RI 33: Late Pleistocene Stratigraphy in the South-Central Puget Lowland

Home , Late Pleistocene, Puget Sound, Vashon Glaciation

Late Pleistocene Stratigraphy in the South-Central Puget Lowland, Pierce County, Washington RESOURCES

by Richard K. Borden and Kathy Goetz Troost

WASHINGTON

NATURAL DIVISION OF GEOLOGY AND EARTH RESOURCES Report of Investigations 33 December 2001

Location of study area

Late Pleistocene Stratigraphy in the South-Central Puget Lowland, Pierce County, Washington

by Richard K. Borden and Kathy Goetz Troost

WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Report of Investigations 33 December 2001 DISCLAIMER Neither the State of Washington, nor any agency thereof, nor any of their em- ployees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or other- wise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the State of Washington or any agency thereof.

WASHINGTON DEPARTMENT OF NATURAL RESOURCES Doug Sutherland—Commissioner of Public Lands

DIVISION OF GEOLOGY AND EARTH RESOURCES Ron Teissere—State Geologist David K. Norman—Assistant State Geologist

This report is available from: Publications Washington Division of Geology and Earth Resources PO Box 47007 Olympia, WA 98504-7007 Phone: (360) 902-1450 Fax: (360) 902-1785 E-mail: [email protected] Website: http://www.wa.gov/dnr/htdocs/ger/

Front Cover: Former Woodworth quarry on Hylebos Waterway, Tacoma. Photo by K. Troost, 1995.

Back Cover: Abandoned quarry on Hylebos Waterway, Tacoma. Photo by K. Troost, 1999.

Printed on recycled paper. Printed in the United States of America

ii Contents

Abstract ...... 1 Introduction...... 1 Stratigraphic nomenclature ...... 1 Recent investigations in the study area ...... 4 Field and laboratory procedures ...... 4 Glacial and nonglacial deposition in the Puget Lowland ...... 5 Nonglacial deposits ...... 5 Glacial deposits ...... 6 Differentiating glacial and nonglacial sediments ...... 7 Results ...... 8 Hylebos Waterway measured sections ...... 8 Route 7 measured section...... 9 Tacoma boathouse measured section ...... 10 Sunset Beach measured section ...... 11 Solo Point measured section ...... 11 Subsurface data...... 11 Discussion ...... 12 Vashon Drift ...... 12 Olympia beds...... 17 Pre-Olympia drift ...... 17 Second nonglacial deposits ...... 17 Third glacial drift ...... 19 Third nonglacial deposits ...... 19 Hydrogeologic implications...... 20 Conclusions ...... 21 Acknowledgments ...... 21 References cited ...... 21

APPENDICES Appendix A. Borehole summary ...... 24 Appendix B. Boreholes with radiocarbon data ...... 27

FIGURES Figure 1. Puget Lowland and study area ...... 2 Figure 2. Borehole and cross section location map ...... 4 Figure 3. Locations of radiocarbon samples ...... 5 Figure 4. Modern Puget Lowland depositional environments ...... 6 Figure 5. Location map of Puget Lowland river sediment samples ...... 6 Figure 6. Woodworth quarry composite measured section ...... 9 Figure 7. Manke quarry measured section ...... 9 Figure 8. Foran quarry measured section ...... 10 Figure 9. Route 7 measured section...... 10 Figure 10. Tacoma boathouse measured section ...... 10 Figure 11. Sunset Beach measured section ...... 11 Figure 12. Solo Point measured section ...... 11 Figure 13. Cross section A–A¢ ...... 12 Figure 14. Cross section B–B¢ ...... 13 Figure 15. Cross section C–C¢ ...... 13 Figure 16. Cross section D–D¢ ...... 14 Figure 17. Cross section E–E¢ ...... 14

iii Figure 18. Paleotopographic map of the base of the Vashon Drift...... 15 Figure 19. Paleotopographic map of the top of the pre-Olympia drift...... 16 Figure 20. Isopach map of the pre-Olympia drift ...... 16 Figure 21. Paleotopographic map of the top of the second nonglacial deposits ...... 18 Figure 22. Isopach map of the second nonglacial deposits ...... 18 Figure 23. Paleotopographic map of the top of the third glacial drift ...... 19 Figure 24. Paleotopographic map of the top of the third nonglacial deposits...... 20 Figure 25. Generalized stratigraphic and hydrostratigraphic column for west-central Pierce County ...... 20 Figure B-1. Borehole DA-2c,d ...... 28 Figure B-2. Borehole DA-12e ...... 29 Figure B-3. Borehole 4/6 Composite ...... 30 Figure B-4. Borehole LF4-MW12B ...... 31

TABLES Table 1. Puget Lowland stratigraphic nomenclature ...... 3 Table 2. Sediment characteristics of selected Puget Lowland rivers ...... 7 Table 3. Summary of radiocarbon data ...... 8

iv Late Pleistocene Stratigraphy in the South-Central Puget Lowland, Pierce County, Washington

Richard K. Borden Kathy Goetz Troost Kennecott Utah Copper Corporation University of Washington 8315 West 3595 South Department of Earth and Space Sciences PO Box 6001; Magna, UT 84044 Box 351310; Seattle, WA 98195

ABSTRACT Two distinct sets of late Pleistocene stratigraphic nomenclatures have been developed for the Puget Lowland, Washing- ton: one to the north of the Seattle area and one to the south. The simple sequence that was previously identified in the south-central lowland requires expansion and modification to correlate with the more complex but better-defined northern sequence. We confirm the presence of at least one additional glacial–nonglacial interval within the south-central lowland late-Pleistocene sequence. Numerous boreholes and detailed measured sections with radiocarbon dates confirm this stratigraphic interpretation. The inferred base of the uppermost unit in the sequence, the Vashon Drift, is sometimes represented by fine-grained glaciolacustrine deposits with an average age of 13,430 yr B.P. This date is about 1,000 years younger than is generally assumed for the inception of the Vashon Stade of the Fraser Glaciation in the southern lowland, but is consistent with Vashon recessional dates reported from elsewhere in the lowland. This implies either (1) that most of the Vashon sediments present in the study area are recessional in age or (2) that Vashon glaciation in the south-central lowland began much later than is commonly believed based upon numerous limiting dates in the northern lowland. Thin, discontinuous, nonglacial deposits exposed immediately beneath the Vashon Drift have been dated at 17,000 to >46,000 yr B.P. These newly identified nonglacial deposits are termed the “Olympia beds” and are correlative by age and character with sediments deposited during the Olympia climatic interval, which generally corresponds to oxygen isotope stage 3. The widespread, newly recognized glacial outwash sequence that is immediately below the Olympia beds in the south-central lowland may be correlative with the Possession Drift of the northern lowland. Similarly, many exposures of the second nonglacial interval exposed at or near sea level may correlate with the northern Whidbey Formation or with older, reversely magnetized nonglacial units. The use of the name ‘Kitsap Formation’ for the second nonglacial sediments and thick fine-grained deposits encountered in the study area is misleading and should be discontinued.

