Bay Basin is located in the southwestern part 

of the Oregon Coast Range (figs. 24 and 25). The basin is a 

roughly elliptical structural basin measuring approximately 35 

mi north–south and about 11 mi east–west (fig. 24). More than 

12,000 ft of sedimentary rocks were deposited in the basin 

beginning in the early Eocene and ending in the Pleistocene 

(fig. 26).

The oldest rocks exposed in the coastal part of the Coos 

Bay Basin are in the middle Eocene Elkton Formation (figs. 8, 

12, and 27), which crops out in the sea cliffs at Cape Arago 

(fig. 24). Overlying the Elkton Formation is more than 6,000 ft 

of coal-bearing rocks of the middle Eocene Coaledo Formation. The Coaledo Formation, which is present only in the 

complex structural Coos Bay Basin (fig. 25), was divided into 

three informal members by Allen and Baldwin (1944). The 

lower member of the Coaledo Formation (figs. 26, 28, and 

29) consists of tuffaceous sandstone with minor conglomerate, pebbly sandstone, siltstone, carbonaceous mudstone, and 

coal deposited in a deltaic environment; thickness ranges from 

1,700 to at least 1,900 ft (Allen and Baldwin, 1944; Baldwin 

and others, 1973; Armentrout, 1980). Excellent exposures of 

cross bedding, large load structures (flame structures), and 

sole markings can be seen at Sunset Bay (figs. 30 and 31). The 

middle member of the Coaledo Formation (figs. 26 and 32) is 

mostly thin-bedded siltstone with minor thin beds of sandstone 

and tuff deposited during a maximum transgression event 

and is at least 2,940 ft thick (Armentrout, 1980). The upper 

member of the Coaledo Formation (fig. 26) is characterized by 

regression and the return to a deltaic environment from deeper 

Figure 23. Exposure of the middle to upper Eocene Cowlitz Formation sandstone beds in road cut 

along U.S. Route 26 west of Portland, Oregon. The Mist gas field produces gas from Cowlitz Formation 

reservoirs (see fig. 1).
22 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Pacific Ocean

Coos

Bay Coos Bay

Haynes

Inlet

Tenmile

Lake

North Tenmile

Lake

Eel Lake

Clear

Lake Lake Edna

U

U

U D

D

D

U

U

U

D D

U

U D

D U

D

D

FAULT

LILLIAN

WESTPORT

ARCH

(WEST)

South

Sough

syncline

THREEMILE

CREEK

FAULT 

Beaver

Slough

ISTHMUS SLOUGH FAULT

Summer

syncline

CHINA

CAMP

CREEK

FAULT

Norway

anticline

Beaver

Slough

syncline

Pulaski Fishtrap

Creek

syncline

anticline

Hall

Creek

syncline

B

B'

A

A'

Cape Arago

anticline

CAPE

ARAGO

Sunset

Bay

River

Coquille

Coos Bay

BLUE MOUNTAIN FAULT

syncline

Catching

Slough

Coaledo

anticline

South

Slough

OREGON

Portland

Coos Bay

Klamath Falls

Eugene Bend

Salem

Pendleton

Baker

La Grande

Coos Bay Basin

EXPLANATION

Extensive Quaternary surficial deposits

 covering Coaledo Formation contacts

Upper member, coal-bearing (includes

 overlying Bastendorff Shale and

 Empire Formation along synclinal axes)

Coaledo Formation (Eocene),

 undivided (north of Coos Bay)

Middle member, noncoal-bearing

Lower member, coal-bearing

Axis of anticline

Axis of syncline

Thrust fault

Normal, reverse fault

Coal mine or exploration borehole

Dry hole, show of gas

Dry hole, show of gas and oil

Dry hole

Pre-Coaledo Formation rocks

 (includes Umpqua Group)

Coalbed-methane core hole

Coaledo

Formation

0 5 KILOMETERS

0 5 MILES

0 100

0 100 200 KILOMETERS

200 MILES

Figure 24. Generalized geologic map of the Coos Bay Basin and coal field. A–A’ and B–B’ are lines of cross 

section shown on figure 25. Modified after Baldwin and others (1973).
0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

Vertical exaggeration: 133%

A

B B'

BIG CREEK MINE

ELEV (ft)

2,0001,000

-1,000-2,000

0 (sea level)

ELEV (ft)

2,0001,000

-1,000-2,000

0 (sea level)

Cape Arago

CAPE ARAGOANTICLINE AND FAULT

Big Creek

Coquille River Hatcher Slough Iowa Slough Fat Elk Creek Pulaski

anticline

Hall Creeksyncline

Beaver Slough syncline

Coquille River

Coquille River

Haywood Creek

South Slough syncline

South

Slough Davis

Slough

Isthmus

Slough

Beaver Slough

syncline

Catching Slough

Coaledo anticline

Catching 

Slough

Sumsync

ISTHMUS SLOUGH

FAULT

Newport

syncline

Westport

arch

(West)

Westport

arch

(East) ? ? 

Davis Slough coals 36-COAL MINE Summer coals Summ

MAXWELLMINE

THOMASMINE

NW ExplorationWestport #1

PhillipsDobbyns

Q Q Q Q Q Q Q

Pεcl Pεcm Pεcu Peb

Pεtp

Nm Pεb Pεcu Pεcm Pεcu Pεb Pεcm Pεcl Pεcm Pεcu Pεcu Pεb

Pεsr

Pεu 

Pεcl

Pεcl

Pεsr

Npe Pεcl

Pεsr ?

Geological interpretation adapted from Baldwin and others (1973) and Baldwin (1966)

Geological interpretation adapted from Baldwin and others (1973).Structural trends illustrated for Siletz River Volcanics are diagrammatic only.

Structural trends illustrated for Siletz River Vollcanics are diagrammatic only.

Donaldson prospect RIVERTON MINE

Coast Oil Well #2

LYONS MINE

NW Exploration Fat Elk #1

Coast Oil Well #3

Coast Oil Well #4

Coast Oil Fat Elk #1

SCORBY-MCGINTY

SMITH-KAY MINE

EUREKA MINE

Q Q

Q

Q Q Q

ELEV (ft)

2,0001,000-1,000-2,0000 (sea level)

TD 2,526

TD 3,692

TD 6,941

TD 1,640 TD 1,640

TD 3,117

TD 2,255

Pεsr Pεcl

Pεcm

Pεcu

Pεsr

Pεcl

Pεcm

Pεsr Pεsr

?

? ?

?

Fault

Axis of anticlinAxis of syncline

Coal mine or exPetroleum expl

Dry holeDry hole, show 

Neogene (Miocene) 

Paleogene (Eocene) U

Empire FormatiSedimentary roTunnel Point SaUmpqua Group  Baldwin, 1974Siletz River Vol Roseburg Form

Upper membMiddle memLower memb

Bastendorff ShaQuaternary surfCoaledo Forma

EXPLANATI

Npe

Pεtp

Pεcu

Pεcm

Pεcl

Pεu

Pεsr

Pεb

Nm

Q

Figure 25. West to east cross sections across the Coos Bay Basin and coal field, Coos Bay Oregon. Location of cross section shown in figure 24. Baldwin and others (1973).
24 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Pleistocene

Late

Miocene

Late early and

middle Miocene

Late

Eocene

Middle

Eocene

Early

Eocene

Terrace deposits

Empire

Formation

1,600 ft

Tunnel Point

Formation, 760 ft

Miocene beds

300 ft (?)

Bastendorff

Formation

2,900 ft

Upper Coaledo

Formation

1,370 ft

Middle Coaledo

Formation

2,940 ft

Lower Coaledo

Formation

1,700 ft

Elkton

Formation

>1,000 ft ?

? ? ? ?

0’

1,000’

2,000’

4,000’

3,000’

5,000’

6,000’

7,000’

8,000’

9,000’

10,000’

11,000’

12,000’

?

NESS

THICK- AGE UNIT LITHOLOGY

Conglomerate

Sandstone

Nonmarine rocks

including coal

Marine and marginal

marine rocks

EXPLANATION

Figure 26. Stratigraphic section of Cenozoic rocks 

of the coastal part of the Coos Bay Basin, Coos Bay, 

Oregon. Modified after Armentrout (1980).

Figure 27. Outcrop of the middle 

Eocene Elkton Formation in the north 

cove of Cape Arago State Park, Oregon 

(see fig. 24).
Geologic Setting of Western Oregon and Washington Provnice 25

Figure 28. Outcrop of the 

steeply dipping lower and 

middle members of the 

middle Eocene Coaledo 

Formation; view is north 

across Sunset Bay (see fig. 

24). Middle member of the 

Coaledo is only exposed in 

the cliff on the far right of the 

photograph. The strata dip 

eastward toward the trough 

of the South Slough syncline 

in the Coos Bay coal field.

Figure 29. Outcrop of 

the steeply dipping lower 

member of the middle 

Eocene Coaledo Formation 

(see fig. 24), Shore Acres 

State Park, Oregon, north of 

Cape Arago (see fig. 24).
26 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Figure 30. Outcrop of 

part of the middle Eocene 

lower member of the 

Coaledo Formation at 

Sunset Bay, near Coos 

Bay, Oregon (see fig. 24). 

Large load structures 

(flame structures) can be 

seen in the center of the 

photograph.

Figure 31. Outcrop of 

part of the middle Eocene 

lower member of the 

Coaledo Formation at 

Sunset Bay, near Coos 

Bay, Oregon (see fig. 24). 

Hummocky and swaley(?) 

cross-stratification can be 

seen in the center of the 

photograph.
Geologic Setting of Western Oregon and Washington Province 27

marine environments and consists of tuffaceous sandstone 

with minor beds of siltstone, carbonaceous mudstone, and coal 

with thicknesses ranging from 2,300 to 2,900 ft (Baldwin and 

others, 1973; Armentrout, 1980).

Astoria Formation

Rocks assigned to the lower to middle Miocene Astoria 

Formation (figs. 5, 6, and 8) crop out in the northernmost 

part of the Oregon Coast Range along the lower Columbia 

River (figs. 1 and 2) and along the northern Oregon coast in 

a series of embayments from Newport to Astoria (fig. 6). The 

stratigraphic definition of the Astoria Formation varies in the 

different mapped areas in northwestern Oregon because the 

correlation with the type area has been on a faunal basis and 

not on the basis of lithology or continuous mapping into the 

type area.

The Astoria Formation was first described by Dana 

(1849) for exposures in Astoria, Oreg. Howe (1926) informally divided the Astoria into three members: (1) a lower 

unit, about 150 ft thick, consisting of yellow to gray, massive 

to cross-bedded, medium- to fine-grained, arkosic sandstone 

interbedded with mudstone; (2) a middle unit consisting of at 

Figure 32. Outcrop of the middle member of the middle Eocene Coaledo Formation, Sunset Bay, 

Oregon (see fig. 24).

least 1,000 ft of mudstone and interbedded thin glauconitic 

sandstone; and (3) an upper unit characterized by several 

massive to cross-bedded arkosic sandstone beds ranging in 

thickness from 10 to 100 ft. Most of the original exposures 

described by Howe (1926) are now obscured by man-made 

structures or by sand dredged from the Columbia River.

In the Newport area, about 100 mi south of Astoria 

(fig. 6), the stratigraphic relations of the Astoria Formation are 

more clearly defined (Vokes and others, 1949; Snavely and 

others, 1969). About 2,000 ft of Astoria Formation crops out in 

the Newport embayment, where it unconformably overlies the 

lower Miocene Nye Mudstone (fig. 33) and the upper Oligocene Yaquina Formation and is unconformably overlain by 

the middle Miocene basalt of Depoe Bay. The Astoria Formation consists mostly of shallow marine arkosic and micaceous 

sandstone (fig. 34) and carbonaceous siltstone.

The Astoria Formation in the northern part of the Oregon 

Coast Range has been divided into four informal members by 

Niem and Niem (1985): the deltaic to marginal marine Angora 

Peak, the shallow marine Wickiup Mountain, the submarine 

channel and fan Youngs Bay, and the turbidite Cannon Beach. 

The Angora Peak member (figs. 35–37), ranging in thickness 

from about 200 ft to more than 800 ft, consists of thick bedded 
28 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Figure 33. Outcrop of the lower Miocene Nye Mudstone (base of photograph) and the overlying 

unconformable middle Miocene Astoria Formation at Nye Beach, Newport, Oregon (see fig. 6).

Figure 34. Outcrop of thick well-bedded arkosic sandstone of the middle Miocene Astoria 

Formation at Nye Beach, Newport, Oregon (see fig. 6)
Geologic Setting of Western Oregon and Washington Province 29

Figure 35. Outcrop of the inclined strata of the informal Angora Peak member of the Astoria 

Formation overlain by a Quaternary terrace. Outcrop north of Otter Crest State Park, north of 

Newport, Oregon (see fig. 6).

Figure 36. Outcrop of the informal Angora Peak member of the Astoria Formation showing 

cross-stratification in conglomerate and sandstone beds along beach at Hug Point State Park 

north of Tillamook, Oregon (see fig. 6).
30 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Figure 37. Close-up images of cross-stratification in the informal Angora Peak member of the 

Astoria Formation, northern Oregon Coast Range. A, Outcrop of the Angora Peak member showing 

planar and trough cross-stratification in conglomerate and sandstone beds along beach at Hug 

Point State Park north of Tillamook, Oregon (see fig. 6). B, Outcrop of the Angora Peak member 

showing detail of the cross-stratification in conglomerate and sandstone beds along beach at Hug 

Point State Park north of Tillamook, Oregon (see fig. 6). Note 3-in. knife for scale.

A

B
Geologic Setting of Western Oregon and Washington Province 31

and laminated arkosic sandstone and lithic sandstone with 

minor conglomerate, mudstone, and thin coals. The Wickiup 

Mountain member is characterized by as much as 1,300 ft of 

structureless to laminated shallow-water arkosic sandstone and 

minor mudstone capped by glauconitic sandstone. The Youngs 

Bay member is mostly deep-marine mudstone as much as 

2,200 ft thick, interbedded with two lenticular, medium- to 

coarse-grained arkosic sandstone units, 200 and 1,000 ft thick, 

respectively. The Cannon Beach member ranges in thickness 

from about 2,000 ft in the Tillamook area (Wells and others, 

1994) to several thousand feet near Astoria (fig. 6) (Niem 

and Niem, 1985), and consists of well-bedded siltstone and 

mudstone with minor amounts of rhythmically bedded, graded 

arkosic sandstone.

Western Washington

The western Washington part of the Western Oregon 

and Washington Province (figs. 3 and 4) occupies a complex 

geologic setting along the northwestern continental margin 

of North America and is bounded on the north by the International Boundary in the Straits of Juan de Fuca and San Juan 

Islands (fig. 3). It extends offshore to the 3-mi limit of State 

waters on the west and on the east by the approximate crest of 

the Cascade Range. The region overlies a major north-trending 

crustal boundary between basement rocks of the pre-Tertiary 

Northern Cascade Range and Cascade arc to the east and the 

Eocene Coast Range to the west (figs. 2, 4, and 38). The Puget 

fault, also known as the Coast Range boundary fault (Johnson 

and others, 1996), is mostly buried by Quaternary deposits in 

the Puget Lowland (fig. 38; also see fig. 41).

Pre-Tertiary

Pre-Tertiary basement rocks of the Northern Cascades 

include diverse metamorphic, igneous, and sedimentary rocks 

that form several distinct crustal terranes with allochthonous 

and (or) exotic origins (figs. 4, 7, and 38). The final stages 

of accretion of these crustal terranes were completed by the 

Late Cretaceous, after which these rocks formed the stable 

platform of the Washington continental margin. During the 

early to early middle Eocene, the eastern pre-Tertiary basement underwent significant dextral strike-slip faulting and 

transtensional deformation. This deformation was manifested 

by the formation of rapidly subsiding sedimentary basins with 

common intrabasinal volcanic centers and uplift and (or) igneous intrusion of the crystalline rocks (Johnson, 1985). Eocene 

sedimentary rocks within these basins are as thick as 20,000 ft 

and constitute some of the thickest nonmarine successions in 

North America (Johnson, 1985).

Crescent Formation

The basement rocks of the Washington Coast Range 

consist of lower and lower middle Eocene marine basalts and 

volcaniclastic rocks of the Crescent Formation, which was 

named for Port Crescent on the south shore of Strait of Juan 

de Fuca, west of Port Angeles, Wash. (figs. 4, 5, 7, and 38). 

The Crescent Formation (fig. 39) consists of massive pillow 

and diabasic basalt flows, flow- and tuff-breccia, and tuff with 

interbedded basaltic conglomerate and sandstone, and wellindurated, massive tuffaceous siltstone, argillite, and minor 

limestone (Brown and others, 1960; Cady and others, 1972; 

Wolfe and McKee, 1968, 1972; Whetten and others, 1988). In 

the Tofino-Fuca Basin (fig. 5), the Crescent Formation underlies and interfingers with the Aldwell Formation (see fig. 47). 

The Crescent Formation is in part equivalent to the Siletz 

River Volcanics of Oregon and may be as much as 25,000 ft 

thick (Rau, 1964). These rocks are now widely believed to 

have formed in a continental-margin rift setting (Wells and 

others, 1984; Snavely, 1987; Babcock and others, 1992).

Post-rift subsidence of the Washington Coast Range is 

thought to be of thermal origin (Johnson and Yount, 1992). 

Johnson (1984c, 1985) and Johnson and others (1994, 1996) 

suggested that the eastern margin of this rifted terrain is 

coincident with the dextral strike-slip Puget fault (fig. 38). 

Northward motion of the Coast Range block along the Puget 

fault was accommodated to the north by south-directed thrusting on southern Vancouver Island (Clowes and others, 1987), 

and folding and faulting within the Coast Range block in the 

Straits of Juan de Fuca and on the northern Olympic Peninsula 

(Snavely, 1987). Johnson (1984c, 1985) suggested that most 

strike-slip motion on the crustal boundary occurred prior to 

the late Eocene, after which strike-slip motion diminished 

and was distributed on several fault zones in the southeastern 

Puget Lowland (Johnson and others, 1994). The Puget fault is 

covered by upper Eocene and higher strata and is located and 

delineated mainly with geophysical data.

Bellingham Basin

The Eocene Chuckanut Formation (Johnson, 1982; Johnson, 1984a) of the Bellingham Basin area of northwest Washington consists of alluvial strata as much as 19,690 ft thick, 

one of the thickest nonmarine sequences in North America 

(figs. 5, 38, and 40). The Chuckanut is present in several 

structurally low outcrop belts, located west of Mount Baker in 

the Northern Cascades. These outcrop belts are remnants of a 

much larger Eocene fluvial system in western Washington. The 

Eocene of western Washington overlies a complex pre-Tertiary 

basement that is cut by thrust faults of mid-Cretaceous age 

and strike-slip faults of Late Cretaceous to early Eocene age 

(Whetten and others, 1988). The Chuckanut Formation unconformably overlies the pre-Tertiary rocks along the northern 

and southern contacts and is bounded by high-angle faults to 

the east (Misch, 1977; Tabor and others, 2003). The Chuckanut Formation was subdivided into seven members by Johnson 

(1984a), which are, in ascending order, the Bellingham Bay, 

Governors Point, Padden, Slide, Maple Falls, Warnick, and 

Bald Mountain Members. These units range in age from early 

to late Eocene. South of the main Chuckanut outcrop belt, the 
LEACH RIVER FAULT SAN JUAN FAULT 124° 122° 49° 48° 47° Gulf Islands Vancouver Glacier Vancouver Island Bellingham BasinMount Vernon Strait of Juan de Fuca

Puget

Sound

BK

C C

C C

C

C

R

S S

S

E F L F

N

N

M

MSB

C

CM

CB

C P F

R L F

MH

Ma

Victoria

Olympic 

Peninsula

Seattle

PortAngeles

MV

SEATTLE FAULT

Tacoma

P-TM

Chiwaukum graben

Methow graben STRAIGHT

CREEK

FAULT

PACIFICOCEAN

CANADA U. S. A.

Ch

CANADA

WASHINGTON

PUGET FAULT

Puget

Lowland

Coast

Range

Puget

Lowland

OzetteLake Crescent Lake

Strait of Georgia

WHIDBEY IS. FAULT ZONE

B

Northern

Cascades

HURRIC

A

N

E

R

D

I

GE

FAULT

A

A'

Figure 38. Generalized geologic map of northwestern Washington and southwestern British Columbia, Canada. Cross section A-A’ shown in fig

Bellingham; BK, Burrard and Kitsilano Formations; C, Chuckanut Formation ;CB, Chilliwack batholith; CM, Coal Mountain; CPF, Chewack-PasayteChumstick Formation; EF, Enitat fault; LF, Leavenworth fault; M, Manastash Formation; MH, Mount Higgins; MSB, Mount Stuart batholith; Ma, MaN, Naches Formation; P-TM, Puget Group and Tiger Mountain area (location of Raging River Formation); R, Roslyn Formation; RLF, Ross Lake faulFormation. Modified after Johnson (1984a), Snavely and Wells (1991), Snavely, MacLeod, and Niem (1993), and Mustard (1994).
Geologic Setting of Western Oregon and Washington Province 33

Figure 39. Outcrops of the lower to middle Eocene Crescent Formation. A, Exposure of 

basalt pillows and volcaniclastic rocks in road cut along Hurricane Ridge Road, Olympic 

National Park, Washington. B, Exposure of basalt pillows of the Crescent Formation in Salt 

Creek Park, Washington Route 112, Olympic Peninsula, Washington.

A

B
Bellingham Everett Mt. Vernon Bellingham Basin Victoria 123° 122° 49° 48° WHIDBEY ISLAND FAULT ZONE DEVILS MOUNTAIN FAULT Strait of Georgia San Juan Islands Strait of Juan de Fuca 

CM MH 00 25 50 KILOMETERS 25 50 MILES

Figure 40. Generalized geologic map of the Bellingham area, northwestern Washington, and Vancouver Island, Canada, showing rock units anfaults. CM, Coal Mountain; MH, Mount Higgins. Modified after Schuster (2005).
Geologic Setting of Western Oregon and Washington Province 35

rocks are assigned to the undivided Chuckanut at Coal Mountain, Mount Higgins, and in localities southeast of the town of 

Mount Vernon (figs. 38, 40).

Early Tertiary time in the Bellingham Basin was dominated by rapid uplift of pre-Tertiary rocks to the east, active 

strike-slip faulting, volcanic activity, and alluvial sedimentation in rapidly subsiding basins. The Bellingham Bay Member 

represents early Eocene deposition of the Chuckanut Formation and was interpreted by Johnson (1984a,b) as representing 

meandering-river and adjacent flood-plain deposits in a rapidly 

subsiding basin, with a distant source area to the east. Early 

reports by Woodruff (1914), Jenkins (1923, 1924), and Moen 

(1969) discussed the geology and coal deposits in this region. 

More recent investigations concerning the coal deposits have 

been published by Beikman and others (1961), Vonheeder 

(1975, 1977), and Brownfield and others (1995).

The Bellingham Bay Member of the Chuckanut Formation consists of nonmarine sandstone, mudstone, carbonaceous 

shale, and coal grouped into alternating coarse-grained and 

fine-grained sequences that represent fining-upward cycles 

(Johnson, 1984a); coals are near the base of the member. The 

Bellingham Bay Member is 8,860 ft thick in the western part 

of the outcrop belt and 10,830 ft thick in the eastern part of the 

outcrop belt, south of Glacier, Wash. (fig. 38).

Puget Lowland

The northern part of the Puget Lowland (or Seattle 

Basin), located southwest of the Northern Cascades (figs. 2 

and 38), is generally underlain by the basalts and volcaniclastic marine rocks of the lower to middle Eocene Crescent 

Formation (figs. 5, 7, and 39). In the late Paleogene, tectonism partitioned western Washington into smaller basins and 

uplifts (Wells and Coe, 1985), and sediments were deposited 

in fluvial, deltaic, and marginal marine environments over the 

basement volcanic rocks.

The lower(?) to middle Eocene Raging River Formation 

(fig. 5), named by Vine (1962), is the oldest sedimentary unit 

that outcrops in the eastern part of the central Puget Lowland 

in the Tiger Mountain area (figs. 38 and 41). Its base is not 

exposed in the area, but the exposed part ranges in thickness from about 2,000 ft to more than 3,000 ft (Vine, 1962; 

Vine, 1969; Johnson and O’Connor, 1994). The Raging River 

Formation consists of fine-grained sandstone, siltstone, and 

claystone. Johnson and O’Connor (1994) divided the Raging 

River into three informal units in the Tiger Mountain area. The 

lower unit is about 755 ft thick and consists of interbedded 

sandstone, mudstone, and conglomerate; the lower part of the 

lower unit is nonmarine, and the upper part is shallow marine 

in origin. The middle unit, about 610 ft thick, is mainly nonmarine interbedded conglomerate, sandstone, and mudstone. 

The upper unit consists of about 980 ft of gray, silty, organicrich mudstone and minor sandstone that was deposited along 

the marine shelf and bathyal slope and may also be present at 

depth to the west beneath Puget Sound.

The middle Eocene Tiger Mountain Formation of the 

Puget Group (fig. 5) overlies the Raging River Formation in 

the Tiger Mountain area (Vine, 1962; Vine, 1969; Johnson 

and O’Connor, 1994). The Tiger Mountain Formation is about 

2,000 ft thick and consists mainly of arkosic sandstone, siltstone, carbonaceous shale, and minor coal; the upper part of 

the unit interfingers with the middle to upper Eocene Tukwila 

Formation of the Puget Group (fig. 5). The Tukwila Formation 

consists mostly of volcanic and volcaniclastic rocks (Vine, 

1962; Vine, 1969; Johnson and O’Connor, 1994), ranges in 

thickness from 2,460 ft to as much as 6,800 ft in the Tiger 

Mountain area (figs. 38 and 41), and possibly interfingers 

with the overlying middle to upper Eocene Renton Formation 

also of the Puget Group. The Renton Formation, 2,250 ft to 

more that 3,400 ft thick (Vine, 1962; Vine, 1969; Johnson and 

O’Connor, 1994), consists mainly of fine- to medium-grained 

arkosic sandstone with lesser amounts of siltstone; it also consists of carbonaceous shale as well as minor coal.

Upper middle Eocene and upper Eocene coal-bearing 

strata in the central and northern parts of the Puget Lowland 

(Beikman and others, 1961) are assigned to the undivided 

Puget Group (fig. 5) (Vine, 1969). Vine (1969) compiled a 

composite 5,250-ft-thick stratigraphic section based on surface 

and shallow subsurface data in the Green River district southeast of Seattle (fig. 2). The Green River district is structurally 

complex with numerous faults and tight folds with beddingplane attitudes ranging from gentle to overturned. At the John 

Henry No. 1 mine, coal was mined along the flanks of a tightly 

folded anticline that illustrates this structural style (fig. 42) 

(Brownfield and others, 1994; Brownfield and others, 2005).

Sedimentological analysis of the undivided Puget Group 

in the Green River district is limited due to the distribution 

and poor quality of the exposures. The following preliminary interpretation is based mainly on the 6,300-ft measured 

section by Vine (1969) exposed in the canyon of the Green 

River and at the John Henry No. 1 mine near Black Diamond, 

Wash. (fig. 42) (Brownfield and others, 1994; Brownfield and 

others, 2005). Rocks in the Green River section of the Puget 

Group dip gently to steeply exposing most of the coal-bearing 

stratigraphic interval; however, there is virtually no control 

on the lateral distribution of facies, because of the extensive 

forest cover. The Puget Group section consists of alternating 

sequences of coarse-grained sandstone and fine-grained deposits of mudstone, very fine to fine-grained sandstone, and coal 

having characteristics of both deltaic and fluvial environments 

(Brownfield and others, 1994). The delta was fluvial-dominated, but influenced by tides and to a lesser extent by waves. 

The fluvial deposits include both channel and interchannel 

strata.

Puget Group strata of fluvial origin within the Green 

River canyon and in the vicinity of, and within, the John 

Henry mine form sandstone bodies ranging in thickness from 

about 20 to 158 ft (Brownfield and others, 1994; Brownfield 

and others, 2005). These bodies consist mainly of fine- and 

medium-grained sandstone; coarse-grained sandstone is 

uncommon, and conglomerate is rare. Channels typically 
36 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province Puget Sound

0

0 25 50 KILOMETERS

25 50 MILES

Olympia

Centralia

Northcraft

Formation

(volcanic center)

Puget Lowland

WIF

Puget Lowland

Puget Lowland

Wilkeson

Morton

Seattle

Black

Diamond

TM

COAST RANGE BOUNDARY FAULT

OR PUGET FAULT

123° 122°

48° 

47° 

Pre-Tertiary rocks,

 undivided

Paleogene rocks,

 undivided

Crescent Formation and

 Metchosin Volcanics

Northcraft Formation

Quaternary deposits

Fault, dashed where infurred

City

Tertiary intrusive

 rocks

Pre-Tertiary intrusive

 rocks

Columbia River Basalt

 Group

Quaternary to Tertiary

 volcanic rocks, undivided

Water

EXPLANATION

Strait of Juan

de Fuca

Figure 41. Generalized geologic map of the Puget Lowland area, northwestern Washington, showing geologic units and 

major faults. TM, Tiger Mountain; WIF, Whidbey Island fault. Modified after Schuster (2005).
Geologic Setting of Western Oregon and Washington Province 37

Figure 42. Outcrops of the Puget Group at the Pacific Coast Coal Company’s John Henry 

No. 1 mine near Black Diamond, Washington (see fig. 41). The strata dip steeply over a 

doubly plunging anticline on the left side of the photograph.

Figure 43. Outcrop of the Franklin No. 10A coal bed in John Henry No. 1 mine near Black 

Diamond, Washington (see fig. 41). Rocks above coal consist of fine-grained overbank 

deposits, cut into by a thick channel sandstone, which is overlain by a fine-grained 

floodbasin facies.
38 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

have sharp, erosional lower contacts (fig. 43), and many 

sandstone bodies include internal low-angle, trough-shaped 

scour surfaces that can be traced laterally for as much as 50 ft. 

Both basal and internal scour surfaces are commonly overlain 

by lags of wood fragments (with rare Teredo borings) and 

rip-up clasts. The sandstone is trough crossbedded, planar to 

low-angle bedded, and ripple laminated. Thick (13–33 ft) sets 

of low-angle (10°–20°) dipping strata, interpreted as lateral 

accretion surfaces on point bars, are present in several sandstone bodies. Fine-grained mudstone drapes, in many cases 

burrowed, are present on bedding planes within point-bar 

deposits. A fluvial channel origin for these sandstone bodies is 

inferred based on texture and internal sedimentary structures, 

as outlined above. Location of these channels on a delta plain 

is supported by the presence of burrowed mudstone drapes 

on point-bar deposits (Thomas and others, 1987; Shanley and 

others, 1992), Teredo-bored wood, and the sedimentology of 

bounding fine-grained strata.

Puget Group strata that are interpreted as interchannel 

deposits (including levee, flood-plain, shallow-lake, crevassechannel, crevasse-splay, and peat-swamp environments) consist of mudstone and fine-grained sandstone, and less common 

carbonaceous shale and coal (Brownfield and others, 1994; 

Brownfield and others, 2005). These fine-grained units are 3 

to more than 65 ft thick. Parallel and (or) ripple lamination is 

common; however, in many cases primary sedimentary structures have been partly or wholly destroyed by burrows, root 

traces, and pedogenesis. Fossil plant material is common in 

these beds (Wolfe, 1968; Burnham, 1990). Within the thicker 

fine-grained intervals, two types of deposits are recognized: 

(1) lenticular beds of ripple-laminated, horizontal-bedded, and 

trough-crossbedded, very fine to fine-grained sandstone generally less than 3 ft thick interpreted as crevasse-channel deposits; and (2) sheet-like beds of ripple-laminated and horizontalbedded, very fine to fine-grained sandstone generally less than 

1.5 ft thick inferred to be crevasse-splay deposits.

Beds of coal, carbonaceous shale, and minor mudstone 

representing peat-swamp deposition are also present in the 

Puget Group, ranging in thickness from a few inches to as 

much as 40 ft. Altered tuff beds or tonstein partings are common in the stratigraphically lower coal, indicating moderate 

Paleogene volcanism during the time of peat accumulation. 

Tonsteins are rare to absent in stratigraphically higher coal 

beds. The clastic section above the Franklin No. 10A coal bed 

in the John Henry No. 1 mine consists of fine-grained overbank deposits that are cut into by a large channel sandstone, 

which is overlain in turn by more fine-grained floodbasin 

facies (fig. 43). Vertical tree trunks and petrified wood are 

present in several coal beds. Burnham (1990) suggested that 

coals of the Puget Group formed in raised mires; however, the 

abundance of mudstone partings and tonsteins in many coals 

suggests that peat swamps also occupied low-lying parts of the 

delta plain.

Strata of inferred brackish to shallow-marine origin 

consist of stratified to massive sandstone and mudstone. 

Stratification includes parallel and ripple lamination, wavy, 

flaser, and lenticular bedding, and relatively small-scale 

trough crossbedding (set thickness <1 ft). Crossbed sets are 

bidirectional (dipping up and down the regional paleoslope) 

and contain common mudstone drapes. Mudstone drapes 

and thin (<0.2 in.) carbonaceous laminations are common. 

This suite of sedimentary structures indicates fluctuating 

depositional energy and probable tidal influence (Shanley 

and others, 1992). Hummocky crossbedding and wave-ripple 

lamination are rare but indicate minor wave influence. Primary stratification has been partly to completely destroyed in 

many sandstone and mudstone beds of inferred brackish to 

shallow-marine origin by intensive bioturbation. Burrowing 

animals led to differential cementation in many beds, resulting commonly in an irregular and knotty weathering profile. 

Plant fragments, including Teredo-bored wood, are common 

in massive sandstone beds; shell fragments (pelecypod and 

gastropod) are present in a few beds. Evidence for both tidal, 

and to a lesser degree, wave influence, indicates deposition in 

a variety of delta-plain and delta-front environments, including 

bays, estuaries, mouth bars, and shorefaces.

Coal-bearing rocks in the Wilkeson-Carbonado area 

(figs. 2 and 41) are in the middle Eocene Carbonado Formation of the Puget Group (fig. 5) and consist of interbedded 

sandstone, siltstone, mudstone, carbonaceous shale, and coal 

more than 5,000 ft thick (Gard, 1968). The basal contact of 

the Carbonado Formation is not exposed and in places is 

overlain by the Northcraft Formation of Puget Group. Where 

the Northcraft Formation is absent, the Carbonado is indistinguishable from Spiketon Formation of Puget Group (fig. 5).

North of Morton, Wash. (fig. 41), the Carbonado Formation (fig. 5) is about 3,900 ft thick (Johnson and Stanley, 

1995) and consists of nonmarine and shallow- to marginalmarine rocks deposited in fluvial and tidally influenced delta 

environments. The marine rocks are shoreface sandstone 

and laminated sandstone and mudstone, and the nonmarine 

rocks include sandstone, mudstone, coal, and carbonaceous 

mudstone.

Southern Puget Lowland

The oldest rocks exposed in the southern Puget Lowland 

area (figs. 5 and 44) are the lower Eocene Crescent Formation, which is unconformably overlain by the middle to upper 

Eocene McIntosh Formation (fig. 5). The McIntosh Formation consists of dark-gray marine siltstone and mudstone and 

interbedded arkosic and basaltic sandstone ranging in thickness from 4,000 to 4,500 ft (Snavely and others, 1951, 1958). 

Overlying the McIntosh is the coal- and carbonaceous-shalebearing Skookumchuck and Cowlitz Formations (fig. 5).

The upper middle to upper Eocene Skookumchuck 

Formation (fig. 5) crops out in the Centralia-Chehalis district 

(fig. 2), where the stratigraphy and coal geology was described 

in detail by Snavely and others (1958). The Skookumchuck 

is about 3,825 ft thick in the district and consists of marginalmarine and shallow-marine rocks. Although present only in 

the Centralia-Chehalis district, the formation can be correlated 
Geologic Setting of Western Oregon and Washington Province 39

123°

47°

46°

Longview

Willapa

Portland

Puget Lowland

Puget Lowland

Centralia

Olympia

WASHINGTON

OREGON

Columbia River

Hills

0 10 20 MILES

0 10 20 KILOMETERS

Crescent Formation

Northcraft Formation

Neogene rocks, undivided; includes, in

 part, Astoria and Montesano Formations

Quaternary deposits

City

Tertiary intrusive

 rocks

Columbia River Basalt

 Group

Quaternary to Tertiary

 volcanic rocks, undivided

Water

EXPLANATION

Paleogene rocks, undivided; includes,

 in part, McIntosh, Cowlitz, Lincoln

 Creek, and Skookumchuck Formations 

Northcraft

Formation

(volcanic center)

Figure 44. Generalized geologic map showing the southern part of the Puget Lowland and the Centralia coal area, 

southwestern Washington. Modified after Schuster (2005).
40 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

to other coal-bearing time-stratigraphic units to the north and 

south (fig. 3). The Skookumchuck Formation overlies and 

interfingers with the Northcraft Formation and is overlain by 

the Oligocene Lincoln Creek Formation (fig. 5). 

Sedimentological evidence of detrital rocks in the 

Skookumchuck Formation in the Centralia mine (figs. 44 and 

45) indicates that these deposits formed in a tidal-influenced 

coastal plain (Stevenson and Emery, 1958; Evans, 1965; 

Reineck and Singh, 1980). Within this setting, fine-grained 

rocks were deposited in tidal flats and coarser grained rocks 

(for example, sandstones) were deposited in tidal channels and 

bars. Lenticular, wavy, and flaser bedding; bidirectional ripple 

lamination; and mudstone drapes indicate fluctuating depositional energy and reversals of current direction. Abundant 

or topogenous. Clastic material would be unable to flow into 

raised mires, and volcanic ash would have been washed and 

dispersed into the peat by rainfall (Rupert and others, 1993; 

Rupert and Moore, 1993).

The middle to upper Eocene Cowlitz Formation, which 

crops out southwest of Centralia and northwest of Longview 

in the Willapa Hills (fig. 44), was deposited in marine, brackish-water, and nonmarine environments. At the type locality 

along the Cowlitz River, north of Longview, Wash. (fig. 44), 

the Cowlitz Formation is about 4,200 ft thick and is predominantly siltstone with massive arkosic sandstone, locally 

well developed, and sandy siltstone with minor amounts of 

coal and carbonaceous shale (Weaver, 1937; Roberts, 1958). 

The sandstone beds are mostly arkosic and are as much as 

90 ft thick. Regionally, the Cowlitz Formation is as much as 

9,500 ft thick and equivalent to the Skookumchuck Formation 

and in part to the McIntosh Formation (fig. 5) (Armentrout and 

others, 1980).

The Oligocene Lincoln Creek Formation (fig. 5) crops 

out west and east of Centralia, Wash. (fig. 44) (Snavely and 

others, 1958); it underlies much of the area east of Grays 

Harbor and Willapa Bay (fig. 7) and conformably overlies the 

Skookumchuck Formation. The Lincoln Creek Formation, 

where it crops out east of Centralia, consists of nearshore and 

continental units. These units grade laterally into marine tuffaceous siltstone and fine-grained sandstone that are about 1,500 

ft thick near Centralia (fig. 44). The Lincoln Creek Formation thickens westward to as much as 9,000 ft thick southeast 

of Grays Harbor (fig. 7, also see fig. 54), where the Lincoln 

Creek Formation is predominantly marine tuffaceous siltstone 

and fine-grained tuffaceous sandstone (Armentrout and others, 

1980).

The lower to middle Miocene Astoria Formation unconformably overlies the Lincoln Creek Formation in the southern 

Puget Lowland, where late Oligocene structural highs had 

developed. Because of these unconformable relations, the 

thickness of the Astoria Formation is variable, measuring only 

about 700 ft in the southern Puget Lowland area but increases 

to nearly 3,500 ft just east of Grays Harbor (fig. 8; also see 

fig. 54) (Rau, 1967). In the Centralia, Wash., area (fig. 44), the 

Astoria Formation consists generally of dark, medium-grained 

and carbonaceous fine-grained sandstone and locally glauconitic sandstone beds at its base (Armentrout and others, 1980). 

East of Centralia, the Astoria Formation contains basaltic 

conglomerate (Snavely and others, 1958).

Olympic Peninsula Area

The Tofino-Juan de Fuca Basin is located on the northern 

Olympic Peninsula of Washington (fig. 46) and occupies the 

Strait of Juan de Fuca (fig. 46). The Canadian term for this 

basin is the Tofino Basin (Shouldice, 1971), and Snavely and 

others (1980) referred to the basin as the Tofino-Fuca Basin. 

The Tofino-Juan de Fuca Basin is bounded on the north by 

Vancouver Island and to the south by the Olympic Mountains. 

Subsidence began in the middle Eocene resulting from thermal 

Figure 45. Outcrop showing the Big Dirty coal bed of the 

Skookumchuck Formation, in the Hanaford pit, at the Centralia 

mine, west of Centralia, Washington (see fig. 44). The coal bed is 

as much as 40 ft thick. White band is a volcanic ash parting.

fossils, fossil fragments, and trace fossils indicate widespread 

biologic activity. Zones of root structures in these inferred 

intertidal deposits indicate periodic exposure in supratidal 

environments.

Tidal-channel deposits are observed in a variety of scales. 

Larger channels are represented by units of scour-based, 

trough-crossbedded sandstone and include Teredo-bored wood 

fragments. A large channel deposit traverses the Big Dirty 

coal bed in the North Hanaford pit of the Centralia mine, 

east of Centralia, Wash. (fig. 44), indicating channel incision 

into a supratidal mire (Brownfield and others, 1994). Deposits of smaller tidal channels include relatively thin sets of 

tabular-crossbedded, silty to fine-grained sandstone units with 

reactivation surfaces that are interpreted as tidal bar deposits 

(Boersma and Terwindt, 1981).

The coal beds represent peat accumulation in supratidal 

mires that formed above mean high-tide level. The presence of 

abundant mudstone and of both airfall and water-laid volcanicash partings (fig. 45) suggests that these mires were low lying 
Geologic Setting of Western Oregon and Washington Province 41

cooling of the Crescent Formation basement rocks (Johnson 

and others, 1997). In the southern part of the basin, there are 

more than 28,000 ft of northward-dipping rocks of middle 

Eocene to early Miocene age (figs. 47 and 48) (Brown and 

others, 1960; Gower, 1960; Snavely and others, 1980; Snavely, 1983; Snavely and others, 1993b; Schasse, 2003), including lithic arkosic to lithic turbidite sandstone and deep-marine 

mudstone and minor amounts of conglomerate and sedimentary breccia. The middle to upper Eocene Aldwell Formation 

(fig. 47), which unconformably overlies the oceanic basalt of 

lower Eocene Crescent Formation oceanic basalt, is predominantly marine mudstone and siltstone with minor amounts of 

sandstone, conglomerate, and lenses of pillow basalt, volcanic 

breccia, and tuff; average thickness is 2,000 ft (Brown and 

others, 1960). The Aldwell Formation is overlain unconformably by the upper Eocene Lyre Formation, at least 2,200 ft 

thick, consisting of massive, medium- to coarse-grained conglomerate and interstratified gray to grayish-brown, coarsegrained, massive sandstone with pebbly conglomerate beds 

and minor thin-bedded siltstone and shale. Snavely and others 

(1978) divided the overlying Twin River Group (fig. 47) into 

the Hoko River, Makah, and Pysht Formations, with combined 

thicknesses as much as 17,500 ft. The Hoko River Formation 

conformably overlies, or intertongues with, the Lyre Formation and ranges in thickness from 5,250 to 7,550 ft; it contains 

fossiliferous siltstone with interbedded phyllitic and basaltic 

sandstone, pebbly sandstone, and conglomerate (Snavely and 

others, 1978, 1980; Prothero and others, 2009). The Hoko 

River Formation is gradationally or locally unconformably 

overlain by 7,550 to 9,200 ft of the Makah Formation, which 

consists of turbidite sandstone and siltstone. The Makah Formation is gradationally or unconformably overlain by 3,610 to 

4,590 ft of the Pysht Formation and contains gray to olivegray massive mudstone, sandy siltstone with minor interbeds 

of sandstone, and conglomerate channels. The Pysht Formation is overlain by the lower Miocene Clallam Formation, 

which forms the upper part of the sedimentary sequence that 

filled the deep-marine Juan de Fuca Basin (fig. 47) (Niem and 

48° 

124° 

CANADA

UNITED STATES

Tofino-Juan de Fuca Basin

Pacific Ocean

Vancouver

Island

Olympic Peninsula

Port

Angeles

Victoria

Cape

Flattery

DISCOVERY

BAY FAULT

Metchosin

Volcanics Strait of Juan de Fuca

Pre-Tertiary rocks

Syncline

Anticline

Tertiary Ozette terrane Fault

 and melange or broken

 formation

Sedimentary rocks interbedded

 with the Crescent Formation

Eocene Crescent Formation

 and the Metchosin Volcanics

 on Vancouver Island

Quaternary deposits and

 Tertiary sedimentary rocks

EXPLANATION

0 15 MILES

0 15 KILOMETERS

Thrust fault, teeth on

 upper plate

A

A'

Figure 46. Generalized geologic map of the northern part of the Olympic Peninsula, Vancouver Island, Canada, 

and the Tofino-Juan de Fuca Basin. Cross section A–A’ shown in figure 48. Modified after Tabor and Cady 

(1978a), Niem and Snavely (1991), and Johnson and others (1997).
42 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Clallam Formation

Pysht Formation

Makah Formation

Hoko River

Formation

Aldwell Formation

Crescent Formation

Ozette and adjacent

terranes

Lower

 Miocene Oligocene Upper Eocene Middle Eocene Lower Eocene Middle and upper Eocene (with some pre-Tertiary blocks)

Siltstone of Brownes Creek

Lyre

Formation

Twin River Group

Jansen Creek

Member

Third Beach

Member

Klachopis Point

Member

Dtokoah Point Mbr.

Baada Point

Mbr.

Figure 47. Stratigraphic column 

showing rocks of the Tofino-Juan de 

Fuca Basin, northwest Washington, and 

Vancouver Island, Canada. Modified 

after Snavely and others (1978), Niem 

and Snavely (1991), and Snavely and 

others (1993). Not to scale.

Snavely, 1991). The Clallam Formation ranges in thickness 

from 1,970 to 2,625 ft (Addicott, 1976) and contains predominantly marine sandstone, sandy siltstone, and conglomerate, 

with thin coal beds and carbonaceous mudstone and siltstone 

in the upper part of the formation. The Crescent Formation and 

the middle to upper Eocene Ozette terrane (figs. 47 and 48) 

along the southern part of the basin, have been underthrusted 

by the melange and broken formation terranes of the Olympic 

Peninsula (Tabor and Cady, 1978a; Schasse, 2003).

Sedimentary rocks in the Tofino-Juan de Fuca Basin represent several depositional environments (Niem and Snavely, 

1991). The bathyal slope, outer fan, and basin-plain environments are indicated by thick mudstone units with minor distal 

turbidites represented by the middle and upper Eocene Aldwell 

and the Oligocene and lower Miocene Pysht Formations 

(Snavely and others, 1978; Snavely, 1983). The submarine-fan 

and gravel-slope wedges include the Lyre Formation (fig. 47) 

and informal upper Eocene Cape Flattery breccia (Brown and 

others, 1956; Ansfield, 1972). Slope and basin turbidite flows 

and middle to outer fan conglomerate channels are identified 

in the upper Eocene Hoko River Formation (Ansfield, 1972; 

De Chant, 1989), with turbidite fans in an outer- to mid-fan 

environment identified in the upper Eocene to lower Miocene 

strata of the Makah and Pysht Formations (Brown and Gower, 

1958; Rau, 1964; Snavely and others, 1980). The marine 

units in the basin were mostly derived from (1) Paleozoic 

and Mesozoic low-grade metamorphic, granitic, and volcanic rocks, and eroded sedimentary-sourced terranes on the 

southern part of Vancouver Island (Snavely and others, 1980; 

Niem and Snavely, 1991); and (2) local lower Eocene Crescent 

Formation and Metchosin Volcanics (figs. 4 and 46) (Brown 

and others, 1960; Snavely, 1983). The Clallam Formation was 

deposited mostly as a marine unit with the upper part deposited in a coal-bearing deltaic environment.