INTRODUCTION This paper presents stratigraphic and chronologic data from dating techniques for Pleistocene sediments older than about west-central Pierce County in the south-central Puget Lowland 45,000 yr B.P. (Fig. 1). The study focused on late Pleistocene stratigraphic Willis (1898) and Bretz (1913) established the initial strati- units that are exposed in outcrop and encountered in boreholes graphic framework for Quaternary sediments in the Puget Low- in the Tacoma area. We examined boring logs and subsurface land. They identified two glacial units separated by a single non- samples from more than 120 boreholes, performed reconnais- glacial unit. In the southern lowland, the stratigraphic sequence sance-scale geologic mapping, and made seven detailed mea- was later modified by Crandell and others (1958), based on measured sections at key outcrops. Sixteen new radiocarbon dates sured sections near the town of Sumner, about 10 mi southeast of are presented here from both outcrop and subsurface locations. the Tacoma area. The revised stratigraphic sequence consisted The new radiocarbon dates confirm the presence of discon- of four glacial units and three intervening nonglacial units: tinuous but widespread occurrences of nonglacial sediments Vashon Drift—unnamed nonglacial—Salmon Springs that are correlative by age and character with the sediments de- Drift—Puyallup Formation—Stuck Drift—Alderton posited during the Olympia climatic interval. The presence of Formation—Orting Drift the Olympia beds also means that the underlying glacial out- Crandell and others (1958) believed that the erosional con- wash sequence, previously assigned to the Vashon Drift by other tact between the Vashon Drift and the Salmon Springs Drift in workers, is actually an older glacial drift. their study area was representative of a nonglacial period, but did not apply a name to it. Stratigraphic Nomenclature Sceva (1957) first applied the name “Kitsap Clay Member of The late Pleistocene (300,000–10,000 yr B.P.) stratigraphic se- the Orting Gravel” to predominantly fine-grained sediments ex- quence in the Puget Lowland records repeated advances of the posed beneath the Vashon Drift in Kitsap County northwest of Cordilleran ice sheet into the area (Fig. 1). Numerous workers the study area. He interpreted these deposits to be glacial in ori- have studied the glacial and nonglacial stratigraphy and at- gin. Working on the Kitsap Peninsula, Molenaar (Garling and tempted to make regional, basin-wide correlations of strati- others, 1965) redefined the Kitsap Formation as a nonglacial graphic units (Table 1). These attempts have been hampered by unit that separates the Vashon Drift from the Salmon Springs limited outcrops in much of the lowland, the complexity of the Drift and correlated it with the Olympia climatic interval. The stratigraphic sequence, and until recently, the lack of reliable study also applied the name “Colvos Sand” to a distinct sand se-

1 2 REPORT OF INVESTIGATIONS 33 quence at the base of the Vashon Drift. Walters and Kimmel fied at this exposure. The Lawton Clay Member was defined as (1968) adopted this nomenclature while mapping in the Tacoma glaciolacustrine clay and silt deposited in an ice-dammed lake area and used the following stratigraphic sequence: that formed as the Vashon glacier entered the Seattle area. Vashon Drift (with a distinct basal member called the In the mid 1960s, based upon the work of numerous re- Colvos Sand)—Kitsap Formation—Salmon Springs searchers, the following sequence was presumed to be valid Drift—Puyallup Formation—Stuck Drift—Alderton across the entire Puget Lowland: Formation—Orting Drift Fraser Glaciation (composed of the Sumas Stade, In the northern lowland, Armstrong and others (1965) de- Everson Interstade, Vashon Stade and Evans Creek fined the “Olympia Interglaciation” as the climatic episode im- Stade)—Olympia Interglaciation—Salmon Springs mediately preceding the last major glaciation and lying immedi- Glaciation—Puyallup Interglaciation—Stuck Glaci- ately beneath the Vashon Drift. In British Columbia, the name ation—Alderton Interglaciation—Orting Glaciation “Quadra” was already in use to describe these deposits (Arm- The Evans Creek Stade of the Fraser Glaciation represents a strong and Brown, 1954). The Vashon Drift in the northern low- period of alpine glaciation while the lowland remained free of land was assigned to one of four stades of the Fraser Glaciation. ice. The Vashon Stade represents the period when the Cordille- Armstrong and others (1965) also compiled radiocarbon dates ran ice sheet invaded the lowland and advanced south of the Ta- of between 15,000 and 35,000 yr B.P. for the Olympia Inter- coma area. Deposits associated with the Sumas Stade and Ever- glaciation from throughout the Puget Lowland and proposed the son Interstade have been identified only in the northern lowland. type section at Fort Lawton in Seattle. Mullineaux and others Further work by Easterbrook and others (1967) and Easter- (1965) also identified the nonglacial sediments exposed imme- brook (1968, 1969) on Whidbey Island resulted in the naming of diately beneath the Vashon Drift at Fort Lawton as correlative additional units within the following sequence: with the Olympia sediments of Armstrong and others (1965) to Vashon Drift—Quadra Formation (Olympia Interglaci- the north and with the Kitsap Formation of Molenaar (Garling ation)—Possession Drift—Whidbey Formation—Dou- and others, 1965) to the south. Two basal members of the Vashon ble Bluff Drift Drift, the Esperance Sand and the Lawton Clay, were also identi- While mapping in Kitsap County to the northwest of Tacoma, Deeter (1979) 124° 123° 122°W determined that the sediments previously 49°N defined as the Kitsap Formation at their type section actually consisted of three WHATCOM stratigraphic units (Easterbrook’s Whid- Vancouver Bellingham bey Formation, Possession Drift, and Island SAN Olympia nonglacial sediments). He pro-

JUAN posed to continue using the term “Kitsap Formation” but with the strict definition Strait of Juan de Fuca Victoria SKAGIT that it only includes sediments deposited Whidbey ? during the Olympia climatic interval of CANADA Island Armstrong and others (1965). USA ISLAND Additional radiocarbon dates from CLALLAM the sediments deposited during the Olym- of Vashon SNOHOMISH limits 48° pia climatic interval indicate that they ac- ? ice Everett maximum cumulated between about 15,000 and Skykomish OLYMPIC River 60,000 yr B.P. (Deeter, 1979; Hansen and

Snoqualmie R. Easterbrook, 1974; Clague, 1981; Troost, OLYMPICPENINSULA MOUNTAINS SOUND 1999). These dates closely approximate Canal Seattle JEFFERSON KITSAP the limiting ages for oxygen isotope stage 3 and immediately predate stage 2 (the PUGET Hood Fraser Glaciation) (Winograd and others, KING PACIFIC 1997). Most current researchers do not el- Green evate oxygen isotope stage 3 to full inter- OCEAN GRAYS MASON River HARBOR PUGET LOWLAND glaciation status (Winograd and others, Tacoma White R. 1997; Shackleton, 1969; Clark, 1992). Hansen and Easterbrook (1974) have also Chehalis STUDY PuyallupPIERCE 47° River Olympia CASCADE RANGE identified glacial sediments in portions of AREA R. THURSTON the northern lowland that they believed to have been deposited during the same time Mount Rainier interval. For these and other reasons, the LEWIS term “Olympia Interglaciation” has not PACIFIC River been used consistently in the literature Cowlitz since it was proposed in 1965. Pessl and others (1989) used the term “Olympia 0 20 WAHKIAKUM Mount beds” to describe deposits of the Olympia COWLITZ Mount miles St. Helens Adams climatic interval, without implying a cli- ORE. matic rank. Their convention is also used Figure 1. Puget Lowland and study area. in this paper. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 3 (ka) Age Easterbrook (1986), Blunt and others (1987), Easterbrook (1994), Troost (1999) Lawton Clay Puget Lowland Puget Lowland Easterbrook (1968) Central and northern Easterbrook and others (1967), Possession DriftWhidbey FormationDouble Bluff Possession Drift Drift Whidbey Formation Double 60–80 Bluff Drift ~100 100–250 (1968) Steilacoom Gravel Steilacoom Gravel Walters and Kimmel (ka) C age 15–25 14 11–13.5 Puget Lowland Tacoma area Central and northern Vashon tillEsperance SandLawton Clay Colvos Vashon Sand till Esperance Sand Vashon till Armstrong and others (1965), Mullineaux and others (1965) Sumas StadeEverson Interstade (glaciomarine) 9–11 Vashon Stade 13.5–25 Vashon Drift Vashon Drift Vashon Drift Evans Creek Stade (alpine) Olympia Interglaciation 15–35 Kitsap Formation Quadra Formation Olympia beds 15–60 (1958) Southern Puget Lowland Crandell and others (Vashon till) Salmon Springs Drift SalmonPuyallup Springs Formation GlaciationStuck Puyallup Drift InterglaciationAlderton FormationOrting Alderton Drift Interglaciation Salmon Springs Drift Stuck Glaciation Puyallup Formation Orting Glaciation Alderton Formation Stuck Drift Orting Drift Salmon Springs Glaciation 800 Puyallup Interglaciation >1000 Alderton Interglaciation >1600 Stuck Glaciation Orting Glaciation ~1600 >1600 Unnamed erosional/ nonglacial interval Bretz (1913) Willis (1898), Puget Lowland Vashon glaciation Vashon Drift Admiralty glaciation Puyallup Interglaciation 10 Fraser Glaciation

300 800

(ka) Puget Lowland stratigraphic nomenclature. *, not to scale 1800 Age*

LATE MID EARLY

CENE

HOLO- PLEISTOCENE Table 1. 4 REPORT OF INVESTIGATIONS 33

In the past 20 years, the development of new age-dating Recent Investigations in the Study Area techniques, including fission track, laser-argon, thermolumines- Recent investigators in the Tacoma area have postulated that cence, paleomagnetism, and amino-acid analysis, has allowed sediments previously assigned to the base of the Vashon Drift early-stage Olympia beds and older units to be dated. Easter- actually represent an additional set of nonglacial and glacial brook and others (1981) determined that the fine-grained sedi- units. The age, character, and extent of these units were not well ments in the middle of the Salmon Springs Drift were about one defined. During a large subsurface study in the Tacoma area, million years old. Subsequent work has shown the Double Bluff Brown and Caldwell, Inc., and others (1985) identified a discon- Drift to be about 150,000 to 250,000 years old and the Whidbey tinuous layer in the subsurface that divided the inferred Vashon Formation to be about 100,000 years old (Easterbrook, 1986; Drift in two. This layer, designated as layer A1 by Brown and Blunt and others, 1987; Easterbrook, 1994). Based upon these Caldwell, consisted of clay and sand with abundant organic mat- studies, the Pleistocene sequence in the Puget Lowland is com- ter. Based upon a single radiocarbon date collected from a bore- posed of the following units: hole on Fort Lewis, Noble (1990) suggested that layer A1 sedi- Vashon Drift (Fraser Drift with multiple stades in the ments are correlative with sediments deposited during the north)—Olympia beds—Possession Drift—Whidbey Olympia climatic interval of the northern lowland. He proposed Formation—Double Bluff Drift—Salmon Springs the name “Discovery nonglacial unit” for these deposits after the Drift—Puyallup Formation—Stuck Drift—Alderton most southerly known surface exposure of confirmed Olympia Formation – Orting Drift beds at Discovery Park in the Seattle area (Mullineaux and oth- The Double Bluff Drift marks the base of late Pleistocene ers, 1965). He also proposed that the underlying glacial drift be sediments in the lowland and is separated from the early Pleisto- named the “Narrows glacial unit” and tentatively correlated it to cene fine-grained interbeds in the middle of the Salmon Springs the Possession Drift of the northern lowland. Another large Drift by a data gap of at least 700,000 years. study conducted for the South King County Groundwater Advi- This complex history has resulted in the use of two sets of sory Committee and others (1991) immediately north of the Ta- late Pleistocene stratigraphic nomenclatures in the Puget Low- coma area also identified inferred Olympia beds in the sub- land, one based on the younger deposits to the north of Seattle surface and an additional glacial drift immediately beneath it. In and one based on generally older deposits to the south (Table 1). our earlier work, we first identified outcrops of the Olympia In the south-central Puget Lowland, only two glacial sequences beds in the Tacoma area (Borden and Troost, 1995). and a single nonglacial sequence have traditionally been recognized above sea level. The name “Kitsap Formation” has contin- FIELD AND LABORATORY PROCEDURES ued to be loosely applied to nonglacial deposits separating the overlying Vashon Drift from the inferred Salmon Springs Drift. Numerous environmental and geotechnical investigations in The name Salmon Springs Drift has been loosely applied to the west-central Pierce County have provided more than 120 deep iron-oxide-stained drift occurring at around sea level and (or) borehole logs in a nine-square-mile area for use in the present the next glacial drift below the Vashon. study. Between 1986 and 1996, core samples from approximately 60 of these boreholes were collected and archived during

122°37.5¢ 122°30¢

PUGET 5 BA-01 SOUND Gravelly McCHORD Lake AIR FORCE

CW-32 BASE FORT LEWIS CA-01 E CW-30 Solo Point C CW-31 MILITARY RESERVATION DA-15 measured CW-15 section DA-26 Well 5001 CW-14 FZ-01 90-PM-1 Poe & DA-13 CW-06 McGuire DA-24 DZ-10 CW-18 D T-09 DA-17 DA-11 DZ-01 EH-4 LT-09 T-11 DZ-06 American Lake A T-12 DA-12e DZ-09 T-02 CW-33 TZ-02 DA-07 T-10 W3 W1 GC TZ-01 DA-25 47°7.5¢ T-01 DA-20 W4 W2 CW-34 LC-60 LC-61 DA-16 DA-12 DA-02 LF4-MW12B O'Neil & DA-08 IH-01 88-5-SS LC-71 LC-38 A¢ Martin DA-18 DA-04 DA-01 LF4-MW16B LZ-04 LC-72 LC-40 LC-66 0 2000 4000 ft LF4-MW4 LC-44 88-1-SS LF4-MW3B LC-73 LF4-MW6SB LC-67 LC-70 LC-69 scale (B) RD-1 LC-47 LC-22 LF4-MW1B EXPLANATION RD-2 LC-41 LC-65 LC-68 LC-55 Boring used in 5 Well 4/6 LC-35 Well 8 LC-72 cross sections or Comp D¢ LC-19 LC-21 LC-26 contour maps FORT LEWIS LC-50 LC-64 C¢ E(B)¢¢ Cross section MILITARY RESERVATION AA¢ location

Figure 2. Borehole and cross section location map. See Appendix A for additional borehole information. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 5 field investigations conducted by Shannon & Wilson, Inc., and sources (Fig. 3; see Table 3 for a summary of radiocarbon data). Foster Wheeler Environmental Corporation. Samples were typi- The radiocarbon analyses were performed by Beta Analytic, cally collected on a 5 or 10 ft interval. We originally logged Inc., Teledyne Isotopes, and the Illinois State Geological Sur- many of these boreholes. These boreholes were used to con- vey. Paleomagnetic measurements were also made at two of the struct detailed cross sections and paleotopographic maps. Infor- measured sections as part of the Pacific Northwest Urban Corri- mation on boreholes used in the study is summarized in Appen- dor Mapping Project. The paleomagnetic samples were col- dix A, and borehole locations are shown on Figure 2. lected and analyzed by Jonathan T. Hagstrum of the U.S. Geo- We re-examined borehole samples under a binocular micro- logical Survey in Menlo Park, California (written commun., scope. Mineralogic and lithologic point counts were made on 1997; Troost and others, 1997). A single sample was also col- sand grains from many samples, as well as descriptions of sand lected from one of the measured sections and analyzed by fis- grain iron staining, roundness, angularity, and sorting. We made sion-track dating (Richard J. Stewart, Univ. of Wash., written borehole correlations on the basis of texture, color, mineralogy, commun., 1999). organic matter content, oxidation intensity, and stratigraphic position. Being able to directly compare samples from different GLACIAL AND NONGLACIAL DEPOSITION boreholes, rather than comparing borehole logs alone, allowed IN THE PUGET LOWLAND us to make correlations with greater certainty than in many previous studies. To aid in the microscope investigation, samples The study area is underlain by a complex, 1300 to 2000 ft thick from selected Puget Lowland rivers were also collected and ex- sequence of alternating glacial and nonglacial Quaternary sedi- amined. ments (Jones, 1996). Previous investigations have suggested at We conducted reconnaissance-scale outcrop surveys and least six advances of the Cordilleran ice sheet into the Puget mapping at selected sites surrounding the subsurface study area. Lowland during the Pleistocene (Easterbrook, 1994). Glacial Seven detailed measured sections were made at key outcrops in sediments represent periods when the lowland was invaded by the west-central Pierce County area. We obtained radiocarbon the Cordilleran ice sheet from the north. Nonglacial sediments dates both from outcrops and boreholes during this study and we represent periods when the lowland was free of ice, although al- report three additional dates here from other unpublished pine glaciers may, at times, have occupied many of the surrounding mountain ranges. During alpine glacial periods such as the Evans Creek Stade of the Fraser Glaciation, glacial outwash probably reached the study area from the 122°30¢ Mount Rainier area, but these sediments are not differentiated from true nonglacial sediments in this study.