The central and western part of the Olympic Peninsula 

is characterized as accretionary terrane (fig. 3) that formed 

during convergence between the Pacific and North American 

plates during late Eocene and middle Miocene time, producing two melange terranes. The absence of blueschist-facies 

rocks and ultramafic rocks is further evidence that the Olympic core rocks were accreted and subducted and mixed with 

mantle material (Tabor and Cady, 1978b). The only onshore 

exposures of the terranes are within the western part of the 

Olympic Peninsula, where they were transported eastward to 

form the core of the Olympic Mountains west of the Hurricane 

Ridge fault (figs. 38, 49, and 50). Surrounding this core area 

is a rim-shaped area of peripheral rocks consisting of lower 

to middle Eocene oceanic basalt and volcaniclastic rocks of 

the Crescent Formation (figs. 7 and 51) overlain by sedimentary rocks of Eocene to Miocene age. The two terranes in the 

western part of the Olympic core are known as the Ozette terrane that formed during the late Eocene convergence and the 

Hoh rock assemblage that formed during the late Oligocene 

to middle Miocene convergence (fig. 51) (Rau 1975, 1979; 

Tabor and Cady, 1978b; Snavely and Kvenvolden, 1989). The 

two terranes, both of which contain organic-rich rocks, have 
A

Sea level 

1,0002,0003,0004,0005,0006,0007,0008,0009,000

Olympic Peninsula Strait of Juan de Fuca 

CALAWAH FAULT

(CONCEALED)

Crescent thrust

Coastline

Sekiu River

Depth in meters

T A

Magnetic

high

EXPLANATION

Makah FormationHoko River Formation

Lyre Formation

Aldwell Formation

Crescent Formation

Quaternary glacial driftLower Pliocene and upper Miocene(?) strataClallam FormationPysht Formation Ozette terrane and other core rocks of middle and late Eocene age (melange and broken formation)

Pre-Tertiary basement rocks

0 5 KILOMETERS0 

Figure 48. Generalized structure cross section of the Tofina-Juan de Fuca Basin across Strait of Juan de Fuca extending from the northern paPeninsula to the southern part of Vancouver Island, Canada. Location of cross section shown in figure 46. Modified after Snavely (1983) and Nie(1991).
44 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

EXPLANATION

Olympic accretionary

 wedge

Quaternary to Eocene

 peripheral rocks

Basaltic rocks of 

 Crescent Formation

?

Thrust fault—Queried

 where uncertain,

 sawteeth on upper plate

High-angle fault—Dashed

 where inferred

City or town

WASHINGTON

Area of map

Index map

124° 123°

48°

Cape 

Flattery

Port

Angeles

Sequim

Sappho

Forks

Tahola

Quilcene

Staircase

Mt

Olympus

Mt

Anderson Mt

Constance

Steeple

Rock

Mt

Angeles

S tr a i t o f J u a n d e Fu c a

Ozette Lake

Lake Quinault Lake 

Cushman Hood

Mt Stone Canal

Capitol

Peak

Pacific Ocean

FAULT

CALWAH

HURRICANE 

?

?

RIDGE FAULT

SOUTHERN

FAULT ZONE

0

0 10 20 KILOMETERS

10 20 MILES

Figure 49. Generalized geologic map showing major rock units and faults on the Olympic Peninsula. Modified after 

Tabor and Cady (1978b).
Geologic Setting of Western Oregon and Washington Province 45

5

T

30

Sea level

5

10

Depth in kilometers

15

20

25

Salmon River

thrust

SOUTHERN

WHIDBEY ISLAND

FAULT ZONE 

A'

Olympic subduction complex Olympic peripheral rocks

OS

OS OS

OS

OS

OS

OS

OP

OP

Bend 

in section

Crescent Formation

pre-Tertiary

continent

CN

Juan de Fuca plate 

Mount Olympus

(12–14 km = depth of accretion

of now-exposed rocks

HURRICANE

RIDGE

FAULT

Sedimentary

rocks

Sedimentary

rocks

A

Crescent Formation and 

 peripheral rocks (OP)

? ?

?

A

Migmatite

Fault

Displacement on

 strike-slip fault

 T, toward

 A, away

Trace of bedding

Contact, unfaulted

Pre-Teriary rocks

Paleogene sedimentary rocks,

 includes Chuckanut Formation

 and Puget Group (CN)

Pliocene to lower Eocene Olympic

 subduction complex forming an

 accretionary wedge (OS)

Oceanic lithosphere of the Juan de

 Fuca plate

EXPLANATION

Figure 50. Structure cross section showing the lower Eocene to Pliocene Olympic subduction complex that formed an 

accretionary wedge on the Olympic Peninsula, the Olympic peripheral rocks, and the Paleogene sedimentary rocks of 

northwest Washington. Location of section is in figure 38. Modified from Tabor and Cady (1978b), Johnson and others 

(1996), Brandon and others (1988), and Brown and Dragovich (2003).

been differentiated on the basis of biostratigraphic data. The 

Ozette melange (fig. 51), of unknown thickness, includes lithic 

sandstone and siltstone turbidite beds and minor conglomerate, 

coal, and carbonaceous sandstone and siltstone. The Hoh rock 

assemblage (fig. 51) includes at least 8,200 ft of lithic feldspathic sandstone and siltstone turbidite beds (figs. 52 and 53) 

and minor amounts of conglomerate, coal, and carbonaceous 

sandstone and siltstone (Snavely and Kvenvolden, 1989).

Southwestern Washington Area

The oldest rocks exposed in southwestern Washington 

are Paleogene in age and include the Crescent Formation, the 

lower part of the Hoh rock assemblage, and the McIntosh, 

Cowlitz, and Lincoln Creek Formations (figs. 5 and 54) all 

of which are described in previous sections for other areas in 

which they are present. The post-Crescent Formation Tertiary 

rocks are about 15,000 ft thick in the Grays Harbor and Willapa Bay areas and to the east (Rau, 1967, 1968).

The upper Eocene to Oligocene Lincoln Creek Formation 

(fig. 8) consists mostly of marine tuffaceous mudstone, siltstones, and fine-grained sandstones ranging in thickness from 

2,000 to more than 9,000 ft in southwest Washington (Rau, 

1966, 1967; Beikman and others, 1967). The siltstone and 

silty sandstone beds are thick, displaying little bedding except 

where tuff or concretionary layers are present. Some altered 

tuff beds have been identified in the Lincoln Creek Formation 

ranging in thickness from a few inches to a few feet (Rau, 

1967).

Shallow marine and deltaic rocks, of the lower to middle 

Miocene Astoria Formation and the middle to upper Miocene 

Montesano Formation, crop out in southwest Washington 

(fig. 54). The Astoria Formation unconformably overlies the 

Lincoln Creek Formation in areas to the east where structural 

highs are present, but the two are conformable elsewhere. 

The Astoria Formation is estimated to be about 3,500 ft thick 

northeast of Grays Harbor and consists of marine organicrich mudstones, siltstones, and fine- to coarse-grained lithicfeldspathic and arkosic sandstones with minor conglomerates 

(fig. 44) (Rau, 1967; Walsh and others, 1987). The rocks of the 

Astoria Formation are commonly massive but include locally 

sourced conglomerate and concretionary beds. The Astoria 

Formation can be differentiated from the underlying Lincoln 

Creek Formation by the increase in carbonaceous material, 

the lack of tuffaceous material, and generally having better 

bedding.
Cape Flatery 124° 123° 48° S tr a it o f J u a n d e Fu c a Pacific Ocean W e s t e r n E a s t e r n c o r e c o r e Peripheral rocks Peripheral rocks Hood Canal ? ? ? WASHING

Area of m

Index ma

Middle  with s coast, Fault, q

Area of 

Oligoce the OzEocene 

Core rocks Upper M

Middle  of the Contac

Peripheral roc

?? Thrust 

 sawte

00 10 20 KILOMETERS

10 20 MILES

Figure 51. Map showing the different core terranes and peripheral rocks on the Olympic Peninsula. Modified after Tabor and Cady (1978b).
Geologic Setting of Western Oregon and Washington Province 47

Figure 52. Outcrop of 

the upper Oligocene 

to middle Miocene 

Hoh rock assemblage 

turbidites along Beach 

4, Washington coastline. 

The top surfaces of the 

beds face to the left, 

indicating that the beds 

are overturned.

Figure 53. Close-up 

view of the upper 

Oligocene to middle 

Miocene Hoh rock 

assemblage turbidites 

along Beach 4, 

Washington coastline. 

Parallel laminated 

sandstones below 

and right of knife. 

Top surfaces of the 

beds face to the left, 

indicating that the beds 

are overturned.
Hoquiam COLUMBIA RIVER ? ?? ? ? BIG CREEK THRUST FAULT 124° 47°

46°

00 10 20 KILOMETERS

10 20 MILES

OREGON

WASHINGTON

PACIFICOCEAN

GRAYSHARBOR

WILLAPA BAY

Astoria

Aberdeen

Hoh rockassemblage(Rau, 1986)

HumptulipsFormation(Rau, 1986)

Paleogene roc in part, lower  assemblage,  Humptulips, a Formations Crescent Form and volcanicl

Neogene rocks in part, upper  assemblage,  Formations

Quaternary depThrust fault, da sawteeth on uCityTertiary intrusi rocksColumbia Rive GroupQuaternary to T volcanic rock

Water

EXPLANAT

Ocean City

Strike-slip fau inferred

WISHKAHTHRUST FAULTS

Figure 54. Geologic map of southwestern Washington showing selected geologic units. Modified after Rau (1986), Walsh and others (1(1987), and Palmer and Lanley (1989).
Geologic Setting of Western Oregon and Washington Province 49

The Miocene Montesano Formation unconformably overlies the Astoria Formation, is as much as 2,500 ft thick (Rau, 

1967), and occurs over a large area surrounding Aberdeen, 

Wash. (fig. 54). The lower part of the Montesano Formation 

consists of about 1,500 ft of fine-grained sandstone (fig. 55) 

with minor amounts of conglomerate and mudstone; the upper 

part consists of about 1,000 ft of tuffaceous mudstone and 

sandy siltstone (Fowler, 1965, 1966). East of Grays Harbor, 

the Montesano Formation averages 1,800 ft thick and is composed mostly of fine- to medium-grained sandstone, pebbly 

sandstone, and conglomerate, indicating a probable sediment 

source area to the east.

Several periods of deformation occurred in southwestern 

Washington since the middle Eocene, resulting from convergence of the Pacific and North American plates. These 

included the tectonic processes of crustal shortening, thrust 

and strike-slip faulting, and block rotation (Wells and Coe, 

1985; Rau, 1986). The first period of deformation resulted 

in the late middle to early late Eocene underthrusting of the 

organic-rich Hoh rock assemblage, and possibly also the 

Ozette melange, beneath the Crescent Formation along the Big 

Creek thrust fault (fig. 54) (Rau, 1986; Snavely and Kvenvolden, 1989; Snavely and others, 1993b). Contemporary with 

this thrusting event, east–west strike-slip faulting offset both 

rock assemblages and the Crescent Formation. The Big Creek 

thrust fault (fig. 54) was interpreted as a middle Tertiary plate 

boundary by Johnson and others (1997, their fig. 10); they 

placed the boundary along the eastern edge of Grays Harbor. 

Snavely and Wagner (1982) and Snavely (1987), however, 

placed this plate boundary just offshore (westernmost thrust 

fault in fig. 54); west of the plate boundary (fig. 56, fault A), 

the Miocene shallow-marine rocks of the Montesano Formation were deposited on the lower plate, which consists of the 

Hoh rock assemblage (Rau, 1973) and possibly the rocks 

of the Ozette terrane (Snavely and Wagner, 1982); Snavely, 

1987; Snavely and others, 1993b). To the east of the plate 

boundary of Snavely and Wagner (1982, 1987), the Astoria 

and Montesano Formations were deposited over the Crescent 

Formation on the upper plate (fig. 56). The southern extension 

of the Big Creek thrust fault may be fault B of Snavely and 

Wagner (1982) and Snavely (1987) (fig. 56), and the Hoh rock 

assemblage could be present below the Crescent Formation at 

depth, but the lack of onshore seismic reflection profiles limit 

the deeper projection of geologic formations (fig. 56).

The second major period of deformation occurred in the 

middle Miocene and resulted in faulting along the Wishkah 

thrust faults and folding within the Humptulips and Astoria 

Formations, but did not affect the upper Miocene Montesano 

Formation (figs. 54 and 55) (Rau, 1986). Strike-slip faults 

offset the Crescent and Humptulips Formations during the 

same deformation period. The third period of deformation followed the deposition of the Miocene Montesano and resulted 

in gentle folding and minor faulting. Figure 56 shows the 

Figure 55. Exposure of arkosic sandstone and siltstone in the middle to upper Miocene 

Montesano Formation in road cut along U. S. Highway 12, east of Aberdeen, Washington 

(see fig. 54).
2.1 3.2 4.7 km/sec. 5.8 km/sec., top of oceanic crust (?) A A' 

Sea level 2,000 4,000 6,000

Depth,

 in meters

Fault A Fault B

Diapir

Tmo

To

Tp

Tmm

Tmu

Tmo

Tmo Tml

Tmu Tmm

Tml Tmo

Tml

Tmm

To? To? To To

To

To

? ?

?

? ? ? ? ? 

To

To

To

Qu Qu

Tml Tmm

Qu

Tmo? Tmo?

Tmu

Qu Tp

Coastline(1) Conoco RA 1747 T.D. 443 m Shell Oil Co. P-0155 T.D. 3,402 m

Qu

Tcr

Tm

Ta

Tcr

Qu

Toe

Toe

Tcr

Ta

Ta

Toe 

(2)

Conoco

Hogan Estate No. 1

T.D. 1,203 m

S

Weyerha

Diapir

? ? ?

Station G-7

(projected)

00 10 

1

A A'

GRAYLANDA

(1)

WILLAPA

BAY

Station

G-7

Shell Oil Co

P-0155

Shell Oil Co

P-0150

200

100

400

600

600

800

125°00’ 124°30’ 124°00’ 

47°00’46°30’

PACIFICOCEAN

GRAYSHARBOR

Exploration well

Hoh rock assemblage (Rau 1975, 1979) Offshore time-stratigrahic units Onshore units 

Index Map 

Holocene and Pleistocene depositsPliocene strataUpper middle Miocene to upper Oligocene strataOligocene strataUpper Miocene strata, includes Montesano FormationMiddle Miocene strataLower Miocene strata

Quaternary depositsMontesano Formation

Astoria Formation

Middle Oligocene to Eocene strata, undifferentiated

Fault—Showing relative movement, dashed where inferredCrescent Formation

EXPLANATION

Figure 56. Structure cross section across part of the inner continental shelf and adjacent Coast Range of southwestern Washington. Offshore gbetween A and A’ based on interpretation of 24-channel seismic data and subsurface data from Shell Oil Company exploration well P-0115 (see inOnshore Quaternary and Tertiary unit symbols include: Qu, Quaternary deposits; Tm, Montesano Formation; Ta, Astoria Formation; Toe, undivided Oligocene to Eocene units; Tcr, Crescent Formation. Offshore time-stratigraphic units include: Qu, Holocene and Pleistocene deposits; Tp, Pliocenupper Miocene strata; Tmm, middle Miocene strata; Tml, lower Miocene strata; Tmo, upper middle Miocene to upper Oligocene strata; To, OligocUnits Tmm, Tml, Tmo, and To are assumed melange and broken formation equivalent to the Hoh rock assemblage of Rau (1975, 1979). Modified aftWagner (1982) and Snavely (1987).
Eocene Coal-Bearing Depositional Systems of Western Oregon and Washington 51

complex thin-skinned structure associated with these periods 

of deformation in southwestern Washington.

Eocene Coal-Bearing Depositional 

Systems of Western Oregon and 

Washington

Eocene coal-bearing rocks of western Oregon and Washington are included in a variety of stratigraphic units that bear 

different names in different parts of the Western Oregon and 

Washington Province. This abundance of stratigraphic names 

is a reflection of the many different but largely uncoordinated 

geologic investigations that have taken place in the various 

areas, as well as a consequence of the intertonguing relations 

in different areas between sedimentary rocks and intrabasinal 

volcanic rocks in the province. Despite the different names, 

it is important to recognize that all these stratigraphic units 

were deposited in a single regional coal-depositional system 

that extended north–south along depositional strike from the 

Bellingham area in northwestern Washington south to the 

Coos Bay area in southwestern Oregon (fig. 57) (Dott, 1966). 

At times, this regional depositional system was segmented by 

faults and local volcanic centers. Additionally, the intrabasinal 

Tukwila and Northcraft volcanic centers (Tukwila and Northcraft Formations, respectively, fig. 5) had important effects on 

the Washington part of the Eocene coal-bearing architecture 

and facies patterns (Buckovic, 1979). Paleobotanic studies (Wolfe, 1968, 1978, 1981, 1994, 1995; Burnham, 1994; 

Retallack and others, 2004) indicate that during the Eocene, 

the province coastal climate was warm, humid to mesic, and 

subtropical.

Eocene coal-bearing rocks of western Washington are 

included in a variety of stratigraphic units including the 

Carbonado, Chuckanut, Cowlitz, Renton, Skookumchuck, 

Spiketon, and Tiger Mountain Formations, and the undivided 

Puget Group (fig. 5) (Brownfield and others, 1994). In Oregon, 

coal-bearing units are the Bateman, Coaledo, Cowlitz, Spencer, and Tyee Formations and the Umpqua Group (fig. 8). 

Paleocurrent data indicate that sediment transport was 

from east to west across western Washington (Buckovic, 1979; 

Brownfield and others, 1994, 2005). Middle to upper Eocene 

sandstones are generally arkosic (Buckovic, 1979; Frizzell, 

1978; Johnson, 1985; Heller and Ryberg, 1983; Wells and 

others, 2000; Ryu, 2003), the source being crystalline rocks to 

the east; the proportion of volcanic detritus generally increases 

upward in the section, but also varies locally as a function of 

proximity to volcanic centers.

Coal-bearing formations in western Oregon and Washington were deposited in a variety of fluvial, deltaic, brackish, and shallow-marine environments (for example, Allen 

and Baldwin, 1944; Baldwin and others, 1973; Buckovic, 

1979; Armentrout, 1980; Burnham, 1990; Brownfield and 

others, 1994, 2005; Flores and Johnson, 1995). Fluvial and 

distributary channel deposits typically form thick crossbedded 

sandstone bodies. Interchannel deposits comprise a variety of 

sandstone, mudstone, and coaly facies deposited in crevasse 

channels and splays, floodbasins, shallow lakes, and mires. 

Shallow-marine and brackish-water deposits consist mainly 

of stratified to massive (from bioturbation) sandstone and 

mudstone deposited in tide- and wave-influenced shoreface, 

mouthbar, and shallow-shelf environments. Coals are bracketed by both nonmarine and brackish or shallow-marine facies 

and developed in both upper and lower delta and coastal-plain 

settings.

Following sedimentological models of Ryer (1984) for 

Cretaceous rocks in the Rocky Mountains, the general upward 

thinning of the coal beds exposed in the coal-bearing areas in 

Eugene

Coos Bay

Portland

Olympia

Bellingham

Mist gas

field

Coastal plain Coastal Plain

WASHINGTON

OREGON

Figure 57. Paleogeographic map showing the peat-bearing 

coastal plain of western Oregon and Washington during middle 

to late Eocene time. Feldspathic-quartzose sands, derived 

from eastern granitic terranes, were transported westward 

in several river systems to a broad coastal plain bordering a 

shelf-margin sea. Coal swamps developed from Bellingham 

to Coos Bay. Volcanism within the sediment source terrain, 

along the coastal margin, and on nearshore islands provided 

volcaniclastic sediments. Modified after Dott (1966) and 

Armentrout and Suek (1985).
52 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

the province is consistent with their deposition during a major 

transgressive pulse along the Eocene coastline of southwest 

Washington.

Tectonic Evolution of the Pacific 

Northwest

Paleomagnetic studies of lower Eocene to Miocene 

volcanic and sedimentary rocks in the Oregon and Washington Coast Range (fig. 58) demonstrate that this crustal block 

rotated from 75° to 80° clockwise with respect to the North 

American plate since the early Eocene (Simpson and Cox, 

1977; Heller and Ryberg, 1983; Wells and Coe, 1985; Wells 

and Heller, 1988; England and Wells, 1981; Wells and others, 

2000). This rotation of the Coast Range may still be occurring, with the extension of the northern part of the Basin 

and Range region (Wells and Heller, 1988; Wells and others, 

1998). The lower to middle Eocene Tyee Formation (fig. 12) 

is rotated about 67° clockwise (Simpson and Cox, 1977), and 

its onlap onto the Klamath terrane indicates that the rotation 

postdates the accretion of the Siletz terrane to the continent 

(Heller and Ryberg, 1983; Wells and others, 2000). Wells and 

others (2000) reported that the Paleogene Umpqua Group fold 

axis formed prior to the deposition of the Tyee Formation, 

therefore the 67° of rotation measured in the Tyee rocks must 

have occurred after the deformation of the Umpqua Group. 

The Eocene Tillamook Volcanics in the north-central Oregon 

Coast Range have been rotated clockwise about 46° (Magill 

and others, 1981), but volcanic rocks in the northern part of 

the Washington Coast Range were rotated much less. Samples 

from the lower Eocene Crescent Formation collected in the 

Black Hills west of Olympia, Wash., have measured clockwise 

rotations of about 27° (Globerman and others, 1982), and 

the Eocene volcanic rocks at Bremerton west of Seattle have 

measured clockwise rotations of about 7° (Beck and Engebretson, 1982). The middle Miocene flood basalts of the Columbia 

River Basalt Group are the youngest rocks with measured 

rotations; these show a clockwise rotation of 15° to 25° when 

compared to similar flows on the Columbia Plateau (Wells and 

Heller, 1988).

Several tectonic models have been proposed to explain 

the large Tertiary clockwise rotations of crustal blocks in the 

Pacific Northwest. The proposed models consist of three major 

rotation concepts or the combination of two or more of the 

concepts: (1) microplate rotation during accretion of allochthonous Coast Range marginal terranes (Simpson and Cox, 

1977; Duncan, 1982), (2) rotation induced by dextral shear 

between the continent and oceanic plates to the west (fig. 59) 

(Beck, 1976, 1980; Wells and Coe, 1985; Wells and Heller, 

1988), and (3) rotation of terranes in front of differential 

continental extension in the Basin-and-Range Province region 

(Simpson and Cox, 1977; Hammond, 1979). Wells and Heller 

(1988) proposed a two-fold model that incorporates both dextral shear and continental extension in the Basin-and-Range 

region with little or no clockwise rotation related to the accretion of the early Eocene oceanic plates. The majority of the 

eastward rotation postdates the accretion and deformation of 

the lower Eocene Siletz terrane against the North American 

plate. Paleogeographic reconstructions based on the Wells and 

Heller (1988) model are shown in figure 59.

The late middle to late Eocene was a transitional period 

representing the last phases of the episode of rifting and 

strike-slip faulting prior to initiation of Cascade-arc volcanism. During this time, basin subsidence slowed significantly 

and coal-bearing sedimentary units (fig. 57) were deposited 

in fluvial, deltaic, and shallow-marine environments over the 

western basement terranes.

Cretaceous-Tertiary Composite Total 

Petroleum System (500401)

A total petroleum system (TPS)—the Cretaceous-Tertiary 

Composite TPS—is defined within the Western Oregon and 

Washington Province (fig. 1) and was first defined during an 

assessment of gas resources in the Eastern Oregon and Washington Province by Brownfield (2008). The TPS boundary is 

defined on the basis of where potential reservoir and source 

rocks are known to exist or inferred to exist, and where hydrocarbon source-rock thermal maturities have reached a vitrinite 

reflectance (RO) of 0.5 percent or greater. Gas generated from 

potential source rocks is interpreted to have migrated into 

Paleocene to Miocene reservoir rocks.

As defined, the TPS most likely underlies much of 

the Eastern Oregon and Washington Province and extends 

westward under the Cascade Range (fig. 1) obscuring and 

(or) separating many of the stratigraphically equivalent basins 

containing potential Paleogene hydrocarbon source rocks in 

both Oregon and Washington. That part of the TPS, described 

and assessed by Brownfield (2008), includes thick successions 

of Cretaceous to Oligocene fluvial to deltaic arkosic sandstone 

and interbedded mudstone, carbonaceous shale, and coal. 

These strata are in (1) the Eocene Swauk, Manastash, Teanaway, Chumstick, and Roslyn Formations and the Oligocene 

Wenatchee and Ohanapecosh Formations in Washington; and 

(2) the Cretaceous Hudspeth and Gable Creek Formations, the 

Paleocene to Eocene “Herren formation” of Shorey (1976), 

and the Eocene to lower Oligocene Clarno Formation in 

Oregon.

The western part of the Cretaceous-Tertiary Composite TPS includes thick Paleogene fluvial to deltaic arkosic 

sandstone and interbedded mudstone, carbonaceous shale, and 

coal as much 20,000 ft thick (Johnson, 1985). These strata, 

although widespread, are primarily restricted to disconnected 

basins throughout the TPS area (Frizzell, 1978, 1979; Johnson, 

1982; Johnson, 1984a,b; Johnson, 1985; Johnson and Tennyson, 1995; Brownfield, 2008).

The Chuckanut Formation (fig. 5) in the Bellingham 

Basin and coal field (figs. 2 and 40) may be stratigraphically 
Tectonic Evolution of the Pacific Northwest 53

Cascadia

subductionu zone

A B

125°

45° 45°

120° 115° 110° 125° 120° 115° 110°

SCF

SAF

WF

BFZ

Columbia

Plateau

Idaho

batholith

Sierra

Nevada

Blue

Mts.

Basin and

Range

0

0 200 400 MILES

200 400 KILOMETERS

EXPLANATION

Lower Tertiary oceanic basalt and

 overlying marine sedimentary rocks

Thrust fault—Sawteeth on upper

 plate

Cenozoic volcanic rocks High-angle fault—Bar and ball on

 downthrown side

Mesozoic plutonic rocks

Cenozoic fold axes

Fault—Arrows show relative movement

Mesozoic and Paleozoic metamorphic

 rocks

Cascade arc

G r e at Vall ey

Klamath

Mts

SP

SB

CB

BP

BH SG

WH

TV

EI

OI

YB

TF

RB

WC2

WC3

PO

GV OF

HF

SV

SN

7

0

25

0

0

7

12

14

30

80

67

49

48 30 CF

70

16

36

16 28

27

20 52

46

53

Figure 58. Geologic provinces and paleomagnetic-rotation data of the Pacific Northwest. A, Geologic provinces 

of the Pacific Northwest, modified from King and Beikman (1974); SAF, SCF, BFZ, and WF represent San Andreas 

fault, Straight Creek fault, Brothers fault zone, and Wasatch fault, respectively. B, Tectonic rotations of rock units, 

in degrees, modified from compilations by Grommé and others (1986), Magill and others (1981), and Bates and 

others (1981); shaded arrows indicate 95 percent confidence limits on rotations. Washington locations: BP, Eocene 

volcanic rocks at Bremerton-Port Ludlow (Beck and Engebretson, 1982); BH, Eocene Crescent Formation, Black 

Hills (Globerman and others, 1982); WH, Eocene Crescent Formation, Willapa Hills (Wells and Coe, 1985); GV, 

upper Eocene Goble Volcanics (Beck and Burr, 1979; Wells and Coe, 1985); PO, Miocene Pomona Member, Saddle 

Mountains Basalt (Magill and others, 1982); OF, upper Eocene and Oligocene Ohanapecosh Formation of Bates 

and others (1981); SG, Miocene Snoqualmie and Grotto batholiths (Beske and others, 1973); SP, Eocene Sanpoil 

Volcanics (Fox and Beck, 1985). Oregon locations: TV, Eocene Tillamook Volcanics (Magill and others, 1981); EI, 

Eocene intrusions (Beck and Plumley, 1980); OI, Oligocene intrusions (Beck and Plumley, 1980); SV, Eocene Siletz 

River Volcanics (Simpson and Cox, 1977); TF, Eocene Tyee Formation (Simpson and Cox, 1977); RB, Paleocene 

basalt at Roseburg (Wells and others, 1985); YB, upper Eocene Yachats Basalt (Simpson and Cox, 1977); WC2, WC3, 

Oligocene and Miocene volcanic rocks of the western Cascade Range (Magill and Cox, 1980; Beck and others, 

1986); CF, Eocene and Oligocene Clarno Formation (Grommé and others, 1986); CB, Miocene Columbia River Basalt 

Group; and SB, Miocene Steens Basalt (Mankinen and others, 1987); California locations: HF, Lower and Upper 

Cretaceous Hornbrook Formation (Mankinen and Irwin, 1982); SN, Late Cretaceous Sierra Nevada batholith (Frei 

and others, 1984).
54 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

equivalent to the Swauk, Roslyn, and Chumstick Formations 

in eastern Washington (Johnson, 1985). Johnson (1984b) 

inferred a rapidly uplifted crystalline source area to the east, 

but the arkosic sandstone petrography of the Chuckanut 

Formation is similar to the Swauk, Roslyn, and Chumstick 

Formations (Frizzell, 1978; Johnson, 1984a; Johnson, 1985) 

indicating a probable connection between the basins. Frizzell 

(1978) also suggested that the Chuckanut and Swauk Formations (current outcrop areas) might have been joined, then 

later separated by the Straight Creek fault zone (fig. 38). Other 

equivalent or partly equivalent rocks to the Chuckanut Formation extend southward in western Washington and include the 

Puget Group (fig. 5) in the Green River coal field (fig. 2), the 

Carbonado Formation in the Wilkeson-Carbonado coal field, 

and the Cowlitz and Skookumchuck Formations (Vine, 1969; 

Johnson and others, 1997) in the Centralia-Chehalis coal 

field (fig. 2). The coal-bearing strata accumulated in intertidal 

and deltaic environments along a tidal-influenced delta plain 

(Brownfield and others, 1994, 2005; Flores and Johnson, 

1995).

The marginal marine Spencer Formation and the marginal marine and deltaic Coaledo Formation (fig. 8) (Beaulieu, 1971) may be equivalent, in part, to the middle Eocene 

to Oligocene Clarno Formation (Brownfield, 2008) and the 

“Herren formation” of Shorey (1976). The upper Eocene 

Spencer contains lignite, coal, and carbonaceous shale in the 

upper parts of the unit (Beaulieu, 1971). The middle to upper 

Eocene Coaledo Formation in the Coos Bay coal field (fig. 2) 

contains numerous coal beds (Brownfield, 1981). The upper 

middle Eocene Tyee Formation (fig. 5) in the southern part of 

Coos County, Oreg. (fig. 1), southeast of the Coos Bay coal 

field, contains coal beds in the Eden Ridge coal field (fig. 2) 

(Brownfield, 1981) and may be equivalent, in part, to the 

Clarno Formation (Beaulieu, 1971).

An events chart (fig. 60) for the Cretaceous-Tertiary 

Composite TPS graphically portrays the ages of source, seal, 

and reservoir rocks, as well as the timing of trap development 

and generation, migration, accumulation, and preservation of 

hydrocarbons.

21 37 16

15 Ma 37 Ma 50 Ma

P P P

10° 23° 28°

12°

27° 39%

43° 72%

(113 km)

17%

(225 km)

(335 km)

Colorado

Plateau

Colorado

Plateau

Colorado

Plateau

Lower Tertiary oceanic basalt and

 overlying marine sedimentary rocks

Cenozoic volcanic rocks

Mesozoic plutonic rocks

Mesozoic and Paleozoic metamorphic

 rocks

Tertiary, Mesozoic, and Paleozoic rocks,

 undivided

EXPLANATION

Figure 59. Continental reconstructions at 15, 37, and 50 Ma, based on paleomagnetic and geologic constraints. Rotation due 

to dextral shear (in boxes) was subtracted from western Oregon and Washington rotations before restoration of crustal blocks 

about Euler pole, P (Frei and others, 1984). Resultant block rotations are shown, along with amounts of northern Basin-andRange extension required to produce them. Component of Farallon plate motion parallel to continental margin shown in circle in 

kilometers per million years (Engebretson and others, 1985). Modified after Wells and Heller (1988).
Cretaceous-Tertiary Composite Total Petroleum System (500401) 55

Hydrocarbon source rocks include lacustrine shales in 

the Eocene Swauk and Chumstick Formations and coals in the 

Eocene Manastash, Naches, and Roslyn Formations within the 

eastern Washington part of the TPS (Brownfield, 2008). In the 

western Washington part of the TPS, the source rocks include 

the coal- and carbonaceous-shale-bearing Eocene Chuckanut, 

Huntingdon, Renton, Tiger Mountain, Spiketon, Carbonado, 

Skookumchuck, and Cowlitz Formations and the undivided 

Eocene Puget Group (fig. 5).

In the Bellingham Basin, the coal zone in Chuckanut and 

Huntingdon Formations was penetrated at depths ranging from 

1,700 to 3,700 ft in several exploration wells (fig. 38). In the 

Birch Bay No. 1 well (fig. 61), coals and shales above 6,000 

ft contain both Type-III and Type-IIB kerogens (Hurst, 1991; 

Lingley and von der Dick, 1991; Johnson and others, 1997) 

and several zones contain more than 6 percent total organic 

carbon (TOC). Rocks below 6,000 ft have Type-III kerogens 

and lower TOC values. Vitrinite reflectance (RO) values ranging from 0.5 to 0.6 percent have been reported from depths 

of 1,700 to 7,600 ft in the Bellingham Basin, and in outcrops 

of the Chuckanut Formation on the southern part of the basin 

RO is 0.74 percent (fig. 61). Porosity values in the Chuckanut 

Formation arkosic sandstones in the Birch Bay No. 1 well 

decreases from 26 percent at a depth of 1,000 ft to less than 10 

percent at a depth of 6,000 ft (Hurst, 1991), and measured permeabilities range from less that 1 millidarcy (mD) to 58 mD 

(Johnson and others, 1997). Good reservoir rocks are present 

in the well to a depth of 4,500 ft. The decrease in reservoir 

quality with depth is the result of diagenetic alteration of feldspars and lithic rock fragments.

The undifferentiated middle to upper Eocene Puget 

Group and the Tiger Mountain, Renton, Spiketon, and Carbonado Formations of the Puget contain coal and carbonaceous 

mudstone source rocks with RO values ranging from about 

0.35 to 2.0 percent (Walsh and Lingley, 1991). The underlying Raging River Formation (fig. 5) contains possible marine 

mudstone (Vine, 1969; Johnson and O’Connor, 1994) with 

total organic carbon (TOC) contents ranging from 0.8 to 

1.1 weight percent and RO values ranging from 1.18 to 4.01 

percent (fig. 62). These rocks crop out only at Tiger Mountain 

(figs. 41 and 62) and are inferred to underlie a major portion 

of the Puget Lowland (Stanley and others, 1992; Johnson 

and Stanley, 1995; Johnson and Tennyson, 1995; Johnson 

and others, 1997). Johnson and O’Connor (1994) reported 

that, although in the Tiger Mountain area these rocks are 

overmature, they may exist at depth to the west and generated hydrocarbons in the past. Enhanced maturation may have 

occurred adjacent to Eocene and younger intrusive centers that 

lie within or on the margins of the Puget Lowland (Esposito 

and Whitney, 1995).

Reservoir rocks include fluvial and distributary-channel 

sandstones in the middle to upper Eocene Tiger Mountain, 

Renton, Carbonado, and Spiketon Formations and undifferentiated Puget Group (Buckovic, 1979). Individual sandstone beds range in thickness from 10 ft to more than 200 ft 

and are bounded by flood-plain deposits including coal and 

?

1.8

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

65

146

208

245 E

E

E

E

M

M

L

L

L

L

Neogene

24

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

Figure 60. Events chart for the Cretaceous-Tertiary 

Composite Total Petroleum System in the Western 

Oregon and Washington Province. The petroleum 

system was first defined during the assessment 

of the Eastern Oregon and Washington Province 

(Brownfield, 2008). Light blue indicates rock units 

present; wavy line, unconformity. Age ranges of 

source, seal, reservoir, and overburden rocks and 

the time of trap formation and generation, migration, 

accumulation, and preservation of hydrocarbons 

shown in green and yellow. Queries indicate 

uncertainty. Modified after Brownfield (2008) to 

include the possible source rocks in the Upper 

Jurassic to Lower Cretaceous Myrtle Group and 

the Upper Jurassic to Lower Cretaceous Dothan 

Formation of southern Oregon. Geologic time scale in 

millions of years (m.y.). Plio, Pliocene; Mio, Miocene; 

Olig, Oligocene; Eoc, Eocene; Pal, Paleocene, L, Late; 

M, Middle; E, Early.
56 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

carbonaceous mudstone (Vine, 1969; Johnson and Stanley, 

1995). Sandstone reservoirs might be present at depths of as 

much as 10,000 ft (Johnson and O’Connor, 1994; Johnson and 

others, 1997). The reservoir sandstones are generally arkosic 

but contain lithic rock fragments that contribute to the loss of 

porosity due to alteration and compaction at depth.

North of Morton, Wash. (fig. 62), the middle Eocene 

Carbonado Formation (fig. 5) is about 3,900 ft thick and consists of nonmarine and shallow-marine rocks deposited within 

a tide-influenced delta. Potential gas-prone source rocks are 

shallow-marine mudstones, coals, and carbonaceous shales. 

Samples analyzed from a coal exploration borehole (fig. 62; 

Amoco WC-83-5) north of Morton, Wash., show RO values 

ranging from 0.96 to 1.69 percent (Johnson and Stanley, 

1995). Potential reservoir rocks in the Carbonado Formation 

consist of fine- to coarse-grained sandstone beds of fluvial origin and generally range in thickness from 15 to 65 ft but can 

be as much as 230 ft thick. No porosity and permeability data 

6 MILES

Pre-Tertiary rocks

Chuckanut Formation

Quaternary deposits

Wells with total

depth > 1,500 ft 

Fold axis

Fault

Gas seep

EXPLANATION

International boundary

6,042'

5,576'

10,892'

5,202'

7,977'

RO = 0.53, 7,600' 7,858'

7,365'

RO

 = 0.55,

4,000' AHEL

Birch Bay No. 1

9,126'

RO ~0.55, 4,200'

6,229'

RO = 0.45, 5,275'

6,008'

5,458'

6,180'

UNITED STATES

Strait of Georgia

49° 

Bellingham

Basin

Bellingham

14,789' CANADA

UNITED STATES

CANADA

Sumas

Mountain

123° 

San Juan Islands

San Juan Islands

RO = 0.55, 1,709'

RO = 0.74,

outcrop

Birch Point

Blaine

King Mountain area

0

0 6 KILOMETERS

Figure 61. Map showing geology and locations of exploration wells for the Bellingham Basin area, northwestern Washington. 

Petroleum wells in the United States are listed in McFarland (1983) or in addendum to McFarland available through the 

Washington Division of Geology and Earth Resources. Petroleum wells in Canada are listed in Mustard and Rouse (1994). 

Thermal maturity data (RO, mean vitrinite reflectance) are from Hurst (1991) and Walsh and Lingley (1991); values are from 

surface samples unless footage from adjacent well is listed. Modified after Johnson and others (1997).
Cretaceous-Tertiary Composite Total Petroleum System (500401) 57

8,648'

6,693'

Everett

Basin

7,270'

47°

5,069

RO = 0.64,

4,890'

48°

123°

Puget

Sound

Tacoma

Wilkeson

Quaternary

deposits

Tertiary sedimentary

rocks, mainly Eocene

Tertiary volcanic

rocks

Basin center

boundary

Coal exploration

borehole

Wells with total

depth greater than

3,000 ft

EXPLANATION

Pre-Tertiary

rocks

RO = 0.24 to 0.61

200 to 3,100'

RO = 0.40 to 0.60

1,600 to 4,100'

RO = 0.40 to 1.69

0 to 1,800'

11,002

5,959'

7,417'

5,408'

Straits of

Juan de Fuca

Whidbey

Island

9,675'

RO = 0.60, 9,600'

7,353'

RO

 = 0.45,

7,250'

TM

Seattle

Basin

Cascade Range

RO = 1.18 to 4.01

0 to 1,600'

AMOCO

WC-83-14

Tacoma

Basin

8,271

5,721'

CR

RO = 0.70 to 1.20

7,562

RO = 0.81, 7,170'

12,920'

RO = 1.24, 12,900'

n=7, oil shows

TD=6,023

P <37%

6,800'

RO = 0.60, 6,800

9,291

RO = 0.59, 1,240'

 0.76, 9,220'

RO = 0.66,

3,980' 

Seattle

Everett

Morton

Black

Diamond

Mount

Rainier

0

0 15 KILOMETERS

15 MILES

AMOCO

WC-83-5

Figure 62. Map showing geology and locations of exploration wells for 

the Puget Lowland, northwestern Washington. Petroleum wells are listed 

in McFarland (1983) or in addendum to McFarland available through the 

Washington Division of Geology and Earth Resources. Thermal maturity 

data (RO, mean vitrinite reflectance) are from Walsh and Lingley (1991), 

Johnson and O’Connor (1994), Johnson and Stanley (1995), and Johnson 

and others (1997); values are from surface samples unless footage 

from adjacent well is listed. CR, Carbon River area; TM, Tiger Mountain. 

Modified after Walsh and others (1987) and Johnson and others (1997).
58 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

are available, but outcrop samples are typically well cemented 

(Johnson and Stanley, 1995).

The middle to upper Eocene marine mudstone of the 

McIntosh Formation and shallow-marine to deltaic mudstone 

and coal and carbonaceous shale of the Skookumchuck and 

Cowlitz Formations are potential source rocks in the Chehalis 

Basin and the eastern part of the Grays Harbor Basin (fig. 63). 

These source rocks include marine shale, coals, and carbonaceous mudstones (Snavely and others, 1958; Armentrout and 

Suek, 1985; Moothart, 1992; Niem and others, 1994; Brownfield and others, 1994; Flores and Johnson, 1995). The organic 

matter is Type III and is gas prone. Marine mudstones west 

of Centralia, Wash. (fig. 63), have total organic carbon (TOC) 

values ranging from 0.5 to 1.25 percent and vitrinite reflectance (RO) values ranging from 0.4 to 0.5 percent (Moothart, 

1992). Armentrout and Suek (1985) reported that Skookumchuck Formation siltstone samples have TOC values ranging 

from 1.35 to 7.22 percent and coal samples have TOC values 

from 39.23 to 55.19 percent. Coals in the Skookumchuck and 

Cowlitz Formations were sampled from the surface to a depth 

of 10,000 ft; they range from lignite to subbituminous rank 

with RO values ranging from about 0.35 to 0.6 percent but can 

be slightly higher (fig. 63). Walsh and Lingley (1991) reported 

RO values ranging from 0.4 to 0.87 percent from samples collected from two wells (depth 4,080 and 9,540 ft, respectively) 

in the Chehalis Basin. Thermal maturity generally increases 

to the east and in close proximity to intrusives (Esposito and 

Whitney, 1995). Reservoir rocks include middle to upper 

Eocene fluvial- and distributary-channel arkosic sandstones of 

the Cowlitz and Skookumchuck Formations, and marine sandstones of the McIntosh Formation. The sandstone reservoirs 

are as thick as 170 ft and generally arkosic (Henricksen, 1956; 

Snavely and others, 1958; Wurden and Ford, 1976; Brownfield 

and others, 1994; Flores and Johnson, 1995). Wurden and Ford 

(1976) reported than Skookumchuck Formation sandstones in 

the Jackson Prairie gas storage wells (fig. 63) have porosities 

ranging from 28 to 40 percent at depths of 1,500 to 3,000 ft 

and permeabilities as high as 8,500 mD. The Skookumchuck 

sandstones are comparable to those reported from the Mist 

field of northwestern Oregon where gas is produced from 

Cowlitz Formation sandstones.

Interpretation of seismic data indicate the presence of 

possible marine strata at depths of 6,500–16,400 ft below the 

Chehalis Basin and north of Morton, Wash. (figs. 62 and 63), 

providing another possible source rock (Stanley and others, 

1994; Stanley and others, 1996; Krehbiel, 1993; Johnson 

and Stanley, 1995). Enhanced maturation of source rocks has 

occurred adjacent to intrusive centers within or on the margins 

of the AU area.

In the western Oregon part of the Cretaceous-Tertiary 

Composite TPS, potential source rocks are organic-rich mudstones and coal facies of the Eocene Umpqua Group and Tyee, 

Coaledo, Yamhill, Cowlitz, and Spencer Formations (fig. 8). 

Mudstone in the underlying pre-Tertiary melange terrane in 

the Klamath Mountains may be source rocks (Law and others, 

1984; Ryu and others, 1996; Ryu, 2008), with total organic 

carbon values greater than 1 percent (Ryu and others, 1996).

In the southern part of the Oregon Coast Range, potential source rocks in the Umpqua Group include carbonaceous 

mudstone or coal in the White Tail Ridge Formation and possibly mudstones in the Tenmile Formation (Niem and Niem, 

1990; Ryu and others, 1996; Ryu, 2008), although mudstones 

in the Tenmile Formation contain TOC values less than 1 

percent.

Source rocks in the Tyee Formation include coals and 

carbonaceous mudstones in the Baughman Member, with TOC 

values as much as 43 percent (Law and others, 1984). Niem 

and Niem (1990) reported that Tyee Formation coals and carbonaceous shales in the Eden Ridge coal field (fig. 2) contain 

TOC values of more than 50 percent and sufficient volatile 

organic matter (28 to 58 percent) to generate gas. The Tyee 

Mountain and Baughman Members of the Tyee Formation 

contain organic-rich mudstones ranging from less than 1 percent to about 2.5 percent TOC (Ryu and others, 1996). Organic 

matter is dominantly gas-prone Type III. The Eocene sequence 

is generally marginally mature for oil and immature for gas, as 

measured in surface samples, in which RO values are generally 

in the range of 0.5 to 0.8 percent (Law and others, 1984; Niem 

and Niem, 1990; Ryu and others, 1996; Ryu, 2008). Subsurface samples from five wells in the southern Oregon Coast 

Range have typical RO values of 0.45–0.66 percent (Niem and 

Niem, 1990; Ryu and others, 1996).

Modeling of burial history, thermal maturity, and timing of hydrocarbons was reconstructed for the Tyee forarc 

basin (fig. 13) using 45 measured sections and 11 oil and gas 

exploration wells (Ryu and others, 1996). Table 1 lists the 13 

oil and gas wells in the Roseburg quadrangle with depths up 

to 13,177 ft; see figure 9 for the locations of the wells (Wells 

and others, 2000). The model indicates that rapid deposition 

and burial of sediment probably began in the early Eocene 

with a short period of uplift in the latest Eocene (fig. 64). This 

uplift was followed by renewed subsidence during deposition 

of the Coos Bay Basin strata. During the middle Miocene, the 

southern Oregon Coast Range began a rapid uplift that slowed 

during the Pliocene and Pleistocene but continues today (Niem 

and others, 1992). The maturity model by Ryu and others 

(1996) indicates that (1) the lower part of the Umpqua Group 

could have entered the hydrocarbon generation window during 

the middle Eocene; and (2) the Tenmile Formation entered the 

generation window in the late Eocene, and at present the lower 

Umpqua and Tenmile have reached moderate levels of maturity (>0.07 RO percent). Also, at the present time, the White 

Tail Ridge and Camas Valley Formations of the Umpqua 

Group are within the generation window at depths ranging 

from 8,500 to 14,500 ft. However, source rocks in the overlying Tyee, Elkton, and Bateman Formations have not been 

buried deep enough to generate hydrocarbons.