Maury Island This ideal succession of glacial and nonglacial sed- Colvos Vashon SOUND iments is complicated by the repeated deep erosional Passage Island events that are likely associated with each glacial pe- PUGET riod (Bretz, 1913; Crandell and others, 1965; Borden 16 POINT and Troost, 1994; Booth, 1994) and by the poor sedi- DEFIANCE mentary record left by some nonglacial intervals. Boathouse Nonglacial Deposits Commencement Lowland sedimentation during nonglacial periods is Bay Hylebos Waterway Woodworth dominated by relatively low-energy fluvial systems. Narrows Manke Lacustrine and marine deposition may be significant TACOMA Puyallup Foran The towards the center of the lowland, and volcaniclastic 47°15¢ deposits such as lahars and tephras may be common

River 5 nearer volcanoes on the margin of the lowland. Sedi- ment transport by nonglacial rivers is generally from Sunset Route 7 Beach the mountains toward the center of the lowland, subperpendicular to the north-south axis of the Puget trough. Large areas of the lowland may be subjected to erosion or nondeposition and soil development during SOUND 7 nonglacial periods. In many places, nonglacial intervals are only marked by paleosols representing a 5 PUGET weathering profile or a thin accretionary soil devel- 03mioped on top of a glacial sequence. scale The present-day Puget Lowland provides a useful Solo analog for previous nonglacial periods. As shown on Point EXPLANATION American McCHORD Figure 4, most of the present day lowland is dominated AFB Lake DA-12e MW-12 DA-2 Measured section by areas of nondeposition, soil formation, or erosion. with14 C data Significant sediment accumulation is occurring in 4/6 Comp Boring with14 C data widely separated river valleys, lake basins, and the Puget Sound. If the present-day lowland were invaded FORT LEWIS Limits of subsurface MILITARY RESERVATION investigation by glacial ice or by outwash deposits related to a Cordilleran ice sheet, a complicated and discontinuous Figure 3. Locations of radiocarbon samples. See Table 3 for radiocarbon data record of nonglacial deposition would be buried by and Appendix B for borehole logs with radiocarbon data. glacial deposits and preserved in the stratigraphic re- 6 REPORT OF INVESTIGATIONS 33 cord. Thick sedimentary sequences would pinch out abruptly deposits of different nonglacial intervals generally cannot be against valley walls. Sediments deposited in river valleys and differentiated on the basis of sedimentology and sediment basins could be several hundred feet lower than time-equivalent source area alone, because similar geologic conditions exist dur- sediments or organic-rich paleosols that formed on nearby up- ing each nonglacial interval. A study of stratigraphic relation- lands. The thickness and lateral continuity of nonglacial sedi- ships in conjunction with absolute dating at key locations is re- ments representing a given nonglacial interval is probably de- quired to reliably correlate units. pendent upon several variables, including the duration of the nonglacial interval, subsidence rates in the lowland during the Glacial Deposits nonglacial interval relative to global sea level, the elevation and Glacial sedimentary units are dominated by ice-contact facies surface topography of fill left in the basin by the preceding gla- such as till, glaciolacustrine facies, and high-energy glacioflu- cial incursion, and the depth of erosion of the following glacial vial facies. The dominant sediment transport direction is from incursion. north to south, subparallel to the axis of the Puget trough. Gla- Nonglacial sediments within the study area are largely de- ciolacustrine sediments commonly mark the base of each glacial rived from Mount Rainier, the 14,400 ft volcanic peak located sequence. These sediments were deposited in proglacial lakes about 40 mi to the east-southeast (Fig. 5) (Crandell and others, that formed when the southward advancing ice disrupted the 1958; Walters and Kimmel, 1968; Mullineaux, 1970). Mount interglacial (northward) drainage network in the lowland, and Rainier sediments are characterized by an abundance of they represent a transition from nonglacial to glacial sedimenta- andesitic lithic fragments, a paucity of quartz, and a lavender or tion. In an ideal section, glacial sediments are represented by the reddish gray color (typically 5YR 3/1 on a Munsell color chart). following sequence, from bottom to top: (1) fine-grained, gla- The late Pleistocene nonglacial sediments exposed in the Ta- ciolacustrine sediments, (2) coarsening-upward advance out- coma area are very similar to sediments being transported by the wash, (3) till and poorly sorted ice-contact deposits, and (4) fin- modern White and Puyallup Rivers (Fig. 5). Unless they contain ing-upward recessional outwash locally interbedded with dead- distinct marker beds such as tephras with unique mineralogies, ice deposits. North of the marine limit, this sequence could be capped by glaciomarine drift (near Seattle for the Vashon Stade). 123° 122°

123° 122° Nooksack R. Qnd

Bellingham Mount 48° Qm Baker

Skagit R.

PUGET SOUND Ql CANADA approximate USA Seattle Qnd limits of Quaternary basin fill Qnd Stillaguamish R.

Snow Cr. 48°

Little Quilcene R. PUGET Qm Quilcene R. Skykomish R. Qm Dosewallips R.

Tacoma Qa Duckabush R. Seattle Hama Hama R. SOUND Snoqualmie R.

Qnd approximate 47° limits of Cedar R. Quaternary basin fill Skokomish R. Green R.

Tacoma 0 10 mi White R. EXPLANATION scale 0 10 mi Qm Qnd Areas of erosion or nondeposition Marine deposition Carbon R. (may include small laterally and scale 47° Puyallup R. Qa Alluvial deposition temporally discontinous alluvial and lacustrine environments) EXPLANATION Mount Ql Lacustrine deposition River sediment Nisqually R. sample location Rainier

Figure 4. Modern Puget Lowland depositional environments. Source: Huntting and others (1961). Figure 5. Location map of Puget Lowland river sediment samples. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 7

Glacial sediments within the study area are predominantly sediments such as tephras and lahars are also more typical of derived from the central Cascade Range, with exotic lithologies nonglacial units. The lack of volcanogenic sediments in glacial from the North Cascades and Canada. Glacial outwash sand sequences is probably due to the relatively short duration of most closely resembles the sediments being carried into the low- most glacial periods in the lowland, the rapid rate of sediment land by the modern-day Snoqualmie and Skykomish Rivers accumulation during glacial periods, and the lack of low-energy (Fig. 5). These sediments are characterized by an abundance of depositional environments during glacial periods where tephras quartz, mica, granodiorite, and green lithic fragments, and are can accumulate and be preserved. olive-gray in color (typically 5Y 3/2 on a Munsell color chart). During glacial periods, the apparent source of sediments is Deposits associated with the various glacial events may look re- from the north. In the Tacoma area, nonglacial sediments are markably similar, and at outcrop scale they can commonly be predominantly derived from Mount Rainier to the southeast. differentiated only by their stratigraphic position or degree of However, glacial sediments are dominated by lithologies with weathering. sources from the central Cascades more than 30 miles north of Mount Rainier. Similarly, nonglacial sediments that are exposed Differentiating Glacial and Nonglacial Sediments along Hood Canal on the western margin of the lowland are predominantly composed of lithologies from the Olympic Moun- Glacial and nonglacial sediments can often be differentiated on tains (Borden, 1998), but glacial sediments contain a large com- the basis of sedimentary facies and sediment source areas. ponent derived from the North Cascades. This relationship is Till is the most distinctive glacial facies in most drift se- probably valid for glacial and nonglacial sediments throughout quences. Its lack of sorting and bedding, matrix support of the the lowland, but it may be locally complicated by the reworking clasts, and dense nature make it easy to distinguish from most of older glacial sediments during interglacial periods and by the types of nonglacial sediments except for lahars. Till can gener- incorporation of locally derived rock and sediment into some ally be differentiated from lahars on the basis of sediment source glacial deposits. area and by a lack of organic material. Unlike till associated with To aid in source area identification during this study, we col- a Cordilleran ice sheet, lahars in the study area are typically lected sediment samples from most of the major rivers that drain composed of sediments from Mount Rainier and contain pockets into the Puget Lowland (Fig. 5). Samples of fine and coarse sand of organic matter. Glacial outwash sequences tend to be thick, were examined under a binocular microscope and gravel homogeneous, and relatively coarse when compared to nongla- lithologies were determined. Selected lithologic characteristics cial fluvial sequences, and tend to have a different sediment that are easily identifiable in outcrop and in borehole samples source area. are listed for each river sample in Table 2. Sand from rivers The presence of peat or organic-rich sediments is usually in- draining Quaternary volcanic peaks such as Mount Rainier or dicative of nonglacial depositional environments. Volcanogenic

Table 2. Sediment characteristics of selected Puget Lowland rivers. (1), Munsell color chart designation listed in parentheses; (2), source lithologies listed in order of decreasing exposure surface area in drainage basin % Red River Sand color (1) % Quartz andesite % Mica Source lithologies (2) Nisqually dark brown (7.5 YR 3/2) 60 5 trace andesite, Mount Rainier volcanics Puyallup black (5 YR 2.5/1) 40 10 trace andesite, Mount Rainier volcanics Carbon very dark grey to reddish black 50 10 trace–1% andesite, Mount Rainier volcanics, granites (5 YR 3/1 to 10 R 2.5/1) White dark brown to reddish black 40 10 0 andesite, Mount Rainier volcanics (7.5 YR 3/2 to 10 R 2.5/1) Green very dark greyish brown (2.5 Y 3/2) 50 trace trace andesite Cedar very dark greyish brown (2.5 Y 3/2) 45 trace trace andesite, granites Snoqualmie very dark greyish brown to black 65 0 trace–2% granites, greywacke, argillite, andesite (2.5 Y 3/2 to 5 Y 2.5/2) Skykomish olive grey to dark olive grey 65 0 2–3% granites, greywacke, argillite, andesite (5 Y 3/2 to 5 Y 4/2) Stillaguamish very dark grey to dark olive grey 60 trace trace–1% sandstones, argillite, metasediments, granites (5 Y 3/1 to 5 Y 3/2) Skagit very dark greyish brown (10 YR 3/2) 70 2 1–2% metasediments, argillite, gneiss, granites, Mount Baker volcanics Nooksack very dark grey (10 YR 3/1) 45 5 trace–1% sandstones, metasediments, Mount Baker volcanics, granodiorite, dunite Snow Creek dark brown (10 YR 3/3) 50 0 0 sandstones, argillite Little Quilcene very dark greyish brown (10 YR 3/2) 35 0 0 basalt, sandstones, argillite Quilcene black (10 YR 2/1) 15 0 0 basalt Dosewallips black (5 Y 2.5/1) 20 0 0 basalt, greywacke, argillite Duckabush black (5 Y 2.5/1) 15 0 0 basalt, greywacke, argillite Hama Hama dark brown to black 10 0 0 basalt, greywacke, argillite (7.5 YR 3.2 to 5 Y 2.5/2) Skokomish very dark greyish brown (2.5 Y 3/2) 10 0 0 basalt, greywacke, argillite 8 REPORT OF INVESTIGATIONS 33

Table 3. Summary of radiocarbon data. The radiocarbon dates have not been converted to calendar years and show a laboratory error of one stan- dard deviation. Sample locations are shown in Figure 3. The Illinois State Geological Survey (ISGS) served as an independent quality assurance laboratory for two samples dated by Beta Analytic, Inc. (Beta). ft MSL, feet above mean sea level; B.P., before present; I, Teledyne Isotopes. *, accel- erator mass spectrometry radiocarbon dating corrected for 13C/12C ratio, believed to be reworked charcoal from an older stratigraphic unit. All but three samples were collected during this study: †, Timothy J. Walsh, Wash. Div. of Geology and Earth Resources, written commun., 1995; §, date obtained by Shannon & Wilson, Inc., in 1988; #, date obtained by Shannon & Wilson, Inc., in 1989 Approx. Conventional elevation, Laboratory 14C age, Site name Location ft MSL Sample type sample no. yr B.P. Stratigraphic position Woodworth quarry SW¼SW¼ sec. 25, 193 charcoal Beta-95340 >53,480 * Vashon advance outwash T21N R3E Borehole DA-12e SW¼SW¼ sec. 14, 180 wood Beta-79885 13,510 ±80 Vashon glaciolacustrine sediments T19N R2E Sunset Beach SW¼NW¼ sec. 16, 140 flattened wood ISGS-3343 12,960 ±180 Vashon glaciolacustrine sediments T20N R2E Sunset Beach SW¼NW¼ sec. 16, 140 flattened wood Beta-89876 13,620 ±80 Vashon glaciolacustrine sediments T20N R2E Borehole MW-12b † NE¼SW¼ sec. 19, 176 peaty silt Beta-52222 13,630 ±90 Vashon glaciolacustrine sediments T19N R2E Route 7 SW¼SE¼ sec. 9, 210 organic sediment Beta-89256 17,110 ±290 Olympia beds T20N R3E Borehole 4/6 § SW¼NE¼ sec. 28, 210 wood I-15,437 25,100 ±600 Olympia beds T19N R2E Woodworth quarry SW¼SW¼ sec. 25, 164 organic sediment ISGS-3301 27,530 ±390 Olympia beds T21N R3E Woodworth quarry SW¼SW¼ sec. 25, 164 organic sediment Beta-80937 32,040 ±690 Olympia beds T21N R3E Manke quarry NE¼SE¼ sec. 36, 137 paleosol Beta-87981 36,650 ±720 Olympia beds T21N R3E Solo Point SW¼NW¼ sec. 13, 80 peat Beta-120064 41,380 ±1940 Olympia beds T19N R1E Woodworth quarry SW¼SW¼ sec. 25, 240 organic sediment, Beta-86842 >41,710 Olympia beds T21N R3E paleosol Foran quarry NW¼SW¼ sec. 31, 130 peat Beta-89875 >46,450 Olympia beds T21N R4E Borehole DA-2 # NW¼NW¼ sec. 24, 204 wood I-15,705 >40,000 pre-Olympia drift T19N R2E Borehole DA-12e SW¼SW¼ sec. 14, 132 wood Beta-81801 >41,300 pre-Olympia drift T19N R2E Boathouse NE¼SW¼ sec. 14, 27 peat Beta-80938 >46,750 pre-Vashon nonglacial deposits T21N R2E