Gas seeps (mainly biogenic) and two oil seeps (Niem 

and Niem, 1990) indicate the likely presence of mature source 

rocks within the Western Oregon and Washington Province; the oil seeps may be derived from sources in Mesozoic 
Cretaceous-Tertiary Composite Total Petroleum System (500401) 59

4,330'

RO = 0.35

OREGON

WASHINGTON

3,500'

6,650'

R0

 = 0.23

4.484'

6,143'

10,820'

8,446'

10,708',

R0 = 0.64, 7,000'

3,110' 6,500'

9,455' 3,720'

3,037'

4,010'

3,015'

4,034'

6,855'

R0

 = 0.47, 4,600'

6,608'

Pacific Ocean

DHU

CB

AB

Centralia

5,272'

6,908'

3,946'

CR

Willapa Bay

Nehalem

arch

Longview

Puget Lowland

Grays

Harbor

Nehalem

Basin

Mist gas

field

Grays Harbor Basin

R0 = 0.48

P = 10 to 20%

K = 0.4 to 6.2 mD

Jackson Prairie

gas storage

max. TD = 8,015'

R0 = 0.41

P = 28 to 40%

K <8,500 mD

at 2,540'

Black

Hills

uplift

WHU

Northcraft

Formation

Fault

EXPLANATION

Fold axis

Quaternary deposits and

 Tertiary sedimentary rocks

Tertiary volcanic

 rocks

Wells with total depth greater

 than 3,000 ft

46° 30'

124°00’

0 10 MILES

0 10 KILOMETERS

Figure 63. Map showing the geology and locations of exploration wells for the southern part of the Puget 

Lowland and the Centralia and Grays Harbor Basins, southwestern Washington. Geology (including selectively 

displayed faults and folds) is based on Wells (1981), Walsh and others (1987), and Walker and MacLeod (1991). 

Petroleum wells in Washington are listed in McFarland (1983) or in addendum to McFarland available through 

the Washington Division of Geology and Earth Resources. Thermal maturity data (RO, mean vitrinite reflectance), 

porosity (P), and permeability (K, in millidarcies, mD) are from Wurden and Ford (1976), Walsh and Lingley (1991), 

Moothart (1992), or Johnson and others (1997); values are from surface samples unless footage from adjacent 

petroleum well is listed. AB, Astoria Basin; CB, Chehalis Basin; DHU, Doty Hills uplift; WHU, Willapa Hills uplift. 

Modified after Johnson and others (1997).
60 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Table 1. Oil and gas exploration wells in the Roseburg 30 x 60 quadrangle, Douglas and Coos Counties, Oregon. See figure 9 

for location of wells.

[Well number from Niem and Niem (1990); well depth in feet]

Well 

number

Well 

name

Well 

depth Latitude Longitude

4 Amoco Weyerhaeuser F-1 4,428 43.406 123.837

5 Amoco Weyerhaeuser B-1 11,330 43.386 123.714

6 Sheldon C. Clark “Oakland well” 2,235 43.405 123.311

7 Mobil Oil Corp. Sutherlin Unit 1 13,177 43.434 123.238

8 Union Oil Co. Liles 1 7,002 43.362 123.506

9 Hutchins & Marrs Glory Hole 1 2,987 43.238 123.521

10 Community Oil & Gas Co. Scott 1 3,693 43.242 123.440

11 Diamond Drill Contracting Co. Hamilton Ranch Well 3 545 43.246 123.511

12 Diamond Drill Contracting Co. Hamilton Ranch Well 1 628 43.182 123.553

13 Diamond Drill Contracting Co. Hamilton Ranch Well 2 1,109 43.221 123.515

14 W. F. Kernin Well 1 3,900 43.217 123.417

14 F. W. Dillard unnamed 700 43.176 123.474

16 Uranium Oil & Gas Co. Ziedrich 1 4,368 43.051 123.657

0

5,000

10,000

15,000

20,000

25,000

30,000

100 90 80 70 60 50 40 30 20 10 0

Time (Ma)

Depth, in feet

Rock unit

Tyee Formation

Camas Valley Fm.

White Tail Ridge Fm.

Tenmile Fm.

Bushnell Rock Fm.

pre-Tertiary rocks

Bateman Fm.

Elkton Fm.

K Pa E O M P

100°F

200°F)

0.5 to 0.7 (Ro%)

0.7 to 1 (Ro%)

1 to 1.3 (Ro%)

Coos Bay

Basin strata

EXPLANATION

Umpqua Group

Figure 64. Burial history model for strata in the Tyee Basin using a composite section 

modified after Ryu and others (1992). Red dashed line represents time-temperature index 

curve. Formation thicknesses are from Ryu and others (1992). Thermal history is calculated 

using a steady state heat flow of 1.27°F per 100 ft. Maturity was derived from Lawrence 

Livermore National Laboratories Easy Percent RO. Time interval for calculation of maturity 

and expulsion is five. Expulsion is based on vitrinite reflectance (RO). K, Cretaceous; Pa, 

Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene.
Cretaceous-Tertiary Composite Total Petroleum System (500401) 61

mudstones in the Klamath melange terranes, including the 

Myrtle Group and Dothan Formation. These units probably are 

below the Umpqua Group and Tyee Formation in the southernmost part of the Roseburg quadrangle (fig. 9). Biogenic gas 

seeps in deltaic facies of the White Tail Ridge Formation of 

the Umpqua Group west of Roseburg, Oreg. (fig. 9), appear to 

be sourced by interbedded coal and carbonaceous mudstones 

(Ryu and others, 1996). 

Potential source rocks in the Coaledo Formation (fig. 8) 

include coal and mudstone interbedded with potential reservoir sandstones. Total organic carbon (TOC) in the Coaledo 

Formation mudstone is about 1.45 percent, according to Law 

and others (1984). The Umpqua Group and Tyee and Elkton 

Formations contain TOC values ranging from 0.4 percent to 

1.35 percent with one Tyee coal containing 36.61 percent TOC 

(Law and others, 1984). These units are all thermally immature for gas as indicated by outcrop samples, for which analyses show RO values between 0.32 percent and 0.61 percent 

(Newton, 1980; Law and others, 1984). Numerous gas and 

oil shows in exploration and water wells in the Coos Bay area 

indicate that an unidentified mature source is probably present; 

gas from the Pacific Petroleum Morrison No. 1 well contains 

0.15 percent “heavy fraction” (Olmstead, 1989) suggesting a 

thermogenic origin for some of the gas.

In west-central and northwestern Oregon, source rocks 

are mudstone or coal facies of the Tyee, Yamhill, Cowlitz, and 

Spencer Formations (figs. 6 and 8). Potential lean gas-prone 

mudstone source rocks may locally be in the Tyee Formation 

in the central Oregon Coast Range, but no data were available for this assessment. Locally thin, kerogen-rich, immature 

(RO of 0.3 percent) laminated “oil shales” are interbedded 

in the middle to upper part of the Yamhill Formation in the 

Tillamook Highlands near Tillamook, Oreg. (fig. 6) (Snavely 

and others, 1993a); the Yamhill Formation ranges in thickness 

from 490 to 820 ft. Eight beds, as much as 4 in. thick, were 

mapped and one analyzed sample contained 2.14 percent total 

organic carbon. The main kerogen-bearing section consists 

of feldspathic basaltic sandstone, siltstone, and lapilli tuff in 

the upper part of the section. These kerogen-rich beds may 

represent a condensed section deposited in a restricted marineshelf basin in structural lows interbedded with upper middle 

Eocene volcanics. Similar kerogen-rich beds crop out north 

of the Columbia River in southwestern Washington (Wolfe 

and McKee, 1968) and north of Grays Harbor (fig. 54) (Rau, 

1986).

Marine shale and thin coals and carbonaceous shale of 

the middle to upper Eocene Cowlitz Formation are the inferred 

source rocks (Armentrout and Suek, 1985; Niem and others, 

1994) for undiscovered accumulations in the northwestern part 

of Oregon. Organic matter in these rocks is Type-III kerogen and is gas prone. Coals are of lignite to subbituminous 

rank; RO is generally between 0.35 and 0.6 but can be slightly 

higher. RO of marine mudstone at the surface and shallow 

(<5,000 ft) subsurface is generally 0.4 to 0.5, with typical 

TOC values of 0.5 to 1.25 weight percent.

In the Mist gas field area (fig. 1), analyzed surface 

samples of mudstone from the Cowlitz Formation yield total 

organic carbon (TOC) values ranging from 0.39 to 1.07 weight 

percent (Armentrout and Suek, 1985) and average 0.68 percent, whereas subsurface samples of potential source rocks in 

the Mist gas field are lean with vitrinite reflectance (RO) values 

averaging 0.21 percent. The data indicate that the gas probably 

was not generated in place and must have migrated from zones 

of higher maturity. The arkosic sandstones of the Cowlitz 

Formation have porosities ranging from 14 to 41 percent, 

averaging 25 percent, and permeabilities ranging from 46 to 

1,500 millidarcies (mD) with an average of 200 mD (Armentrout and Suek, 1985). These sandstones are less susceptible to 

diagenetic alteration than the more lithic-bearing sandstones. 

Samples of the upper Eocene and Oligocene Keasey Formation (fig. 8) above the Cowlitz contain 0.18 to 0.91 percent 

TOC and RO values ranging from 0.16 to 0.31 percent (Law 

and others, 1984; Armentrout and Suek, 1985).

The upper Eocene Spencer Formation (fig. 8) contains 

potential source rocks consisting of coals and carbonaceous 

mudstone that correlate to the productive zones of the Cowlitz 

Formation in the Mist gas field (Van Atta and Thoms, 1993). 

Law and others (1984) reported that the Spencer Formation 

in the southern part of the Willamette Valley contains 4.48 

weight percent TOC and an RO value of 0.48 percent. Potential reservoir rocks in the Spencer Formation include arkosic 

sandstone beds ranging in thickness from 2 to 30 ft and have 

a cumulative thickness of about 200 ft (Schlicker, 1962). 

Analyzed samples contain porosity values ranging from 32.2 

to 41.5 percent and permeability values ranging from 184 

to 4,510 mD. Van Atta and Thoms (1993) reported a clean 

arkosic sandstone about 980 ft thick in the Humble Oil Miller 

No. 1 well about 70 mi south of Portland, Oreg., near Albany, 

Oreg. There was one gas discovery in the Spencer Formation 

in 1981 at the American Quasar Hickey 9-12 well in Linn 

County southwest of Portland, Oreg. (fig. 1) (Olmstead, 1989). 

Production continued for about five months and was then 

abandoned because the volume of gas became subcommercial.

Before 1979, the only conventional oil and gas production in the Western Oregon and Washington Province was in 

Washington: (1) in Whatcom County, near Bellingham, Wash. 

(fig. 61), where small amounts of gas were produced from the 

Chuckanut Formation below Quaternary gravels; and (2) west 

of Aberdeen, Wash. (fig. 54), where about 12,000 barrels of oil 

and associated gas were produced from 1957 to 1961. Currently, the only hydrocarbon production is from the Mist gas 

field in northwestern Oregon (fig. 1), which was discovered in 

May 1979 (Bruer, 1980). Through 2008, the field has produced 

about 65 BCFG from sandstone reservoirs in the Cowlitz 

Formation.

The abandoned Rattlesnake Hills gas field (Hammer, 

1934), southwest of Yakima, Wash., is in the eastern part of the 

Cretaceous-Tertiary Composite TPS (figs. 1 and 2). This field 

was discovered in 1913 and produced about 1.3 BCFG before 

it was abandoned in 1941 (McFarland, 1979). Production 

was from two vesicular basalt zones sealed by sedimentary 
62 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

interbeds less than 2,000 ft deep within the Columbia River 

Basalt Group. The gas probably was generated from the underlying Eocene coals (Johnson and others, 1993) and was mostly 

methane with about 10 percent nitrogen (Wagner, 1966). 

Johnson and others (1993) reported that the gas in the basalt 

aquifers was thermogenic.

Tertiary Marine Total Petroleum 

System (500402)

A second total petroleum system (TPS)—the Tertiary 

Marine TPS—is defined within the northwestern part of the 

Western Oregon and Washington Province (fig. 1). The TPS 

boundary is defined on the basis of where potential Tertiary 

marine and marginal-marine reservoirs and gas-prone source 

rocks are known to exist or inferred to exist. The TPS boundary includes the Tofino-Fuca Basin Gas, Western Washington 

Melange, Southwest Washington Miocene Sandstone, and the 

Astoria plays of Johnson and Tennyson (1995) and Johnson 

and others (1997).

In the northern part of the Tertiary Marine TPS, more 

than 28,000 ft of north-dipping Eocene to lower Miocene 

strata contain gas-prone source rocks (Niem and Snavely, 

1991). These source rocks are deeply buried Eocene marine 

mudstones in the offshore part of the Tofino-Juan de Fuca 

Basin (fig. 65) that contain Type-III kerogen and 0.3 to 1.2 

percent TOC (Snavely and others, 1980; Niem and Snavely, 

1991). A second potential source rock is marine mudstones in 

Eocene to Oligocene Ozette terrane and other melange units 

(fig. 5) (Snavely and Kvenvolden, 1989) containing TypeIII kerogen and 0.4 to 0.9 weight percent TOC. The Eocene 

melange units, which crop out in the Olympic Peninsula 

(figs. 46 and 65), lie beneath the Crescent thrust fault (Niem 

and Snavely, 1991) with the Eocene Crescent Formation and 

other Eocene strata in the overriding block (figs. 48 and 65). 

Vitrinite reflectance values range from 0.4 to 0.5 percent from 

surface and well samples (Snavely and others, 1980; Niem and 

Snavely, 1991). Higher thermal maturity is expected where 

these rocks are buried as deep as 25,000 ft to the north in the 

deeper parts of the Tofino-Juan de Fuca Basin. The upper 

Eocene to lower Miocene turbidite sandstones of the Twin 

River Group (fig. 5) are potential reservoir rocks (Snavely and 

others, 1980; Niem and Snavely, 1991), the best of which have 

porosities ranging from 20.4 to 24.6 percent and permeabilities 

ranging from 2 to 657 mD (Niem and Snavely, 1991).

Eocene to Oligocene Ozette terrane and Oligocene to 

middle Miocene Hoh rock assemblage (fig. 5) mudstones are 

possible source rocks and are inferred to exist through much of 

the western part of the TPS (figs. 50, 51, and 66). The Ozette 

and Hoh rocks contain 0.5 to 1.0 weight percent TOC and contain Type-III kerogen (Snavely and Kvenvolden, 1989). In the 

Grays Harbor area (fig. 67), the vitrinite reflectance (RO) values are about 0.5 percent at a depth of 5,100 ft; however, about 

15 miles to the north, RO values in outcrop samples range from 

0.87 to 1.98 percent (fig. 64). Snavely and Kvenvolden (1989) 

reported vitrinite reflectance values of about 0.6 percent for 

rocks at depths of 6,000 ft in the Ocean City area (fig. 67). 

The distribution of Ozette and Hoh source rocks has not been 

determined, but the Paleogene melange should extend down 

to the top of the subducting Juan de Fuca plate (at least 50,000 

ft). Marine-turbidite channel sandstones located in coherent structural blocks of the Ozette terrane and the Hoh rock 

assemblage are potential reservoir rocks. Palmer and Lingley 

(1989) reported that sandstone units in the Grays Harbor area 

(fig. 1) range from 10 to 100 ft in thickness and composite 

sandstone units are as thick as 140 ft (Lingley, 1995). Porosities are generally less than 25 percent and permeabilities are 

less than 100 mD (Palmer and Lingley, 1989).

The Oligocene Smuggler Cove formation, informally 

named by Niem and Niem (1985), and the lower and middle 

Miocene Astoria Formation (fig. 5) also contain potential 

source rocks with Type-III kerogen and 0.65 to 2.0 weight percent TOC. The source rocks are mostly thermally immature to 

marginally mature, but locally they might be thermally mature 

where subjected to heating from Miocene basaltic intrusions 

of the Columbia River Group. Law and others (1984) reported 

that one Astoria Formation sample yielded an RO value of 

0.65 percent and a mudstone of the informal Smuggler Cove 

formation yielded an RO value of 1.78 to 1.85 percent, making it thermally mature to overmature. Potential reservoirs 

include the marginal marine and deltaic sandstone of the 

Miocene Astoria and Montesano Formations (fig. 5). Palmer 

and Lingley (1989) reported that a 600-ft-thick Montesano 

Formation sandstone in the Grays Harbor area (fig. 67) averaged 28 percent porosity and 1 darcy (D) permeability. Several 

sandstone beds as much as 100 ft thick were encountered in 

drill holes penetrating the Astoria and Montesano Formations 

east of Aberdeen (fig. 54) indicating that potential reservoirs 

may exist at depth.

An oil-prone source rock yet to be determined must be 

present in the TPS because of the numerous oil seeps and the 

approximately 12,000 barrels of oil produced from the Hoh 

rock assemblage in one well near Ocean City, Wash., from 

1957 to 1961 (fig. 66) (McFarland, 1983; Palmer and Lingley, 

1989).

An events chart (fig. 68) for the Tertiary-Marine TPS 

graphically portrays the ages of source, seal, and reservoir rocks, as well as the timing of trap development and 

generation, migration, accumulation, and preservation of 

hydrocarbons.

Tertiary Coalbed Gas Total Petroleum 

System (500403)

A third total petroleum system (TPS)—the Tertiary 

Coalbed Gas TPS—is defined within the Western Oregon and 

Washington Province (fig. 1). The TPS boundary is defined 

on the basis of where Paleogene coal-bearing units are known 
Tertiary Coalbed Gas Total Petroleum System (500403) 63

to exist or inferred to exist, and where the coals and carbonaceous shales are less than 6,000 ft below the surface. The coals 

serve as both source and reservoir rock. Coals and carbonaceous shales at depths greater than 6,000 ft were not assessed 

due to the potential decrease in permeability that could affect 

coalbed-gas recovery. Gas resource potential within the coals 

can be enhanced by the entrapment of migrated gas from other 

source rocks such as interbedded carbonaceous shale.

The Tertiary Coalbed Gas TPS likely underlies much of 

the central part of the Western Oregon and Washington Province (fig. 1) and extends southward from the Canadian border 

to the Klamath Mountains of Oregon; it contains about 11.1 

million acres. The TPS includes all the Eocene coal-bearing 

rocks that were deposited in a regional coal-depositional 

system that extended north–south along depositional strike 

from the Bellingham area south to the Coos Bay area in southwestern Oregon (fig. 57) (Dott, 1966).

An events chart (fig. 69) for the Tertiary Coalbed Gas 

TPS graphically portrays the ages of source, seal, and reservoir rocks, as well as the timing of trap development and 

generation, migration, accumulation, and preservation of 

hydrocarbons.

In the Bellingham Basin (fig. 61), the Chuckanut Formation contains at least 15 coal beds ranging from 2 to about 

25 ft thick with the majority of the coals in the 2- to 4-ft 

range; at least seven beds range from 6 to about 25 ft thick 

(Jenkins, 1923, 1924; Beikman and others, 1961). Two main 

coal zones are in Whatcom and Skagit Counties, Wash.—the 

Thrust fault

48°

124°

CANADA

UNITED STATES

Strait of Juan de Fuca

Tofino-Juan de Fuca Basin

Pacific Ocean

Vancouver

Island

Olympic Peninsula

Port

Angeles

Victoria

Cape

Flattery

Discovery

Bay fault

Metchosin

Volcanics

3,009',

6,218',

7,158'

7,493'

3,490',

3,619'

8,519'

6,571'

8,462'

RO = 0.5

RO =

0.42 to 0.61

RO = 0.58

to 1.60

RO =

0.33 to

1.29

Wells with total

 depth > 3,000 ft

Gas seep

Pre-Tertiary rocks

Fold axis

Tertiary Ozette terrane Fault

 and melanged or broken

 rocks

Sedimentary rocks interbedded

 with the Crescent Formation

Eocene Crescent Formation

 and the Metchosin Volcanics

 on Vancouver Island

Quaternary deposits and

 Tertiary sedimentary rocks

EXPLANATION

0 15 MILES

0 15 KILOMETERS

A

A’

Figure 65. Map showing the generalized geology and oil and gas data for the northern part of the Olympic 

Peninsula, Washington, and Vancouver Island, Canada. Petroleum wells are listed in McFarland (1983) or in 

addendum to McFarland available through the Washington Division of Geology and Earth Resources. Geology 

is based on Tabor and Cady (1978a) and Niem and Snavely (1991). Thermal maturity data (RO, mean vitrinite 

reflectance) and location of gas seeps are from Snavely and Kvenvolden (1989) and Niem and Snavely (1991); 

RO values are from surface samples unless footage from adjacent well is listed. Cross section A–A’ shown in 

figure 48.
64 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Columbia River

124°30’

48°00’

47°00’

Olympic

 Mountains

Pacific

 Ocean

RO =

0.95 to 1.60 RO =

0.58 to 0.95

RO =

0.79 to

1.18

3,095'

4,403'

6,210',gs

6,880'

RO = 0.96 to

2.05

3,010'

5,988'

4,927'

Willapa

Bay

7,500'

Grays

Harbor

3,453' 3,120'

5,073'

5,015' 5,722',gs

5,600'

n = 7, max.

TD = 6,500'

os, gs 4,130'

4,035'

3,805'

Strait of Juan de Fuca

RO =

0.33 to 1.29

4,925'

Ocean City area

n = 17, max.

TD = 9,344'

R0

 = 0.53, 5,100',

12,000 barrels of oil

from 1957 to 1961

RO =

0.40 to

0.87

RO =

0.87 to

1.98

Jefferson

oil seep

Hoh River

hydrocarbon

area

EXPLANATION

Thrust fault, barbs on

 upper plate

 Wells with total

 depth > 3,000 ft

gs = Gas show

os = Oil show

Oil or gas

 seep 

Eocene Crescent Formation and

 overlying Holocene to Eocene

 rocks

Miocene to Eocene melange and 

 overlying Pliocene to Holocene

 rocks

Miocene to Eocene melange and

 low-grade metasedimentary rocks

0 20 MILES

0 20 KILOMETERS

Figure 66. Map showing generalized geology and oil and gas data for northwestern Washington. Petroleum wells are 

listed in McFarland (1983) or in addendum to McFarland available through the Washington Division of Geology and Earth 

Resources. Geology is based on Tabor and Cady (1978a) and Walsh and others (1987). Thermal maturity data (RO, mean 

vitrinite reflectance) and locations of seeps are from Snavely and Kvenvolden (1989) and Palmer and Lingley (1989); RO

values are from surface samples unless footage from adjacent well is listed. Modified after Johnson and others (1997).
?

EXPLANATION

Quaternary to Pliocene deposits

Miocene Astoria and Montesano

 Formations

Oligocene and Eocene

 sedimentary rocks

Eocene Crescent Formation,

 mainly basalt

Fold axis

Fault

Thrust fault, dashed where inferred,

 barbs on upper plate

Wells with total depth > 3,000 ft

0 10 MILES

0 10 KILOMETERS

124° 

47° 

Grays

Harbor

Willapa

Bay

3,737'

12,293' 4,699'

3,910'

4,927'

Pacific

Ocean

5,093'

5,038'

4,600'

?

3,240'

3,120' 3,453'

4,200'

n = 5, max.

TD = 5,000'

R0

 = 0.57, 2,280'

Ocean City area

n = 14, max.

TD = 9,344'

R0

 = 0.53, 5,100'

 0.6, 6,000’

3,946'

6,855'

6,608'

6,928'

7,005'

6,725'

3,000'

3,950'

3,663'

4,248'

n = 4, max.

TD = 3,452'

R o = 0.47, 4,600'

4,989'

3,015'

Figure 67. Map showing generalized geology and oil and gas data for southwestern Washington and the Grays 

Harbor area. Petroleum wells are listed in McFarland (1983) or in addendum to McFarland available through the 

Washington Division of Geology and Earth Resources. Geology (including selectively displayed faults and folds) is 

based on Snavely (1987) and Walsh and others (1987). Thermal maturity data (RO, mean vitrinite reflectance) are 

from Snavely and Kvenvolden (1989) and Palmer and Lingley (1989); RO values are from surface samples unless 

footage from adjacent petroleum well is listed. Modified after Johnson and others (1997).

Tertiary Coalbed Gas Total Petroleum System (500403) 65
66 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

?