Mount Baker tend to have a reddish hue and contain distinctive However, recent field studies and radiocarbon dates show that red andesite grains. Sand from rivers elsewhere in the Cascades throughout the area, an upper nonglacial sequence exposed be- generally has a greenish or yellowish hue. The presence of mus- tween 130 and 240 ft above mean sea level (ft MSL) separates covite mica and a relatively high quartz content is diagnostic of Vashon Drift from an underlying oxidized outwash sequence. sand from rivers draining granitic source areas. Rivers draining The radiocarbon dates obtained from this nonglacial sequence the Olympic Peninsula have sands that are dominated by black vary from 27,530 yr B.P. to >46,450 yr B.P. These ages are at or very dark gray lithic fragments and contain very little quartz. least in part correlative with sediments deposited during the Gravel lithologies tend to reflect the bedrock exposures within Olympia climatic interval. This stratigraphic sequence is later- the drainage basins with a strong bias towards more resistant ally continuous for more than 2 mi along the southwest-facing lithologies. bluff. A lower nonglacial sequence is locally exposed at the foot of the bluff. RESULTS The westernmost measured section is from an exposure at Woodworth quarry (Fig. 6). Here, the Olympia beds are about 50 Radiocarbon dating information is summarized in Table 3. De- ft thick and consist of two distinct facies: a paleosol developed tailed descriptions of the geologic setting at each sample site are on a lahar and an underlying andesitic fluvial sand. The lahar provided below, along with measured sections and cross sec- and sand are composed mostly of pumice, andesite, and tions. tuffaceous clasts. Locally a thin peat and an ash layer are present above the lahar. The Olympia beds are not present across the en- Hylebos Waterway Measured Sections tire quarry exposure. Where absent, a sharp contact occurs be- Radiocarbon dates were obtained from three widely separated tween an unoxidized outwash sequence above (Vashon out- exposures on a 400 ft high bluff on the north side of the Hylebos wash) and an oxidized outwash sequence below. A thin paleosol Waterway (Fig. 3). These outcrops were previously mapped as is commonly developed at the contact on top of the oxidized out- Vashon Drift over Salmon Springs Drift (Waldron, 1961). wash. Organic debris collected from the paleosol at two different locations in the quarry has radiocarbon dates of 27,530 ±390 LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 9 yr B.P. (ISGS-3301), 32,040 ±690 yr B.P. (Beta-80937) and andesitic and tuffaceous sand with two peat beds near the top of >41,710 yr B.P. (Beta-86842). A lower nonglacial sequence is the sequence. The lowermost peat bed has a radiocarbon date of exposed immediately above sea level downhill from the quarry. >46,450 yr B.P. (Beta-89875). Despite the infinite radiocarbon It is composed of andesitic sand and silt with at least four tephra date, these sediments are believed to correlate with the dated interbeds. These deposits are reversely magnetized and so are Olympia beds at Manke quarry because they crop out at a com- likely to be older than 780,000 years B.P. (Troost and others, parable elevation and are exposed between the same two drift 1997). This is supported a preliminary fission-track date of sequences. The Vashon Drift is in erosional contact with the un- 1,100,000 ±150,000 yr B.P. from this lower nonglacial sequence derlying sediments in Foran quarry. A Vashon erosional channel (Richard J. Stewart, Univ. of Wash., written commun., 1999). at least 150 ft deep and filled with coarse gravel cuts through the The Manke quarry section (Fig. 7) is exposed on the same nonglacial sediments and is deeply incised into the underlying bluff about one mile southeast of Woodworth quarry. The Olym- oxidized glacial drift. pia beds are intermittently exposed on the bluff between the two quarries. The same stratigraphic sequence is exposed at both Route 7 Measured Section quarries except that the basal nonglacial sediments are not visi- The Route 7 section (Fig. 9) is exposed on either side of the ble at Manke quarry. The Olympia beds at Manke quarry are 25 highway about 2300 ft south of the intersection with Interstate 5 ft thick and consist of interbedded andesitic sand, sandy silt, and (Fig. 3). The exposure is approximately 4 mi southwest of the tephra. Two peat beds are exposed towards the bottom of the Hylebos Waterway sections. This exposure was originally nonglacial sequence. The uppermost peat bed has a radiocarbon mapped as Vashon Drift by Smith (1977). Our measurements in- date of 36,650 ±720 yr (Beta-87981). The nonglacial sedi- B.P. dicate that a 92 ft thick Vashon Drift sequence is underlain by a ments separate Vashon Drift above from an underlying highly 46 ft thick Olympia bed sequence at this exposure. An older, oxidized glacial drift. highly oxidized glacial outwash is exposed beneath the non- The Foran quarry section (Fig. 8) is exposed about a quarter glacial deposit. The Olympia beds consist of a massive basal of a mile southeast of the Manke quarry. Nonglacial sediments mudflow with overlying fluvial gravel. The fluvial gravel con- are intermittently exposed on the bluff between the two quarries. tains lithologies characteristic of both Mount Rainier and the At Foran quarry, the nonglacial sediments are about 16 ft thick North Cascades. The gravel is capped by a 2 ft thick gray lami- and separate Vashon Drift above from an underlying highly oxi- nated silt at an elevation of 210 ft . Organic-matter-rich sed- dized glacial drift. The nonglacial sediments are composed of MSL iments at the base of the silt yield a radiocarbon age of 17,110 ±290 yr B.P. (Beta-89256). UPLAND SURFACE Vashon Drift Till overlying cross-bedded to laminated to massive sand with EXPLANATION 300 northern Cascades lithologies cl clay till silt si silt fs fine sand sand peat ms medium sand cs coarse sand sandy gravel diamicton (lahar) gr gravel tephra

14C: >53,480 yrB.P. (AMS, Beta-95340); 200 COVERED ) date on detrital charcoal 200 Vashon advance outwash

L S Cross-bedded to laminated to massive

tM Olympia beds sand and gravel with northern Cascades

(f lithologies

on Predominantly volcanic lithologies, dated i peat and paleosol overlie tephra, lahar, and diatomaceous layer; mixed lithology gravel Olympia beds Elevat at top Predominantly volcanic lithologies, 14C: 32,040 ±690 yrB.P. (Beta-80937); pumaceous sand (lahar runout), and silt; 27,530 ±390 yrB.P. (ISGS-3301) mixed lithology gravel at top 14C: 36,650 ±72 yrB.P. (Beta-87981) 14C: >41,710 yrB.P. (Beta-86842); date on 100 paleosol in interior part of quarry 100 Sub-Olympia drift Sub-Olympia drift Highly oxidized gravel with northern

Highly oxidized gravel with northern Elevation (ft MSL) Cascades lithologies Cascades lithologies, clayey and intensely oxidized at top

Pre-Olympia nonglacial deposits Sand with predominantly volcanic litholo- COVERED gies, reversely magnetized, with four COVERED tephra layers, zircon fission-track dated at 0 1.1 ±0.15 Ma (Richard J. Stewart, Univ. of 0 Wash., written commun., 1999) cl si fsms cs gr cl si fs ms cs gr

Figure 6. Woodworth quarry composite measured section, Poverty Figure 7. Manke quarry measured section, Poverty Bay 7.5-minute Bay 7.5-minute quadrangle, lat 47.2729 N, long 122.3728 W. quadrangle, lat 47.2642 N, long 122.3532 W. 10 REPORT OF INVESTIGATIONS 33