1.8

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

66

146

200

251 E

E

E

E

M

M

L

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

Figure 68. Events chart for the Tertiary-Marine Total 

Petroleum System in the Western Oregon and Washington 

Province. Light blue indicates rock units present; wavy 

line, unconformity. Age ranges of source, seal, reservoir, 

and overburden rocks and the time of trap formation and 

generation, migration, accumulation, and preservation of 

hydrocarbons shown in green and yellow. Queries indicate 

uncertainty. Geologic time scale in millions of years (m.y.). 

Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; 

Pal, Paleocene, L, Late; M, Middle; E, Early.

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

66

146

200

251 E

E

E

E

M

M

L

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

1.8

Figure 69. Events chart for the Tertiary Coalbed Gas Total 

Petroleum System in the Western Oregon and Washington 

Province. Light blue indicates rock units present; wavy 

line, unconformity. Age ranges of source, seal, reservoir, 

and overburden rocks and the time of trap formation and 

generation, migration, accumulation, and preservation of 

hydrocarbons shown in green and yellow. Queries indicate 

uncertainty. Geologic time scale in millions of years (m.y.). 

Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; 

Pal, Paleocene, L, Late; M, Middle; E, Early.
Blue canyon coal zone at the base of the Chuckanut Formation 

and the Bellingham coal zone of the Chuckanut Formation 

(also known as the King Mountain coal zone). The Bellingham Basin coal beds, which crop out along the western 

flank of the Cascade Range, from Bellingham to the town 

of Glacier (fig. 3), are lenticular and range in apparent rank 

from subbituminous to anthracite; however, most of the coals 

are high-volatile C to B bituminous in apparent rank. Jordan 

Exploration Company (2002) reported individual coal beds 

ranging from 1 to 16 ft thick with at least seven beds from 6 

to 16 ft thick and a potential aggregate coal thickness of more 

than 90 ft. Historical mining reports stated that the coals were 

gassy. An increase in apparent rank to as high as anthracite can 

be observed from west to east with increasing proximity to the 

areas of higher heat flow associated with the Cascade Range 

volcanism (Walsh and Lingley, 1991).

The King Mountain coal zone identified in the subsurface 

north of Bellingham most likely correlates to the Bellingham 

Bay Member of the Chuckanut Formation (Johnson and others, 1997). This coal zone contains as many as eight coal beds 

averaging 5 ft thick, with no beds greater than 10 ft thick. 

The coal zone was penetrated at depths ranging from 1,700 

to 3,700 ft in several exploration wells. In the Birch Bay No. 

1 well (fig. 61), shales, carbonaceous shales, and coals above 

6,000 ft contain both Type-III and Type-IIB kerogens (Hurst, 

1991; Lingley and von der Dick, 1991; Johnson and others, 

1997), and several zones contain more than 6 percent total 

organic carbon (TOC). Rocks below 6,000 ft have Type-III 

kerogens and low TOC values.

Coal-bearing rocks in the subsurface in the northern part 

of the Bellingham Basin, north of Bellingham, have historically been correlated with the Chuckanut and Huntingdon 

Formations (figs. 5). These rocks may be present throughout 

the Bellingham Basin subsurface and into Canada (fig. 61).

Discontinuous and lenticular deposits of subbituminous 

to low-volatile bituminous coal are in Tertiary nonmarine units 

overlying pre-Tertiary rocks similar to those in the Glacier 

area south of Bellingham (fig. 38). These rocks have been 

correlated to the Chuckanut Formation in the Bellingham area. 

The coal beds, which range from less than 1 ft to as much as 

10 ft thick, crop out near the base of the Tertiary strata in the 

Coal Mountain area (figs. 38 and 40).

Upper middle Eocene and upper Eocene coal-bearing 

strata in the central and northern part of the Puget Lowland 

(figs. 38 and 62) (Beikman and others, 1961) belong to the 

undivided Puget Group (fig. 5) (Vine, 1969). Vine (1969) 

described coal distribution and reserves in the area, and compiled a 6,230-ft-thick stratigraphic section based on surface 

and shallow subsurface data. Fifty continuous and discontinuous beds of coal and carbonaceous shale are present in Vine’s 

(1969) section. Borehole data indicate that coal-bearing strata 

extend down section for at least several hundred meters below 

Vine’s (1969) section. In the Green River district (fig. 2), 

the Puget Group contains at least 16 major coal beds with 

a minimum cumulative thickness ranging from 73 to 90 ft; 

the coal-bearing strata is more than 6,300 ft thick. Coal rank 

ranges from subbituminous B to high-volatile A bituminous 

with most coals being high-volatile bituminous.

The Renton Formation (fig. 5) contains at least 10 coal 

beds with an aggregate mined thickness of at least 36 ft in a 

2,180-ft-thick coal-bearing interval. Impure or bone coal and 

carbonaceous shale partings add another 80 ft to the coalbearing interval.

The middle Eocene Carbonado and the upper Eocene 

Spiketon Formations of the Puget Group (fig. 5) contain coal 

and carbonaceous shale in the Wilkeson and Carbonado coal 

fields (fig. 2). The Carbonado Formation contains at least nine 

coal beds ranging in thickness from 2 to 8 ft. The coals are 

high-volatile A bituminous to low-volatile bituminous and are 

the most important coking coal deposits in Washington (Beikman and others, 1961).

The middle Eocene Skookumchuck Formation contains 

at least 13 coal beds with an aggregate thickness of about 88 

ft in a coal-bearing interval that is about 2,600 ft thick. Coals 

range from lignite to subbituminous B (Beikman and others, 1961). Mean vitrinite reflectance of surface coals in the 

Skookumchuck range from 0.35 to 0.40, and subsurface values 

range from 0.40 to 0.70.

There are differences in the sedimentology of correlative coal-bearing strata in western Washington. For example 

Skookumchuck Formation in the Centralia mine has a greater 

proportion of brackish and shallow-marine rocks; whereas, the 

undivided Puget Group in the Black Diamond area contains 

a greater proportion of fluvial and (or) distributary channel 

and overbank deposits (Brownfield and others, 1994). This 

contrast reflects the more outboard (southwest) location of 

the Centralia area (fig. 41). In addition, positive relief caused 

during the deposition of the Eocene Northcraft Formation 

(volcanic center), which lies due east of Centralia (fig. 44), 

may have deflected fluvial channels to more southern and 

northern routes and isolated the Centralia area from fluvial 

influence. Although depositional environments as interpreted 

from the Centralia area show some fluctuation, nonmarine 

rocks become more dominant upward within each Eocene section and the overall regional trend is progradational.

The middle to upper Eocene Cowlitz Formation (fig. 5) 

of southwestern Washington contains coal and carbonaceous 

shale in the upper part of the formation (Roberts, 1958); it 

contains an aggregate thickness of about 70 ft of coal in at 

least seven beds in a 500-ft-thick section in the southern part 

of the area. Coals range from lignite to subbituminous B, but 

generally the coals are subbituminous C and have mean vitrinite reflectance values of about 0.40.

Gas has been collected and analyzed from 12 wells in the 

Jackson Prairie Gas Storage area (fig. 63) from three Skookumchuck and one Lincoln Creek sandstone reservoirs and 

is biogenic (Wurden and Ford, 1976). Torrent Energy (2008) 

reported preliminary testing of coal gas content to range from 

about 15–86 standard cubic feet (scf) per ton, averaging more 

than 50 scf per ton. Based on coal thickness, extent, rank, and 

gas content, the coalbed methane potential was estimated to 

more than 400 billion cubic feet of gas (Torrent Energy, 2008)

Tertiary Coalbed Gas Total Petroleum System (500403) 67
68 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

The middle Eocene Coaledo Formation in the Coos Bay 

Basin of Oregon contains numerous coals and carbonaceous 

shale beds. At least seven major coal beds are known in the 

lower member of the Coaledo Formation that contain numerous shale and bone coal partings. At least seven more coal 

beds are also in the upper member, with the informal Beaver 

Hill bed (5 to 6 ft thick) containing the greatest potential 

resources (Baldwin and others, 1973; Mason and Hughes, 

1975). Many of the upper member coal beds contain shale and 

bone coal partings. Some of the historical producing mines 

were reported to contain gassy coals. The coals are subbituminous in rank and have heating values ranging from 9,260 

to 10,080 Btu per pound on an as-received basis (Allen and 

Baldwin, 1944); they are characterized by an average moisture 

content of 17 percent, average ash content of 8 percent, and 

less than 1 percent sulfur (Baldwin and others, 1973).

The Spencer Formation contains thin coal beds associated 

with sandstone and carbonaceous shale. Thin coals and carbonaceous shale are common in the lower and upper parts of the 

formation just southeast of Portland, Oreg. (Al-Azzaby, 1980; 

Van Atta and Thoms, 1993). Several thin subbituminous coal 

beds have been reported in the southern part of the Oregon 

Coast Range (Wells and others, 2000). Spencer Formation 

coals are subbituminous to lignite along the eastern part of the 

central and northern Oregon Coast Range. 

Assessment Units of Western Oregon 

and Washington Province

Three assessment units were defined within the Western 

Oregon and Washington Province in three total petroleum 

systems: (1) the Western Oregon and Washington Conventional Gas AU in the Cretaceous-Tertiary TPS, (2) the Tertiary Marine Gas AU in the Tertiary Marine TPS, and (3) the 

Eocene Coalbed Gas AU in the Tertiary Coalbed Gas TPS. 

Undiscovered gas resources were quantitatively estimated in 

each AU, and undiscovered oil resources were also quantitatively estimated in the Tertiary Marine Gas AU.

Hydrocarbon accumulations in the Western Oregon and 

Washington Conventional Gas AU and Tertiary Marine Gas 

AU are of the conventional type and were defined using the 

criteria established by Schmoker and Klett (1999). The gas 

accumulation in the Eocene Coalbed Gas AU is of the continuous type (unconventional) and was defined using criteria 

established by Schmoker (1999).

Based on a play concept (rather than an assessment unit 

concept), Johnson and Tennyson (1995) assessed the undiscovered hydrocarbons in seven conventional plays and three 

continuous (coalbed gas) plays within the Western Oregon and 

Washington Province. For the seven conventional petroleum 

plays (Johnson and Tennyson, 1995), a mean undiscovered 

hydrocarbon resource of 115.9 BCF (billion cubic feet) of 

gas and 19.3 MMB (millions of barrels) of oil was estimated. 

Mean estimated undiscovered gas resources from the three 

hypothetical coalbed-gas plays was 697.3 BCF (Johnson and 

Rice, 1995).

Western Oregon and Washington Conventional 

Gas Assessment Unit (50040101)

The Western Oregon and Washington Conventional Gas 

AU within the Cretaceous-Tertiary Composite TPS (fig. 70) 

is defined to include the area in which potential reservoir and 

source rocks are known to exist or inferred to exist and where 

hydrocarbon source rock thermal maturities have reached 

a vitrinite reflectance (RO) of 0.5 percent or greater. Gas 

generated from potential source rocks is interpreted to have 

migrated into lower to upper Eocene reservoir rocks. This AU 

is classified as frontier on the basis of the existence of at least 

one producing field in the AU (the Mist gas field).

The Western Oregon and Washington Conventional Gas 

AU likely underlies much of the central part of the Western 

Oregon and Washington Province (fig. 70) and extends southward from the Canadian border to the Klamath Mountains of 

Oregon; it contains about 11.1 million acres. The gas accumulations in this AU are of the conventional type and were 

defined using the criteria established by Schmoker and Klett 

(1999). 

An events chart (fig. 71) for the Western Oregon and 

Washington Conventional Gas AU graphically portrays the 

ages of source, seal, and reservoir rocks, and timing of trap 

development, generation, accumulation, migration, and preservation of hydrocarbons.

The Bellingham Basin (fig. 61) is the northernmost basin 

in the AU and extends into Canada. Only the United States 

part of the basin is assessed as part of this AU. The northwestern boundary extends into the Strait of Georgia and the Strait 

of Juan de Fuca to the Canadian border. The northeastern 

boundary is the uplifted pre-Tertiary basement rock complex, 

the eastern boundary is the western foothills of the Cascade 

Range, and the southern boundary is the Klamath Mountains 

of Oregon and extends offshore to the 3-mile limit of State 

waters in southwestern Oregon. From southwestern Oregon 

north to Puget Sound, the western AU boundary generally 

follows the eastern part of the Oregon and Washington Coast 

Ranges.

Northwest of Bellingham, Wash. (fig. 61), thermogenic 

gas has been sampled from old well casings and contains high 

levels of methane and nitrogen (McFarland, 1983; Hurst, 

1991). One abandoned well vented about 10,000 ft3 of gas per 

day (McFarland, 1983). Between 1988 and 1991 three wells 

were drilled in Bellingham Basin with depths ranging from 

4,422 to 9,126 ft and gas shows were reported from several 

sandstone and coal beds (Johnson and others, 1997).

Modeling of burial history, thermal maturity, and timing of hydrocarbons in the central part of the Western Oregon 

and Washington Conventional Gas AU by Armentrout and 
Suek (1985) indicated that maturation of Cowlitz Formation source rocks may have begun in the middle Oligocene 

(fig. 72). Modeling of burial history for the pre-Tertiary 

rocks, the Bushnell Rock Formation, and the lower part of 

the Tenmile Formation of the lower Eocene Umpqua Group 

in the southern Oregon Coast Range indicates that maturation 

of source rocks occurred as early as middle Eocene (fig. 73) 

(Ryu and others, 1996). In the central part of the Oregon Coast 

Range, modeling of the burial history of strata penetrated 

in the General Petroleum Long Bell No. 1 well (total depth, 

9,004 ft) indicates that Umpqua Group source rocks entered 

the hydrocarbon maturation window in the middle Eocene and 

that thermogenic gas generation began in the Oligocene when 

depth of burial exceeded 14,000 ft (fig. 74) (Ryu and others, 

1996).

In the northern part of the AU, the reservoirs are the 

lower to middle Eocene Chuckanut Formation and possibly 

the upper Eocene to Oligocene Huntingdon Formation fluvial 

and distributary channel arkosic sandstones that are as much 

as 200 ft thick (Johnson, 1982, 1984a,b). Porosity and permeability are marginal and probably decrease with depth because 

of the alteration of feldspar and lithic rock fragments (Johnson 

and others, 1997). Fluvial deposition that produced the thick 

Chuckanut Formation must have also produced thick deltaic 

and continental shelf facies, as yet not identified possibly 

because of being transported northward by strike-slip faulting to form an exotic terrane in the Gulf of Alaska. Johnson 

(1984c) postulated that transcurrent faulting that truncated the 

Chuckanut Formation corresponds to west- and northwesttrending faults on Vancouver Island. Traps are likely large 

WASHINGTON

OREGON

NEVADA

MT

IDAHO

CALIFORNIA

CANADA

Yakima

Spokane

Richland

Portland

Eugene

Columbia River

Pacific

 Ocean

Potholes 

 Reservoir

Banks 

Lake

Coeur 

d'Alene 

Lake

Lake 

Pend 

Oreille

Malheur 

Lake

Crater 

 Lake

Mist

gas field

§ ̈¦5

§ ̈¦84

§ ̈¦84

§ ̈¦82

§ ̈¦90

§ ̈¦90

0 60 KILOMETERS

0 60 MILES

P a c i f i c 

O c e a n

WA

OR

NV

MT

ID

CA

CANADA

Location map

125° 123° 121° 119° 117° 115°

42°

44°

46°

48°

50°

Coos 

Bay

Coos 

Bay

coal

field

Seattle

Bellingham

Olympic

Peninsula

Grays Aberdeen

Harbor

§ ̈¦5

American

Quasar

Hickey 9–12

Figure 70. Western Oregon and 

Washington Conventional Gas 

Assessment Unit located in western 

Oregon and Washington; boundary 

shown in blue. Boundary of Western 

Oregon and Washington Province 

shown in red; boundary of CretaceousTertiary Total Petroleum System shown 

in orange. Locations of the Coos Bay 

coal field shown as a solid brown oval 

and the Mist gas field shown as a solid 

red circle.

Assessment Units of Western Oregon and Washington Province 69
70 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

anticlines—for example Hurst (1991) calculated 5,000 acres 

of closure on an anticline penetrated by the AHEL Birch Bay 

No. 1 well (fig. 61)—and structural traps related to high-angle 

faults in the Bellingham Basin area (Johnson, 1982; Mustard 

and Rouse, 1994). Seals are fine-grained fluvial rocks but are 

generally lenticular, which could permit potential leakage 

from the reservoirs. Maximum burial and hydrocarbon generation was during the late middle to early late Eocene before the 

late Eocene folding and uplift (Johnson and others, 1997).

Within the central and southeastern parts of the Puget 

Lowland (fig. 62), reservoirs are (1) marine lithic-rich sandstones of the lower and middle Eocene Raging River Formation of the Puget Group and deeply buried equivalent units 

in the Seattle Basin; and (2) fluvial- and distributary-channel 

sandstones in the middle to upper Eocene Carbonado, Raging River, Renton, Spiketon, and Tiger Mountain Formations 

and the undifferentiated Puget Group. The fluvial sandstone 

units are generally arkosic with thicknesses ranging from 

10 to more than 200 feet. Petrographic data indicate that the 

sandstones are “tight” in the eastern part of the Puget Lowland (Johnson and others, 1997) due to alteration of feldspar 

and lithic rock fragments. Sandstone units analyzed from two 

cores near Black Diamond, Wash. (fig. 62), revealed porosities from 6 to 37 percent and permeability ranging from 1 

millidarcy to 2 darcies. Traps are most likely anticlines and 

fault blocks, like the large Kingston arch within the northern 

Seattle Basin (Johnson and others, 1994), and smaller complex 

structures such as those in the Black Diamond and Morton 

areas of the of the western Cascade Range (fig. 62). Similar 

structures may be present in the Everett and Tacoma Basins. 

Seals are fine-grained marine and nonmarine Eocene rocks and 

possibly Oligocene volcanic rocks. Maximum burial and the 

onset of hydrocarbon generation occurred in the late Eocene 

and Oligocene before Oligocene to Neogene folding and uplift 

(Johnson and others, 1997). Regional heat flow was elevated 

during the formation of the Cascade Range in the early Oligocene and Miocene, possibly accelerating hydrocarbon generation. Because of the ongoing tectonism in the Pacific Northwest, structural traps within the AUs have most likely formed 

before, during, and after hydrocarbon generation.

The southernmost part of the Puget Lowland and the 

Chehalis Basin (fig. 63) contain potential reservoir rocks in 

the middle to upper Eocene Cowlitz, Skookumchuck, and 

McIntosh Formations (fig. 5). The Cowlitz and Skookumchuck Formations contain fluvial, deltaic, and shallow-marine 

arkosic sandstones as much as 170 ft thick; sandstone reservoirs within the Jackson Prairie gas storage well (fig. 63) have 

porosities of 30 to 40 percent and permeabilities as high as 8.5 

darcies (Wurden and Ford, 1976). The Skookumchuck sandstones are comparable to those reported from the Mist gas field 

of northwestern Oregon (figs. 2 and 63), where hydrocarbons 

are produced from Cowlitz Formation sandstones. Turbidite 

sandstone reservoirs in the McIntosh Formation are as thick 

as 100 ft and have porosities of 10 to 20 percent and permeabilities less than 6.2 mD (Moothart, 1992). Porosity in these 

McIntosh reservoir rocks is degraded by the presence of clays, 

?

?

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

66

146

200

251 E

E

E

E

M

M

L

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

1.8

Figure 71. Events chart for the Western Oregon and 

Washington Conventional Gas Assessment Unit in the 

Western Oregon and Washington Province. Light blue 

indicates rock units present; wavy line, unconformity. Age 

ranges of source, seal, reservoir, and overburden rocks 

and the time of trap formation and generation, migration, 

accumulation, and preservation of hydrocarbons shown in 

green and yellow. Queries indicate uncertainty. Geologic 

time scale in millions of years (m.y.). Plio, Pliocene; Mio, 

Miocene; Olig, Oligocene; Eoc, Eocene; Pal, Paleocene, L, 

Late; M, Middle; E, Early.
0°

10°

50°

100°

150°

60 50 40 30 20 10 0

0

5,000

10,000

15,000

20,000

Age (ma)

Temperature, in degrees c

Depth, in feet

HYDROCARBON

GENERATION

WINDOW

U. Astoria Fm.

L. Astoria Fm.

Scappoose Fm.

Pittsburg Bluff Fm. Keasey Fm.

Upper Cowlitz Fm,

Middle Cowlitz Fm.

Lower Cowlitz Fm.

Pre-Cowlitz Fm.

TTI = 3

TTI = 160

Possible Cowlitz Formation

 source rock

Hydrocarbon generation

 window

EXPLANATION

Figure 72. Burial history model for strata 

in the northern part of the Willamette 

Valley, using the Lopatin model (Waples, 

1980). Green window represents the 

calculated hydrocarbon generation 

window. Possible source rocks in upper 

and lower parts of Cowlitz Formation 

shown in brown. Overlapping area 

represents potential source rocks within 

generation window. Rocks of the lower 

part of Cowlitz Formation entered the 

generation window at 33 million years 

before present (Ma) and rocks of the 

upper Cowlitz Formation entered the 

generation window at 3 Ma. Formation 

thicknesses are from Ryu and others 

(1992). TTI, time-temperature index. 

Thermal history (calculated using a 

steady state heat flow of 1.5°F per 100 

ft). Modified after Armentrout and Suek 

(1985).

0

5,000

10,000

15,000

20,000

25,000

100 90 80 70 60 50 40 30 20 10 0

Time (Ma)

Depth, in feet

K Pa E O M P Rock unit

Coos Bay

Basin strata

100°F

200°F

0.5 to 0.7 (Ro%)

0.7 to 1 (Ro%)

1 to 1.3 (Ro%)

Tyee Formation

Camas Valley Fm.

White Tail Ridge Fm.

Tenmile Fm.

Bushnell Rock Fm.

pre-Tertiary rocks

Umpqua Group

EXPLANATION

Figure 73. Burial history model for strata in the southern part of the Tyee Basin using 

the Twentymile measured section modified after Ryu and others (1992). Red dashed line 

represents time-temperature index curve. Formation thicknesses are from Ryu and others 

(1992). Thermal history is calculated using a steady state heat flow of 1.27°F per 100 ft. 

Maturity was derived from Lawrence Livermore National Laboratories Easy Percent RO. 

Time interval for calculation of maturity and expulsion is five. Expulsion is based on vitrinite 

reflectance (RO). K, Cretaceous; Pa, Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, 

Pliocene. Ma, millions of years before present.

Assessment Units of Western Oregon and Washington Province 71
72 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

zeolites, and calcite. Traps are most likely fault blocks similar 

to the Mist field (fig. 75), that is, small folds with shallow 

dipping limbs, and stratigraphic traps formed by nearshore or 

deltaic sandstone units enclosed by mudstone (Armentrout and 

Suek, 1985; Niem and others, 1994). As with the central and 

southeastern parts of the Puget Lowland, ongoing tectonism 

in the Pacific Northwest likely formed structural traps within 

this area of the Western Oregon and Washington Conventional 

Gas AU before, during, and after hydrocarbon generation. 

Seals are overlying fine-grained mudstones and siltstones of 

the Lincoln Creek Formation (fig. 5) and interbedded marine 

mudstones and siltstones associated with the McIntosh turbidites. Maximum burial and the onset of hydrocarbon generation occurred in the Miocene (Johnson and Tennyson, 1995). 

Regional heat flow was possibly elevated during the middle 

Miocene by local heating from the Miocene Columbia River 

Basalt Group (Esposito and Whitney, 1995).

The Cowlitz Formation reservoir in the Mist gas field 

(figs. 2 and 63) is the informal Clark and Wilson sandstone 

sequence (fig. 75) of the Cowlitz Formation (Armentrout and 

Suek, 1985), which has reported porosities ranging from 25 to 

36 percent and permeabilities of 20 millidarcies to about 7 darcies (Alger, 1985; Armentrout and Seek, 1985; Niem and others, 1994). The Clark and Wilson sandstone sequence is about 

600 ft thick in the field area and consists of fine- to mediumgrained arkosic shallow-marine sandstone and interbedded 

mudstone. Traps are complex and at least 13 compartmented 

gas pools are known (Armentrout and Suek, 1985). Traps 

consist of faulted anticlines, and seals are transgressive shales 

in the upper parts of the Cowlitz and Keasey Formations (fig. 

75). The Keasey Formation shales are tuffaceous, and the 

volcaniclastic material has been altered to montmorillonite, an 

expandable clay. Stratigraphic traps are present in the Cowlitz 

Formation and consist of thin sandstone encased in shale 

(Armentrout and Suek, 1985). The Clark and Wilson sandstone sequence is equivalent to a thick sandstone unit in the 

Spencer Formation south of the Mist gas field where Schlicker 

(1962) reported sandstone porosities ranging from 32 to 41 

percent and permeabilities from 184 mD to about 4.5 darcies. Thermal modeling indicates that maturation and onset of 

hydrocarbon generation of the Cowlitz Formation source rocks 

probably occurred in the Oligocene (fig. 72) (Armentrout and 

Suek, 1985). Regional heat flow was possibly elevated during the middle Miocene by local heating from the Miocene 

Columbia River Basalt Group.

Probable reservoir rocks in the central and southern part 

of the Western Oregon and Washington Conventional Gas AU 

are (1) fan-delta and shelf- or slope-channel sandstone of the 

Bushnell Rock Formation and fluvial and deltaic sandstones 

of White Tail Ridge Formation of the lower Eocene Umpqua 

Group (fig. 13) (Niem and others, 1992; Wells and others, 

2000), (2) shelf and slope arkosic sandstones of the upper 

and middle Eocene Tyee Formation, and (3) nonmarine and 

marine sandstones in the middle Eocene Coaledo Formation 

(fig. 8). Reservoir facies vary greatly in thickness and quality. 

The White Tail Ridge Formation sandstones have the highest 

reservoir potential (Ryu and others, 1996) and consist of deltafront sandstone units with porosities up to 17.0 percent and 

permeabilities as much as 154 millidarcies (Niem and Niem, 

1990; Ryu and others, 1996) and thicknesses ranging from 

a few feet to 30 ft. Traps are most likely early Tertiary folds 

and faults with possible stratigraphic traps associated with 

the shelf- and-slope channel sandstones. Seals are marine and 

nonmarine interbedded mudstones and siltstones. Some Tyee 

Basin sandstones in the Umpqua Group and Tyee Mountain 

Member of the Tyee Formation could be potential tight gas 

reservoirs because they have low porosity and permeability 

(Law and Spencer, 1993; Ryu and others, 1996). The General 

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

100 90 80 70 60 50 40 30 20 10 0

Time (Ma)

Depth, in feet

K Pa E O M P Rock unit

Coos Bay

Basin strata 100°F

200°F

0.5 to 0.7 (Ro%)

0.7 to 1 (Ro%)

1 to 1.3 (Ro%)

Tyee Formation

Umpqua Group

Siletz River Volcanics EXPLANATION

Figure 74. Burial history model for 

strata in the General Petroleum Long 

Bell No. 1 well (total depth, 9,004 ft) 

located in the central part of the Tyee 

Basin (see fig. 13); modified after Ryu 

and others (1992). Red dashed line 

represents time-temperature index 

curve. Formation thicknesses are from 

Ryu and others (1992). Thermal history is 

calculated using a steady state heat flow 

of 1.27°F per 100 ft). Maturity was derived 

from Lawrence Livermore National 

Laboratories Easy Percent RO. Time 

interval for calculation of maturity and 

expulsion is five. Expulsion is based on 

vitrinite reflectance (RO). K, Cretaceous; 

Pa, Paleocene; E, Eocene; O, Oligocene; 

M, Miocene; P, Pliocene. Ma, millions of 

years before present.
Petroleum Long Bell No. 1 well appears to be overpressured 

at a depth of 6,970 ft (Ryu and others, 1996). These potential 

tight-gas sandstone accumulations were not assessed.

Modeling of burial history, thermal maturity, and timing of hydrocarbon generation within the Tyee forarc basin 

(figs. 73 and 74) indicates that the lower part of the Umpqua 

Group could have entered the oil generation window during 

the middle Eocene, and the Tenmile Formation entered the 

oil generation window in the late Eocene, and both have now 

reached moderate levels of maturity (>0.7 RO percent). Today, 

the White Tail Ridge and Camas Valley Formations are within 

the oil window at depths ranging from 8,500 to 14,500 ft.

Gas seeps (mainly biogenic) and two oil seeps (Niem 

and Niem, 1990) indicate the presence of mature source rocks 

within the province; the oil seeps may be derived from sources 

in Mesozoic mudstones in Klamath melange terranes including the Myrtle Group and Dothan Formation. Biogenic gas 

seeps in deltaic facies of the White Tail Ridge Formation of 

the Umpqua Group west of Roseburg, Oreg. (fig. 9), appear 

to be related to interbedded coal and carbonaceous mudstones 

(Ryu and others, 1996).

The Western Oregon and Washington Conventional Gas 

AU currently has only one producing gas field, the Mist field. 

The AU is given a geologic probability of 1.0 because there 

is sufficient evidence that there are adequate reservoirs, traps, 

and seals (appendix A). The estimated minimum, mode, and 

maximum numbers of undiscovered gas accumulations are 1, 

8, and 70, respectively, and the estimated minimum, median, 

and maximum sizes of undiscovered gas accumulations are 3, 

10, and 300 BCFG, respectively.

The assessed mean undiscovered volumes in the Western 

Oregon and Washington Conventional Gas AU are 454 BCF 

of estimated conventional gas (table 2) and 1.0 million barrels 

of natural gas liquids (MMBNGL). The estimated mean size 

Reichold Columbia Co. No. 6

Sec. 10 - T6N - R5W

Reichold Columbia Co. No. 3

Sec. 10 - T6N - R5W

S 50° W S 50° E

Depth,

in feet

Depth,

in feet

1,000

1,000

1,000

2,000

2,000

2,000

3,000

1,000

2,000 2,000

R/D No. 2

R/D No. 1

R/D No. 1

Keasey Formation

Shale of the

Cowlitz Formation Shale of

the Cowlitz

Formation

–1,000 Subsea

Shale of

the Cowlitz

Formation

Clark and

Wilson sandstone

Clark and

Wilson sandstone Clark and

Wilson sandstone

Interbedded lower Narizian

sedimentary and volcanic rocks

of the Cowlitz Formation

gas

water

Unconformity

Unconformity

0

0

1,000 FEET

300 METERS

Figure 75. Northeast–southwest cross section through Reichold Energy Corporation Columbia County Nos. 

6 and 3 wells in the Mist gas field, west of Portland, Oregon, showing the trapping of hydrocarbons in the 

informal Clark and Wilson sandstone that resulted from faulting against the shales of the Cowlitz Formation, as 

well as from the unconformable relations with the overlying Keasey Formation. Modified after Bruer (1980) and 

Armentrout and Suek (1985). R/D, Redrill of Reichold Columbia Co. No. 3 (No. 1) and Reichold Columbia Co. No. 6 

(Nos. 1 and 2) development wells.

Assessment Units of Western Oregon and Washington Province 73
74 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

of the largest expected gas field is 85 BCFG, and the estimated 

gas volume (454 BCF) is about 20 percent of the total estimated mean of 2,214 BCF of gas in the Western Oregon and 

Washington Province.

Tertiary Marine Gas Assessment Unit (50040201)

The Tertiary Marine Gas AU within the Tertiary-Marine 

TPS lies in the westernmost part of the Western Oregon and 

Washington Province (fig. 76). Currently, there is no petroleum production within the AU, so it is categorized as being 

‘hypothetical.” However, as discussed below, there is sufficient evidence in the form of numerous gas and oil seeps as 

well as the past production of some 12,000 barrels of oil near 

Ocean City, Wash., to indicate the presence of mature source 

rocks, adequate reservoir and source rocks, and potential traps.

The hypothetical Tertiary Marine Gas AU includes thick 

successions of Paleogene marine sandstone and shale and 

fluvial to deltaic arkosic sandstone and interbedded mudstone, 

carbonaceous shale, and coal. The AU boundary is defined to 

include the areas in which potential Tertiary marine- and marginal-marine reservoirs and gas-prone source rocks are known 

to exist or inferred to exist and where hydrocarbon source 

rock thermal maturities have reached a vitrinite reflectance 

(RO) of 0.5 percent or greater. The hydrocarbon accumulations in this AU are of the conventional type and were defined 

using the criteria established by Schmoker and Klett (1999). 

Normal pressured gas generated from potential source rocks is 

interpreted to have migrated into Eocene to Miocene reservoir rocks. The TPS boundary includes the Tofino-Fuca Basin 

Gas, Western Washington Melange, Southwest Washington 

Miocene Sandstone, and the Astoria plays of Johnson and Tennyson (1995) and Johnson and others (1997).

The AU extends southward from the Canadian border 

in the Strait of Juan de Fuca, likely underlies the Olympic 

Peninsula in the northwestern part of Washington, and extends 

southward along the Washington coastal area to the northwestern part of the Oregon coastal area in the Western Oregon and 

Washington Province (fig. 76); it contains about 3.6 million 

acres.

An events chart (fig. 77) for the Tertiary Marine Gas AU 

graphically portrays the ages of source, seal, and reservoir 

rocks, and the timing of trap development, generation, accumulation, migration, and preservation of hydrocarbons.

In the northern part of the AU, more than 28,000 ft of 

north-dipping Eocene to lower Miocene strata contain gasprone source rocks (fig. 65) (Niem and Snavely, 1991). These 

rocks are most likely deeply buried Eocene marine mudstones 

Total Petroleum System (TPS) 

and Assessment Unit (AU)

Field 

Type

Total Undiscovered Resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Cretaceous-Tertiary Composite TPS

Western Oregon and Washington

Conventional Gas AU

Oil 0 0 0 0 0 0 0 0 0 0 0 0

Gas 79 403 1,000 454 0 1 2 1

Tertiary Marine TPS

Tertiary Marine Gas AU

Oil 2 9 45 15 3 14 70 22 0 1 4 1

Gas 34 195 646 249 1 5 17 6

Total Conventional Resources 2 9 45 15 116 612 1,716 725 1 7 23 8

Tertiary Coalbed Gas TPS

Eocene Coalbed Gas AU CBG 0 0 0 0 565 1,307 3,024 1,489 0 0 0 0

Total Continuous Resources 0 7020 0 0 565 1,307 3,024 1,489 0 0 0 0

Total Undiscovered 

Oil and Gas Resources 2 9 45 15 681 1,919 4,740 2,214 1 7 23 8

Continuous 

Resources

Conventional 

Resources

Table 2. Western Oregon and Washington Province assessment results.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked

estimates. For gas accumulations, all liquids are included as the NGL (natural gas liquids). Undiscovered gas resources are the sum of

non-associated and associated gas. F95 represents a 95 percent chance of at least the amount tabulated; other fractiles are defined similarly. 

TPS, total petroleum system; AU, assessment unit; CBG, coalbed gas. Gray shading indicates not applicable]

Table 2. Western Oregon and Washington Province assessment results.
Assessment Units of Western Oregon and Washington Province 75

located in the offshore part of the Tofino-Juan de Fuca Basin 

(figs. 48 and 65) and contain Type-III kerogen and 0.3- to 

1.2-percent total organic carbon (Snavely and others, 1980; 

Niem and Snavely, 1991). Potential reservoir rocks are upper 

Eocene to Oligocene turbidite sandstones of the Twin River 

Group (figs. 5 and 47) (Snavely and others, 1980; Niem and 

Snavely, 1991), in which the best reservoirs have porosities 

ranging from 20.4 to 24.6 percent and permeabilities ranging from 2 to 657 mD (Niem and Snavely, 1991). Turbidite 

sandstone beds can be as thick as 40 ft, with composite 

sandstone units having thicknesses as much as 400 ft. Possible stratigraphic traps include buried turbidite channels and 

sandstone beds; small fault-related structural traps may also be 

present. Seals consist of marine mudstones interbedded with 

the turbidite sandstone bodies. Thermogenic gas seeps have 

been identified in the northern part of the AU, indicating that 

the source rocks have reached maturity and generated hydrocarbons (fig. 65) (Snavely and Kvenvolden, 1989). Lingley 

(1986) reported that one gas seep flowed at the rate of 20 

thousand cubic feet of gas per day. Maturation and migration 

probably occurred in the Miocene, during maximum burial 

of the Juan de Fuca Basin strata, and the Ozette melange and 

other middle and upper Eocene units occur below the thrust 

fault (fig. 48). Migration was probably along faults and updip 

within the Twin River Group turbidite reservoirs.

Eocene to Oligocene Ozette terrane and Oligocene 

to middle Miocene Hoh rock assemblage (fig. 5) (Snavely 

and Kvenvolden, 1989) contain marine-turbidite channel 

WASHINGTON

OREGON

NEVADA

MT

IDAHO

CALIFORNIA

CANADA

Yakima

Spokane

Richland

Portland

Eugene

Columbia River

Pacific

 Ocean

Potholes 

 Reservoir

Banks 

Lake

Coeur 

d'Alene 

Lake

Lake 

Pend 

Oreille

Malheur 

Lake

Crater 

 Lake

Mist

gas field

§ ̈¦5

§ ̈¦84

§ ̈¦84

§ ̈¦82

§ ̈¦90

§ ̈¦90

P a c i f i c 

O c e a n

WA

OR

NV

MT

ID

CA

CANADA

Location map

125° 123° 121° 119° 117° 115°

42°

44°

46°

48°

50°

Coos 

Bay

Coos 

Bay

coal

field

Seattle

Bellingham

Olympic

Peninsula

Grays Aberdeen

Harbor

§ ̈¦5

0 60 KILOMETERS

0 60 MILES

Figure 76. Tertiary Marine Gas 

Assessment Unit in western Oregon 

and Washington; boundary shown in 

green. Boundary of Western Oregon 

and Washington Province shown in 

red. Location of the Coos Bay coal 

field shown as a solid brown oval and 

the Mist gas field shown as a solid 

red circle.
76 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

sandstones in coherent structural blocks that are possible 

reservoir rocks and are inferred to exist through much of the 

northwestern part of the Tertiary-Marine AU (figs. 50, 51, 

and 66). Palmer and Lingley (1989) reported that sandstone 

units in the Grays Harbor area (fig. 1) range from 10 to 100 

ft in thickness, and composite sandstone units are as thick as 

140 ft (Lingley, 1995). Porosities are generally less than 25 

percent and permeabilities are less than 100 mD (Palmer and 

Lingley, 1989). Potential traps in the Ozette terrane and Hoh 

rock assemblage include fault blocks and anticlines, as well as 

stratigraphic and fault-related traps within the underthrusted 

turbidites in the Olympic accretionary wedge (figs. 50 and 

56). Seal rocks are fine-grained rocks within the Ozette and 

Hoh sequences. Numerous oil and gas shows are reported in 

exploration wells, and several oil and gas seeps are along the 

northwestern Washington coast (figs. 65 and 66). Migration 

and generation of hydrocarbons within this part of the Tertiary 

Marine Gas AU most likely occurred from the Oligocene to 

the present, as the Ozette terrane and Hoh rock assemblage 

were continually being underthrusted beneath the continental margin. Migration of the hydrocarbons from the mature 

source rocks is upward and westward along faults (Snavely 

and Kvenvolden, 1989; Palmer and Lingley, 1989). The lower 

and middle Miocene Angora Peak, Youngs Bay, and Wickiup 

Mountain members of the Astoria Formation (fig. 5), informally named by Niem and Niem (1985), contain potential 

reservoir rocks. The deltaic Angora Peak member is as much 

as 1,000 ft thick and contains crossbedded, fine-grained 

arkosic sandstone and conglomerate. The Youngs Bay member 

is about 1,100 ft thick and contains thick beds of medium- to 

fine-grained sandstone beds. The Wickiup Mountain member 

is about 1,300 ft thick and contains friable fine-grained sandstone beds. The potential Astoria Formation reservoir rocks 

have porosities ranging from 26 to 35 percent and permeabilities of 92 to 270 mD (Niem and Niem, 1985). Potential reservoirs also include marginal marine and deltaic sandstone of 

the Montesano Formation (fig. 5). Palmer and Lingley (1989) 

reported that a 600-ft-thick sandstone in the Montesano in the 

Grays Harbor area (fig. 67) averaged 28 percent porosity and 

1 darcy permeability. Several sandstone beds as much as 100 

ft thick were encountered in drill holes penetrating the Astoria 

and Montesano Formations east of Aberdeen (fig. 54), indicating that potential reservoirs may exist at depth. Traps are most 

likely fault traps adjacent to normal or oblique-slip faults of 

post-Miocene age (Johnson and Tennyson, 1995). Other potential traps within the Miocene units include small anticlines 

associated with thrusting and possible stratigraphic pinchouts 

of submarine channels within the Astoria and Montesano Formations. Seals are fine-grained rocks within these formations. 

Migration and generation of hydrocarbons most likely began 

in the latest Miocene after potential Miocene reservoirs were 

deposited. Regional heat flow was possibly elevated during the 

middle Miocene by local heating from the Miocene Columbia 

River Group.

?

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

66

146

200

251 E

E

E

E

M

M

L

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

1.8

Figure 77. Events chart for the Tertiary Marine Gas 

Assessment Unit in the Tertiary-Marine Total Petroleum 

System in the Western Oregon and Washington Province. 

Light blue indicates rock units present; wavy line, 

unconformity. Age ranges of source, seal, reservoir, and 

overburden rocks and the time of trap formation and 

generation, migration, accumulation, and preservation of 

hydrocarbons shown in green and yellow. Queries indicate 

uncertainty. Geologic time scale in millions of years (m.y.). 

Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; 

Pal, Paleocene, L, Late; M, Middle; E, Early.
The presence of an unknown, oilprone source rock in the TPS is evidenced 

by numerous oil seeps and approximately 

12,000 barrels of oil produced from the Hoh 

rock assemblage in one well near Ocean 

City, Wash., from 1957 to 1961 (fig. 66) 

(McFarland, 1983; Palmer and Lingley, 

1989).

The AU is given a geologic probability 

of 1.0 because there is sufficient evidence 

that the AU has adequate reservoirs, traps, 

and seals (appendix B). The estimated 

minimum, mode, and maximum numbers 

of undiscovered gas accumulations are 1, 

5, and 30, respectively, and the estimated 

minimum, median, and maximum sizes of 

undiscovered gas accumulations are 3, 8, 

and 800 BCFG, respectively. The estimated 

minimum, mode, and maximum numbers 

of undiscovered oil accumulations are 

1, 2, and 10, respectively; the estimated 

minimum, median, and maximum sizes of 

undiscovered oil accumulations are 0.5, 1.3, 

and 130 MMBO. 

The USGS assessed mean undiscovered volumes in the Tertiary Marine Gas 

AU are 249 BCF of estimated conventional gas (table 2) and 6 MMBNGL. The 

estimated mean size of the largest expected 

gas field is 101 BCFG, and the estimated 

gas volume (249 BCF) is about 11 percent 

of the total estimated mean of 2,214 BCF of 

gas in the Western Oregon and Washington 

Province. The assessed mean undiscovered 

volume of oil is 15 MMBO with an estimated mean of 22 BCF associated gas and 

1 MMBNGL. The mean size of the largest 

expected oil field is 9 MMBO.

Eocene Coalbed Gas Assessment 

Unit (50040381)

The Eocene Coalbed Gas AU within 

the Tertiary Coalbed Gas TPS of the Western 

Oregon and Washington Province (fig. 78) is 

also classified as hypothetical because there are no currently 

producing fields. The coincident TPS and boundary is defined 

on the basis of where Paleogene coal-bearing units are known 

to exist or inferred to exist and where the coals and carbonaceous shales are less than 6,000 ft below the surface. The coals 

serve as both source and reservoir rocks. Coals and carbonaceous shales greater than 6,000 ft were not assessed due to the 

potential decrease in permeability that could affect coalbedgas recovery. Gas resource potential within the coals can be 

enhanced by the entrapment of migrated gas from other source 

rocks such as interbedded carbonaceous shale.

The hypothetical Eocene Coalbed Gas AU likely underlies much of the central part of the Western Oregon and 

Washington Province (fig. 78), extending southward from the 

Canadian border to the Klamath Mountains of Oregon; it contains about 11.1 million acres. The gas accumulations expected 

to be in this AU are of the continuous type (unconventional) 

WASHINGTON

OREGON

NEVADA

MT

IDAHO

CALIFORNIA

CANADA

Yakima

Spokane

Richland

Portland

Eugene

Pacific

 Ocean

Potholes 

 Reservoir

Banks 

Lake

Coeur 

d'Alene 

Lake

Lake 

Pend 

Oreille

Malheur 

Lake

Crater 

 Lake

Mist

gas field Columbia River

§ ̈¦5

§ ̈¦84

§ ̈¦84

§ ̈¦82

§ ̈¦90

§ ̈¦90

P a c i f i c 

O c e a n

WA

OR

NV

MT

ID

CA

CANADA

Location map

125° 123° 121° 119° 117° 115°

42°

44°

46°

48°

50°

Coos 

Bay

Coos 

Bay

coal

field

Seattle

Bellingham

Olympic

Peninsula

Grays Aberdeen

Harbor

§ ̈¦5

0 60 KILOMETERS

0 60 MILES

Figure 78. Eocene Coalbed Gas Assessment Unit in western Oregon and 

Washington; boundary shown in blue. Boundary of Western Oregon and 

Washington Province is shown in red. Locations of the Coos Bay coal field 

shown as a solid brown oval and the Mist gas field shown as a solid red 

circle.

Assessment Units of Western Oregon and Washington Province 77
78 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

100

200

50

150

250

Paleogene

Cretaceous

Jurassic

Triassic

Permian

66

146

200

251 E

E

E

E

M

M

L

L

L

L

Neogene

23

Pal

Eoc

Olig

Mio

Plio

? Basement rocks ROCK UNITS

SOURCE ROCK

RESERVOIR ROCK

SEAL ROCK

OVERBURDEN ROCK

TRAP FORMATION

PRESERVATION

GEOLOGIC

TIME SCALE

(m.y.)

PETROLEUM

SYSTEM EVENTS

GENERATION-MIGRATIONACCUMULATION

1.8

Figure 79. Events chart for the Eocene Coalbed Gas 

Assessment Unit in the Tertiary Marine Total Petroleum 

System in the Western Oregon and Washington Province. 

Light blue indicates rock units present; wavy line, 

unconformity. Age ranges of source, seal, reservoir, and 

overburden rocks and the time of trap formation and 

generation, migration, accumulation, and preservation of 

hydrocarbons shown in green and yellow. Queries indicate 

uncertainty. Geologic time scale in millions of years (m.y.). 

Plio, Pliocene; Mio, Miocene; Olig, Oligocene; Eoc, Eocene; 

Pal, Paleocene, L, Late; M, Middle; E, Early.

and were defined using the criteria established by Schmoker 

(1999).

An events chart (fig. 79) for the Eocene Coalbed Gas AU 

graphically portrays the ages of source, seal, and reservoir 

rocks, as well as the timing of trap development, generation, 

accumulation, migration, and preservation of hydrocarbons.

Within the Bellingham Basin (fig. 61) the Chuckanut 

Formation contains at least 15 coal beds ranging in thickness 

from 2 to about 25 ft (Jenkins, 1923, 1924; Beikman and others, 1961). Two main coal zones are in Whatcom and Skagit 

Counties, Wash.—the Blue Canyon coal zone at the base of 

the Chuckanut Formation and the Bellingham coal zone also 

in the Chuckanut Formation. Jordan Exploration Company 

(2002) reported individual coal beds ranging from 1 to 16 ft 

thick with at least seven beds with thicknesses ranging from 

6 to 16 ft and a potential aggregate coal thickness of more 

than 90 ft. In the Bellingham Basin-Whatcom County coal 

area (fig. 2), historical mining reports state that the coals were 

gassy. Over 95 old gas wells have been drilled in the Bellingham Basin (figs. 2 and 61) and most produced minor gas from 

Quaternary deposits-Chuckanut or Huntingdon Formation 

contact zone (Jordan Exploration Company, 2002). Only one 

desorbtion test has been reported for coals in the Bellingham 

Basin; it yielded 100 scf per ton (Johnson and others, 1997). 