The laminated silt also contains a single, 0.5 in. thick tephra eruptions that spanned several thousand years (Beget and oth- layer several inches above the radiocarbon-dated material. The ers, 1997). age of this tephra is constrained to a relatively brief period be- The tephra identified at the Route 7 exposure in Tacoma may tween the underlying date of 17,110 yr B.P. and the inception of correlate with a tephra identified about 12 mi south in the Ohop Vashon glaciation in the Tacoma area several thousand years Valley (Beget and others, 1997), which is also contained within later. No tephras have yet been identified within this time frame lacustrine sediments at the base of the Vashon Drift. The Ohop that originate from Mount Rainier about 40 mi to the east-south- Valley tephra has been positively correlated with Mount St. Hel- east (Pringle and others, 1994). However, the tephra could be ens set S based upon several geochemical and mineralogical cri- derived from Mount St. Helens about 74 mi to the south. The ash teria, although because of its stratigraphic position it is pre- contains cummingtonite (Patrick T. Pringle, Wash. Div. of Geol- sumed to be older than 14,500 years B.P. (Beget and others, ogy and Earth Resources, oral commun., 1996), which is unique 1997). to Mount St. Helens tephras and is particularly abundant in tephra set S (Mullineaux, 1986). Radiocarbon-dated organic Tacoma Boathouse Measured Section material indicates that much of tephra set S was erupted circa The Tacoma boathouse section is exposed at the base of an 80 ft 13,000 yr , but no radiocarbon dates are available for the base B.P. high bluff on the northeast side of Point Defiance (Fig. 3). The of set S at Mount St. Helens and the eruptions that produced the exposure is located about 7 mi west of the Hylebos Waterway set may have started before 13,650 yr (Mullineaux, 1996). B.P. sections. This section was originally mapped as undifferentiated Other workers have hypothesized that tephra set S could be as pre-Vashon nonglacial sediments beneath Vashon Drift by old as 16,000 years or that it may represent several distinct B.P. Smith (1977). The nonglacial sediments are exposed immediately above sea level and the contact with overlying Vashon Drift is only 52 ft MSL (Fig. 10). A peat bed in the nonglacial se-

UPLAND SURFACE quence yielded a radiocarbon age of >46,750 yr B.P. (Beta- 400 COVERED 80938). With only an infinite radiocarbon date available, these Vashon Drift sediments can not be correlated with any particular nonglacial Till overlying cross-bedded to laminated to COVERED massive sand with gravel interbeds, northern interval. Cascades lithologies

COVERED

300 Vashon Drift Till overlying cross-bedded to laminated to 300 massive sand with gravel interbeds, northern Cascades lithologies

)

on i 14C: 17,110 ±290 yrB.P. (Beta-89256)

Elevat Olympia beds 200 Gravel with mixed northern Cascades and volcanic lithologies, dated organic layer 200 underlies tephra at top springs on top of mudflow

)

L Sub-Olympia drift

S COVERED Massive oxidized gravel, northern Cascades

(f Olympia beds lithologies

i Volcanic, purple-gray sand (lahar runout) with tephra and peaty silt interbeds, pumaceous cl si fsms cs gr clasts

Elevat 14C: >46,450 yrB.P. (Beta-89875) Figure 9. Route 7 measured section, Tacoma South 7.5-minute quad- Sub-Olympia drift rangle, lat 47.2285 N, long 122.4262 W. Explanation on facing page. 100 Highly oxidized sand and gravel with northern Cascades lithologies UPLAND SURFACE 80 COVERED Vashon Drift

) Oxidized gravel with

S northern Cascades lithologies

planar bedded sand tM Nonglacial deposits

(f 40 Interbedded purple sand and silt with

on i diatomaceous sediment near top, predominantly volcanic lithologies

COVERED Elevat COVERED 14C: >46,750 yrB.P. (Beta-80938) 0 0 sand dikes, possible liquefaction features

cl si fsms cs gr cl si fs ms cs gr

Figure 8. Foran quarry measured section, Poverty Bay 7.5-minute Figure 10. Tacoma boathouse measured section, Gig Harbor 7.5- quadrangle, lat 47.2620 N, long 122.3536 W. Explanation on facing minute quadrangle, lat 47.3067 N, long 122.5146 W. Explanation on page. facing page. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 11

Sunset Beach Measured Section dicating that the sediments are probably younger than 780,000 The Sunset Beach section (Fig. 11) is exposed on a 200 ft high years B.P. (Troost and others, 1997). The radiocarbon date is cor- bluff on the east side of Puget Sound, 9 mi west-southwest of the relative with sediments deposited during the Olympia climatic Hylebos Waterway sections (Fig. 3). This exposure was origi- interval of the northern lowland. nally mapped by Walters and Kimmel (1968) as Vashon Drift. Based on the current study, two and possibly three glacial drift Subsurface Data sequences separated by fine-grained glaciolacustrine sediments Radiocarbon dates were obtained from samples from four bore- are exposed in the bluff. Thin Vashon till is present at the top of holes on McChord Air Force Base and the Fort Lewis Military the bluff and is underlain by a sandy outwash sequence. At 140 ft Reservation approximately 12 mi southwest of the Hylebos Wa- MSL, near the inferred base of the Vashon Drift, a fine-grained, terway sections and 3 mi east of the Solo Point section (Fig. 3). silty sand that is locally organic-matter-rich is exposed. Two The boreholes span about 5 mi from east to west. separate samples of wood from this fine-grained unit were ra- Borehole DA-2 is 320 ft deep and appears to intersect two or diocarbon dated, yielding ages of 13,620 ±80 yr B.P. (Beta- three glacial drift sequences (Appendix B, Fig. B-1). The upper 89876) and 12,960 ±180 yr B.P. (ISGS-3343). 85 ft is a Vashon Drift sequence of, from top to bottom, recessional outwash, till, advance outwash, and glaciolacustrine sedi- Solo Point Measured Section ments. Beneath the glaciolacustrine silt, 36 ft of fine to medium The Solo Point section is exposed on a 300 ft high bluff on the glacial sand were encountered. A date from a wood sample east side of Puget Sound about 14 mi southwest of the Hylebos found at 96 ft below ground surface (BGS) (204 ft MSL)inthe Waterway sections (Fig. 3). This exposure was originally glacial sand was >40,000 yr B.P. (I-15705). Between 121 and mapped as Vashon till over the Kitsap Formation by Walters and 320 ft BGS, interbedded till, outwash, and glaciolacustrine silt of Kimmel (1968). Vashon till is exposed at the top of the slope at a third outwash sequence may be present. Borehole DA-12e is 145 ft deep and was drilled about 1 mi approximately 300 ft MSL (Fig. 12). Much of the underlying west of DA-2 (Appendix B, Fig. B-2). The borehole passes slope is covered, but at 122 ft MSL there is a sharp contact between Vashon outwash and a thick nonglacial sequence. The through a Vashon Drift sequence and intersects older glacial nonglacial sediments are at least 92 ft thick and are composed of sediments. A wood sample collected 92 ft BGS (180 ft MSL)in interbedded lavender silt, fine-grained tephra, peat, and andes- glaciolacustrine sediments near the inferred base of the Vashon itic sand and gravel. A radiocarbon date obtained from a peat sequence has a date of 13,510 ±80 yr B.P. (Beta-79885). Vashon Drift above the glaciolacustrine sediments is represented by layer at 80 ft MSL yielded an age of 41,380 ±1940 yr B.P. (Beta 120064) (Troost, 1999). The silt is also normally magnetized in- interbedded outwash and till. A second wood sample collected

UPLAND SURFACE COVERED EXPLANATION 300 Vashon Drift Till overlying cross-bedded to laminated to cl clay massive sand and gravel with northern till silt si silt Cascades lithologies; oxidized at base; springs at contact with underlying fs fine sand sand peat Olympia beds ms medium sand cs coarse sand sandy gravel diamicton (lahar) gr gravel tephra COVERED

200 200

UPLAND SURFACE )

COVERED Vashon Drift S

Till overlying sand with gravel lenses, north- tM ern Cascades lithologies, glaciolacustrine (f

on silt at base with abundant woody debris i

14C: 12,960 ±180 yrB.P. (ISGS-3343) 13,620 ±80 yrB.P. (Beta-89876) Elevat

)

tM Sub-Olympia drift Olympia beds

(f 100 Oxidized sand and silt with northern Cascades 100 Predominantly volcanic lithologies, lavender

on i lithologies to purple-gray, pumaceous sand (lahar runout), many peat layers; laminated silt at top

Elevat 14C: 41,380 ±1940 yrB.P. (Beta-120064) – peaty silt

COVERED

0 0

cl si fs ms cs gr cl si fsms cs gr

Figure 11. Sunset Beach measured section, Steilacoom 7.5-minute Figure 12. Solo Point measured section, McNeil Island 7.5-minute quadrangle, lat 47.2232 N, long 122.5643 W. quadrangle, lat 47.1377 N, long 122.6310 W. 12 REPORT OF INVESTIGATIONS 33