Pappajohn (1991) reported four factors that are encouraging 

for the exploration of coalbed methane in the Bellingham 

area: (1) the presence of strata known to contain high-volatile 

bituminous coal at suitable depths with coalbed methane, (2) 

reports of methane in coal mining records, (3) the many gas 

shows from oil and gas wells penetrating the Eocene coalbearing strata, and (4) gas produced from shallow water wells 

trapped below the glacial deposits in the Ferndale gas field 

northwest of Bellingham.

The coalbed-gas sources in the Puget Lowland (fig. 44) 

and foothills of the western Washington Cascade Mountains 

are coals within the Puget Group and its Renton, Carbonado, 

and Spiketon Formations (fig. 5). The net coal thickness in the 

Puget Group is 90 ft in about 6,300 ft of section, and the coal 

rank ranges from subbituminous B to high-volatile A bituminous with most being high-volatile B bituminous (Vine 1969). 

The Renton Formation contains at least 10 coal beds in the 

Tiger Mountain area (fig. 62) with a net thickness of at least 

36 ft in a 2,180-ft-thick coal-bearing interval. The Carbonado 

Formation contains at least 16 coal beds, of which nine beds 

range from 2 to 8 ft thick, and the coals range in rank from 

high-volatile A bituminous to medium-volatile bituminous.

Fifteen exploration wells drilled since 1986 could be 

interpreted as coalbed-gas wells; a few wells were subjected 

to production testing (Pappajohn and Mitchell, 1991). Good 

gas shows were encountered in several wells, but there is 

presently no coalbed-gas production. Pappajohn and Mitchell 

(1991) reported desorbtion values ranging from 218 to 564 

scf per ton and averaging 423 scf per ton for five coalbeds 

penetrated by drilling in the Wilkeson area (fig. 62). Analyzed 

gas samples contained slightly less than 99 percent methane 

and minor amounts of nitrogen and carbon dioxide. Historical 
Assessment Units of Western Oregon and Washington Province 79

mining records accounts of underground mine accidents in the 

region related to methane and the presence of biogenic gas 

(δ13C = –71.11) bubbling to the surface through ponds in the 

John Henry No. 1 mine near Black Diamond, Wash. (fig. 62), 

reported by Brownfield and others (1994, 2005) are further 

indicators of gassy coals (Brownfield and others, 1994). 

Pappajohn and Mitchell (1991) reported analytical data that 

indicated that water produced from coal seams in the Wilkeson area meets State and Federal requirements for surface 

discharge.

In the Chehalis Basin area near Centralia, Wash. (fig. 63), 

the Skookumchuck Formation (fig. 5) contains gas-bearing 

coals as much as 40 ft thick. Duncan Oil Company, Inc. (2002) 

reported that desorbtion tests on coals recovered from the 

Duncan NWCH 42–9A well measured as high as 86 scf per 

ton in the 40-ft-thick Blue coal bed. Biogenic gas was collected and analyzed from 12 wells in the Jackson Prairie gas 

storage area from three sandstone reservoirs in the Skookumchuck Formation and one sandstone reservoir in the Lincoln 

Creek Formation (fig. 63). Torrent Energy (2008) also reported 

preliminary testing of coal-gas contents ranging from about 

15–86 scf per ton and averaging more than 50 scf per ton. 

Based on coal thickness, extent, rank, and gas content, the 

coalbed methane potential was estimated at more than 400 

BCFG for the Chehalis Basin (Torrent Energy, 2008).

In the Coos Bay coal basin (figs. 2 and 24), the lower and 

upper parts of the Coaledo Formation contain a net thickness 

of subbituminous to high-volatile bituminous coal of more 

than 100 ft. Torrent Energy (2008) reported that desorbtion 

tests of these coals yielded gas contents ranging from 60 to 

230 scf of gas per ton, averaging about 148 scf gas per ton. 

The gas has a methane content of about 99 percent. The coal 

beds have yielded permeabilities ranging from 4 to 15 mD and 

averaged about 8 mD (Smith, 2008). Eleven coalbed methane 

wells were drilled between 2005 and 2007, with five wells 

hydraulically fractured (fraced) and currently being production 

tested. The estimated total in-place coalbed gas is 1.2 trillion 

cubic feet (TCF) with a potential 400 BCF recoverable (Torrent Energy, 2008).

The Eocene Coalbed Gas AU currently has no producing 

gas fields. Because of the lack of well production data in this 

AU, the Fort Union Coalbed Methane AU (50330183) in the 

Wind River Basin, Wyoming (Johnson and others, 2007), was 

used as an analog to estimate total recovery for untested cells 

having potential for additions to reserves over the next 30 yr. 

The Eocene Coalbed Gas AU is producing gas from coalbeds.

The AU is given a geologic probability of 1.0 because 

there is sufficient evidence that the AU has adequate charge, 

reservoirs, traps, seals, and favorable geologic timing for an 

untested cell to contain the selected minimum of 0.02 BCFG 

(appendix C). The minimum, mode, and maximum number of 

acres with the potential for adding to reserves within the AU 

are 9,905,000, 11,095,000, and 12,205,000 acres, respectively 

(appendix C). The minimum, median, and maximum areas 

of the AU that are untested are all estimated at 100 percent 

(appendix C).

There are Eocene coals throughout the Eocene Coalbed 

Gas AU, with four geologic “sweet spot” areas: the Bellingham Basin (fig. 61), the southeastern Puget Lowland and foothills (fig. 62), the southernmost Puget Lowland and Centralia 

Basin area (fig. 63), and the Coos Bay Basin (fig. 24). The 

Bellingham Basin contains at least 15 coal beds ranging in 

thickness from 1 to 15 ft. Coalbed methane has been detected 

in several old exploration wells, and one coal sample was 

desorbed resulting in a yield of 100 scf per ton (Johnson and 

others, 1997).

The coalbed-gas sources in the southeastern Puget Lowland and foothills of the western Washington Cascade Range 

(fig. 62) are coals within the Puget Group, and the Renton, 

Carbonado, and Spiketon Formations (fig. 5). Net coal thickness in the Puget Group has a mean thickness of 90 ft (Vine, 

1969). The Renton Formation contains at least 10 coal beds 

in the Tiger Mountain area (fig. 62), with a net thickness of at 

least 36 ft. The Carbonado Formation contains at least 16 coal 

beds, of which nine beds range from 2 to 8 ft thick. Exploration wells, some of which were subjected to extended production testing, contained coalbed gas (Pappajohn and Mitchell, 

1991). Pappajohn and Mitchell (1991) reported desorbtion 

values ranging from 218 to 564 scf per ton, averaging 423 scf 

per ton (fig. 62).

In the southernmost Puget Lowland and Centralia Basin 

area of the Eocene Coalbed Gas AU, the Cowlitz, Skookumchuck, and Spencer Formations contain thick gas-bearing 

coals as much as 40 ft thick. Duncan Oil Company, Inc. 

(2002), reported that desorbtion tests on coals recovered from 

the Duncan NWCH 42–9A well as high as 86 scf per ton in the 

40-ft-thick Blue coal bed. Torrent Energy (2008) also reported 

preliminary testing of coal gas contents averaging more than 

50 scf per ton. Based on coal thickness, extent, rank, and gas 

content, the coalbed methane potential was estimated at more 

than 400 BCFG for the Chehalis Basin area (Torrent Energy, 

2008).

In the Coos Bay Basin (fig. 24), the lower and upper 

parts of the Coaledo Formation contain a net thickness of coal 

of more than 100 ft (fig. 26). Torrent Energy (2008) reported 

desorbtion test results for these coals that yielded gas contents averaging about 148 scf gas per ton. The estimated total 

in-place coalbed gas is 1.2 TCF with a potential 400 BCF 

recoverable (Torrent Energy, 2008).

The four “sweet spots” within the Eocene Coalbed Gas 

AU account for about 2,500,000 acres (22.5 percent) of the 

total 11,095,000 acres of the AU, and this percentage of acres 

was used to estimate the maximum area that remains for 

untested cells in the AU (second page of appendix C).

The estimated minimum, mode, maximum, and calculated mean percentages of untested area within the AU that 

has potential for additions to reserves in the next 30 years is 1, 

3.1, 22, and 8.7 percent, respectively (appendix C). A necessary condition to meet these estimates is that the total recovery 

per cell is equal to or greater than the minimum recovery per 

cell of 0.02 BCFG; it is likely that this amount of gas can be 

recovered from a majority of the untested cells in the AU. 
80 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

As previously discussed, the AU contains a thick section of 

coal-bearing strata with a continuous gas resource that were 

deposited in depositional settings similar to the analog Fort 

Union Coalbed Methane AU in the Wind River Basin, Wyoming (Johnson and others, 2007).

The minimum, median, and maximum total recovery for 

untested cells having potential for additions to reserves in the 

next 30 yr are 0.02, 0.1, and 2 BCFG, respectively (appendix 

C). These values were modified from similar values used in 

the analog AU; for example, the median value of 0.1 BCFG 

was about the same median value of 0.08 for the analog AU 

(Johnson and others, 2007), based on the presence of wells 

with shows of coalbed methane. These estimates for the total 

recovery for untested cells within the Eocene Coalbed Gas 

AU, however, assume that future production would be significantly greater in the next 30 yr.

The assessed mean undiscovered volume in the Eocene 

Coalbed Gas AU is 1,489 BCF of unconventional (continuous) 

gas (table 2), which is 67 percent of the estimated mean total 

of 2,214 BCF of gas within the Western Oregon and Washington Province that is presumed to be trapped in Tertiary coals of 

western Oregon and Washington.

Summary

The USGS assessed undiscovered, technically recoverable, conventional oil and gas and continuous (unconventional) coalbed gas in the Western Oregon and Washington 

Province, which includes about 40,000 mi2 of western Oregon 

and Washington (table 2), resulting in an estimated mean total 

of 2,214 BCFG and a mean of 15 MMBO. More than 67 percent of the total mean gas (1,489 BCFG) is contained within 

the hypothetical Eocene Coalbed Gas AU, which encompasses 

an area of more than 11 million acres. In this continuous AU, 

the Eocene coals, such as the coal-bearing Eocene Coaledo 

Formation, serve as both the source and reservoir rocks. The 

mean estimated volume of gas for the Western Oregon and 

Washington Conventional Gas AU is 454 BCFG, with an estimated mean size of the expected largest gas field of 85 BCFG. 

For the Tertiary Marine AU, the estimated mean volume of 

gas is 249 BCF, with an estimated mean size of the expected 

largest gas field of 101 BCFG. The assessed mean undiscovered volume of oil in the Tertiary Marine Gas AU is 15 

MMBO with estimated means of 22 BCF associated gas and 1 

MMBNGL. The mean size of the expected largest oil field is 

estimated at 9 MMBO.

Acknowledgments

The author thanks Wayne Husband for his numerous 

hours drafting many of the figures used in this manuscript, 

and Chris Anderson who supplied the Geographical Information System files for this assessment. The author also thanks 

Thomas Judkins, William Keefer, and Christopher Schenk 

for their suggestions, comments, and editorial reviews, which 

greatly improved the manuscript.

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90 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

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Appendix A. 91

Appendix A. Input parameters for the Western 

Oregon and Washington Conventional Gas 

Assessment Unit (50040101), Cretaceous-Tertiary 

Composite Total Petroleum System, Western Oregon 

and Washington Province
92 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

SEVENTH APPROXIMATION

DATA FORM FOR CONVENTIONAL ASSESSMENT UNITS (Version 6, 9 April 2003)

Assessment Geologist: Michael E. Brownfield Date: 2/24/2009

Region: North America Number: 5

Province: Western Oregon-Washington Number: 5004

Total Petroleum System: Cretaceous-Tertiary Composite TPS Number: 500401

Assessment Unit: Western Oregon and Washington Conventional Gas Number: 50040101

Based on Data as of:

Notes from Assessor: This frontier gas assessment unit is defined over a large area where 

potential reservoir and source rocks are known or inferred to coexist,

Mist gas field cumulative production - 65 BCF through 2008.

CHARACTERISTICS OF ASSESSMENT UNIT

Oil (<20,000 cfg/bo overall) or Gas (>20,000 cfg/bo overall): Gas

What is the minimum accumulation size? 0.5 mmboe grown (3.0 bcfg)

(the smallest accumulation that has potential to be added to reserves)

No. of discovered accumulations exceeding minimum size: Oil: Gas: 1

Established (>13 accums.) Frontier (1-13 accums.) 1 Hypothetical (no accums.)

Median size (grown) of discovered oil accumulations (mmbo):

1st 3rd 2nd 3rd 3rd 3rd

Median size (grown) of discovered gas accumulations (bcfg):

1st 3rd 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an undiscovered accum. > minimum size: 1.0

2. ROCKS: Adequate reservoirs, traps, and seals for an undiscovered accum. > minimum size: 1.0

3. TIMING OF GEOLOGIC EVENTS: Favorable timing for an undiscovered accum. > minimum 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

UNDISCOVERED ACCUMULATIONS

No. of Undiscovered Accumulations: How many undiscovered accums. exist that are > min. size?:

 (uncertainty of fixed but unknown values)

Oil Accumulations: minimum (>0) NA mode NA maximum NA

Gas Accumulations: minimum (>0) 1 mode 8 maximum 70

Sizes of Undiscovered Accumulations: What are the sizes (grown) of the above accums?:

 (variations in the sizes of undiscovered accumulations)

Oil in Oil Accumulations (m minimum NA median NA maximum NA

Gas in Gas Accumulations minimum 3 median 10 maximum 300

IDENTIFICATION INFORMATION
Appendix A. 93

AVERAGE RATIOS FOR UNDISCOVERED ACCUMS., TO ASSESS COPRODUCTS 

(uncertainty of fixed but unknown values) 

Oil Accumulations: minimum mode maximum

Gas/oil ratio (cfg/bo) NA NA NA

NGL/gas ratio (bngl/mmcfg) NA NA NA

Gas Accumulations: minimum mode maximum

Liquids/gas ratio (bliq/mmcfg) 0 2 4

Oil/gas ratio (bo/mmcfg) NA NA NA

SELECTED ANCILLARY DATA FOR UNDISCOVERED ACCUMULATIONS 

(variations in the properties of undiscovered accumulations) 

Oil Accumulations: minimum mode maximum

API gravity (degrees) NA NA NA

Sulfur content of oil (%) NA NA NA

Depth (m) of water (if applicable) NA NA NA

minimum F75 mode F25 maximum

Drilling Depth (m) NA NA NA NA NA

Gas Accumulations: minimum mode maximum

Inert gas content (%) 0.1 3.8 6

CO2 content (%) 0 0.002 0.02

Hydrogen-sulfide content (%) 0 0 0

Depth (m) of water (if applicable) 0 50 200

minimum F75 mode F25 maximum

Drilling Dep (m) 305 1,220 5,490

(ft) 1,000 4,000 18,000
94 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Appendix B. Input Parameters for the Tertiary 

Marine Gas Assessment Unit (50040201), Tertiary 

Marine Total Petroleum System, Western Oregon and 

Washington Province
Appendix B. 95

SEVENTH APPROXIMATION

DATA FORM FOR CONVENTIONAL ASSESSMENT UNITS (Version 6, 9 April 2003)

Assessment Geologist: Michael E. Brownfield Date: 2/24/2009

Region: North America Number: 5

Province: Western Oregon-Washington Number: 5004

Total Petroleum System: Tertiary Marine Number: 500402

Assessment Unit: Tertiary Marine Gas Number: 50040201

Based on Data as of:

Notes from Assessor: This hypothetical gas assessment unit is defined over a large area where 

potential reservoir and marine source rocks are known or inferred to coexist,

uncertainty in existence of adequate source and reservoir rocks and timing 

for hyrocarbon accumulation

CHARACTERISTICS OF ASSESSMENT UNIT

Oil (<20,000 cfg/bo overall) or Gas (>20,000 cfg/bo overall) Gas

What is the minimum accumulation size? 0.5 mmboe grown (3 bcfg)

(the smallest accumulation that has potential to be added to reserves)

No. of discovered accumulations exceeding minimum size: Oil: 0 Gas: 0

Established (>13 accums.) Frontier (1-13 accums.) Hypothetical (no accums X

Median size (grown) of discovered oil accumulations (mmbo):

1st 3rd 2nd 3rd 3rd 3rd

Median size (grown) of discovered gas accumulations (bcfg):

1st 3rd 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an undiscovered accum. > minimum size: 1.0

2. ROCKS: Adequate reservoirs, traps, and seals for an undiscovered accum. > minimum size 1.0

3. TIMING OF GEOLOGIC EVENTS: Favorable timing for an undiscovered accum. > minimum 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

UNDISCOVERED ACCUMULATIONS

No. of Undiscovered Accumulations: How many undiscovered accums. exist that are > min. size?:

 (uncertainty of fixed but unknown values)

Oil Accumulations: minimum (>0) 1 mode 2 maximum 10

Gas Accumulations: minimum (>0) 1 mode 5 maximum 30

Sizes of Undiscovered Accumulations: What are the sizes (grown) of the above accums?:

 (variations in the sizes of undiscovered accumulations)

Oil in Oil Accumulations (m minimum 0.5 median 1.3 maximum 130

Gas in Gas Accumulations minimum 3 median 8 maximum 800

IDENTIFICATION INFORMATION
96 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

AVERAGE RATIOS FOR UNDISCOVERED ACCUMS., TO ASSESS COPRODUCTS

(uncertainty of fixed but unknown values)

Oil Accumulations: minimum mode maximum

Gas/oil ratio (cfg/bo) 750 1,500 2,250

NGL/gas ratio (bngl/mmcfg) 25 50 75

Gas Accumulations: minimum mode maximum

Liquids/gas ratio (bliq/mmcfg) 12 25 38

Oil/gas ratio (bo/mmcfg) NA NA NA

SELECTED ANCILLARY DATA FOR UNDISCOVERED ACCUMULATIONS

(variations in the properties of undiscovered accumulations)

Oil Accumulations: minimum mode maximum

API gravity (degrees) 25 38 50

Sulfur content of oil (%) 0 0.3 1.5

Depth (m) of water (if applicable) 0 50 200

minimum F75 mode F25 maximum

Drilling Dep (m) 305 1,220 3,100

(ft) 1,000 4,000 10,000

Gas Accumulations: minimum mode maximum

Inert gas content (%) 0 2 10

CO2 content (%) 0 1.5 10

Hydrogen-sulfide content (%) 0 0.5 3.5

Depth (m) of water (if applicable) 0 50 200

minimum F75 mode F25 maximum

Drilling Dep (m) 305 2,600 6,100

(ft) 1,000 8,500 20,000
Appendix C. 97

Appendix C. Input Parameters for the Eocene 

Coalbed Gas Assessment Unit (50040381), Tertiary 

Coalbed Gas Total Petroleum System, Western Oregon 

and Washington Province
98 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Assessment Geologist: Michael E. Brownfield Date: 2/24/2009

Region: North America Number: 5

Province: Western Oregon-Washington Number: 5004

Total Petroleum System: Tertiary Coalbed Gas Number: 500403

Assessment Unit: Eocene Coalbed Gas Number: 50040381

Based on Data as of:

Notes from Assessor: This hypothetical gas assessment unit is defined over a large area where 

thick coal-bearing intervals are known to exist at depths less than 6,000 ft.

Coalbed methane has been observed in 4 areas within the AU.

Analog: Fort Union Coalbed Methane (Wind River Basin).

Assessment-unit type: Oil (<20,000 cfg/bo) or Gas (>20,000 cfg/bo), incl. disc. & pot. additions Gas

What is the minimum total recovery per cell? 0.02 (mmbo for oil A.U.; bcfg for gas A.U.)

Number of tested cells: 30 11 wells have been drilled with 5 wells being tested in Coos Bay, OR

Number of tested cells with total recovery per cell > minimum: 0

Established (discovered cells): Hypothetical (no cells): X

Median total recovery per cell (for cells > min.): (mmbo for oil A.U.; bcfg for gas A.U.)

 1st 3rd 2nd 3rd 3rd 3rd

Assessment-Unit Probabilities:

 Attribute Probability of occurrence (0-1.0)

1. CHARGE: Adequate petroleum charge for an untested cell with total recovery > minimum. 1.0

2. ROCKS: Adequate reservoirs, traps, seals for an untested cell with total recovery > minimum. 1.0

3. TIMING: Favorable geologic timing for an untested cell with total recovery > minimum. 1.0

Assessment-Unit GEOLOGIC Probability (Product of 1, 2, and 3): 1.0

1. Total assessment-unit area (acres): (uncertainty of a fixed value) 

calculated mean 11,095,000 minimum 9,905,000 mode 11,095,000 maximum 12,205,000

2. Area per cell of untested cells having potential for additions to reserves (acres): (values are inherently variable)

calculated mean 100 minimum 40 mode 80 maximum 180

uncertainty of mean: minimum 60 maximum 140

3. Percentage of total assessment-unit area that is untested (%): (uncertainty of a fixed value)

calculated mean 100 minimum 100 mode 100 maximum 100

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES

FORSPAN ASSESSMENT MODEL FOR CONTINUOUS

ACCUMULATIONS--BASIC INPUT DATA FORM (NOGA, Version 9, 2-10-03)

IDENTIFICATION INFORMATION

CHARACTERISTICS OF ASSESSMENT UNIT
Appendix C. 99

4. Percentage of untested assessment-unit area that has potential for additions to reserves (%):

( a necessary criterion is that total recovery per cell > minimum; uncertainty of a fixed value)

calculated mean 8.7 minimum 1 mode 3.1 maximum 22

Geologic evidence for estimates:

There are Eocene age coals throughout this AU with 4 areas (Bellingham, Southeastern Puget

Lowlands, Cowlitz–Spencer, and Coos Bay) that account for about 22.5 percent of the total

 assessment unit. These areas contain thick coals and coalbed methane is known to be 

present in all areas. Torrent Energy estimates that the Coos Bay area contains 1.2 TCF coal gas 

 with about 580 BCF of gas at a depth less than 4,000 ft.

Total recovery per cell for untested cells having potential for additions to reserves:

(values are inherently variable; mmbo for oil A.U.; bcfg for gas A.U.)

calculated mean 0.15 minimum 0.02 median 0.1 maximum 2

but unknown values)

Oil assessment unit: minimum mode maximum

 Gas/oil ratio (cfg/bo) NA NA NA

 NGL/gas ratio (bngl/mmcfg) NA NA NA

Gas assessment unit:

 Liquids/gas ratio (bliq/mmcfg) 0 0 0

TOTAL RECOVERY PER CELL

AVERAGE COPRODUCT RATIOS FOR UNTESTED CELLS, TO ASSESS COPRODUCTS

Assessment Unit (name, no.)

Eocene-Coalbed Gas (50040381)

 (Continued)

NO. OF UNTESTED CELLS WITH POTENTIAL FOR ADDITIONS TO RESERVES
100 Total Petroleum Systems and Geologic Assessment of the Western Oregon and Washington Province

Oil assessment unit: minimum mode maximum

 API gravity of oil (degrees) NA NA NA

 Sulfur content of oil (%) NA NA NA

 Depth (m) of water (if applicable) NA NA NA

 Drilling depth (m)

minimum F75 mode F25 maximum

Gas assessment unit: minimum mode maximum

 Inert-gas content (%) 0.01 0.30 2.00

 CO2 content (%) 0.01 1.80 8.00

 Hydrogen sulfide content (%) 0.00 0.00 0.00

 Heating value (BTU) 850 950 1050

 Depth (m) of water (if applicable)

 Drilling depth (m)

minimum F75 mode F25 maximum

152 305 1,829

 Drilling depth (ft)

minimum F75 mode F25 maximum

500 1,000 6,000

Success ratios: calculated mean minimum mode maximum

Future success ratio (%) 28 10 25 50

Historic success ratio, tested cells (%) About 1/2 of Steve Roberts Fort Union Analogs

used in the North Slope Assessment

Completion practices:

1. Typical well-completion practices (conventional, open hole, open cavity, other)

2. Fraction of wells drilled that are typically stimulated

3. Predominant type of stimulation (none, frac, acid, other)

4. Fraction of wells drilled that are horizontal

Assessment Unit (name, no.)

Eocene-Coalbed Gas (50040381)

SELECTED ANCILLARY DATA FOR UNTESTED CELLS

(values are inherently variable)

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