48 ft lower than the first sample (132 ft MSL) in glacial silt and Lake. The fifth, cross section E–E¢ (Fig. 17), extends 4 mi west sand has a date of >41,300 yr B.P. (Beta-81801). The contact be- to the measured section at Solo Point on Puget Sound. tween Vashon Drift and the older drift sequence is believed to be The east–west cross sections show a relatively uniform at 98 ft BGS, where there is a sharp transition from gray clayey stratigraphic section that slopes gently to the west, but is com- silt above to a gray to brown-gray silty sand. monly disrupted by thick lenticular-shaped bodies of glacio- The log for borehole 4/6 is actually a composite of data from lacustrine silt (Figs. 13, 14, and 17). Based upon analyses of two wells that were drilled 1200 ft apart and reported by Noble samples from deep boreholes, these fine-grained sequences con- (1990) (Appendix B, Fig. B-3). The composite borehole is 295 ft tain little organic debris and are devoid of pollen (Estella B. deep and is located about 2.5 mi southwest of DA-12e. The bore- Leopold, Univ. of Wash., written commun., 1996). The lenticu- hole intersects three glacial drift sequences and three nonglacial lar bodies apparently fill glacial erosional troughs cut into the sequences. Our stratigraphic interpretation is similar to that of underlying sediments. Outside of these erosional troughs, the Noble (1990) except that some of the contacts between units glacial drift sequences are laterally continuous and of relatively have been adjusted after correlation with surrounding bore- uniform thickness. This more uniform stratigraphy is particu- holes. A radiocarbon date obtained from an organic-matter-rich larly evident on the north–south cross sections that do not inter- gravel with a mudflow texture and Mount Rainier source sect the deep erosional features (Figs. 15 and 16). In contrast to lithologies at about 60 ft BGS (210 ft MSL) yielded an age of the drift sequences, nonglacial units are relatively thin and dis- 25,100 ±600 yr B.P. (I-15,437). Based on this date, the gravel continuous as shown in cross section. most likely correlates with sediments deposited during the Olympia climatic interval. DISCUSSION Borehole MW-12 is 208 ft deep and was drilled about 2.5 mi west of borehole 4/6 (Appendix B, Fig. B-4). This borehole At least three glacial and three nonglacial units can be identified passes through three glacial drift units and one nonglacial se- in the sediments that occur above sea level in the study area. Pre- quence. A sample obtained from organic matter in silt at a depth vious mapping and borehole stratigraphic interpretations in the of about 60 ft (176 ft MSL) has a radiocarbon date of 13,630 ±90 study area generally identified only three or four units. The yr B.P. (Beta-52222). The organic-matter-rich silt is located near thickness, distribution, and age relationships of each of these the top of inferred Vashon glaciolacustrine sediments and is units is discussed in the following sections. For some units, we overlain by 60 ft of coarse Vashon outwash gravel and sand. present isopach and paleotopographic maps based upon the These radiocarbon-dated boreholes are connected with other borehole correlations described in Field and Laboratory Proce- boreholes by three east–west and two north–south cross sections dures (p. 4). (Fig. 2 and Figs. 13–17). All of the cross sections have a vertical exaggeration of 20 times in order to emphasize contact relation- Vashon Drift (Qv) ships and the geometry of paleotopographic surfaces. Four of Vashon Drift covers the surface of most of the study area. The the cross sections (Figs. 13–16) traverse the part of the study drift sequence varies between 40 and 260 ft thick in the bore- area with the highest borehole density to the east of American

A A¢ West East 0 2000 ft T-09 cross section C–C¢ CW-34 350 horizontal scale 350 vertical exaggeration 20x bend in section

DA-02 Interstate 5 bend in section TZ-01 DA-12 300 DA-16 DZ-06 DA-07 GC 300 DA-12e DA-25 T-12 DA-20 Poe + McGuire TZ-02 W1 Qv 250 250

Qob 200 Qv 14C 200 (>40,000 yrBP . .,I -15,705) Qpog Qpon

14 150 Qob C 150 (13,510 ±80 yr . ., Qpog BP b-79885) 14C (>41,300 yrBP . ., Qpog2

Elevation (ft MSL) b-81801) 100 100 Qpon

Qpog 50 2 50

Qpog2

0 0

Qpon Qpog 2 -50 2 -50 Figure 13. Cross section A–A¢. Explanation on facing page. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 13 holes and measured sections. Older stratigraphic units crop out sections. Many of these glaciolacustrine sediments are herein only in cliffs along Puget Sound and in deeply incised river val- correlated with the Lawton Clay, whose type section is in the Se- leys and gullies. Vashon Drift is dominated by advance and re- attle area (Mullineaux and others, 1965). cessional outwash with discontinuous glaciolacustrine sedi- Beneath most of the subsurface study area (Fig. 3), the base ments at the base and discontinuous till towards the top of the se- of the Vashon Drift slopes gently to the north and west, and is in quence. Basal glaciolacustrine sediments were encountered in contact with either the Olympia beds or an older glacial drift se- about 20 percent of the boreholes and in one of the measured quence. This relatively uniform surface is disrupted by at least

EXPLANATION B B¢ West East Stratigraphic designations cross section D–D¢ (delineated by bold lines) bend in section Well 8 cross section C–C¢ Qv Vashon Drift LC-73 LC-26 Qob Olympia beds LC-41 300 LC-65 LC-35 LC-19 300 Qpog Pre-Olympia glacial drift LC-70 LC-69 LC-21 LC-64 Second nonglacial deposits RD-1 Qpon LC-67 Qpog2 Third glacial drift Qpon Third nonglacial deposits 2 250 250 Lithologic symbols

Qv till 200 Qpog 200 Qob

glaciolacustrine deposits Qpog Qpon

glacial 150 150

sand/gravel outwash Qpon (typically water-bearing) Qpog2 100 100 coarse-grained

fluvial sediments Elevation (ft MSL) (typically water-bearing) Qpog 50 2 50 fine-grained fluvial/ lacustrine sediments

nonglacial Qpon2 mudflow deposits 0 0 2000 ft 0 horizontal scale vertical exaggeration 20x Contacts are dashed where approximate -50 -50 Bold borehole numbers indicate Figure 14. Cross section B–B¢. samples examined for this study

C C¢ bend in section North bend in section South DA-26 cross section A–A¢ cross section B–B¢

DA-15 LZ-04 LC-22 LC-50 Well 5001 DA-12e LC-55 300 DA-18 LC-21 300 DA-13 W3 W4

250 250

200 200 Qob Qpog (13,510 ±80 yrBP . .,b -79,885) 14C 150 Qpon 150 (>41,300 yrBP . .,b -81,801) 14C

100 100

Elevation (ft MSL)

50 Qpog2 50

0 Qpon 0 2 0 2000 ft horizontal scale vertical exaggeration 20x -50 -50 Figure 15. Cross section C–C¢. 14 REPORT OF INVESTIGATIONS 33 one deep trough that is oriented north–south and is traceable for 12e (Troost and Borden, 1996). The four radiocarbon dates yield over a mile in the subsurface (Fig. 18). The base of the trough an average age of 13,430 yr B.P., which is about 1,000 years cuts downsection all the way to the third glacial drift unit. The younger than is generally assumed for the advance of Vashon ice Vashon Drift sequence is typically 100 ft thick in the subsurface into the south-central lowland. This seeming anomaly requires study area, but thickens to as much as 230 ft in the center of the that either (1) all four samples had been contaminated with trough. Based upon crosscutting relationships, the vertical con- younger organic matter, (2) few Vashon advance sediments are tinuity of glacial sediments in the trough, and a single radiocar- preserved in the study area and the radiocarbon samples were bon date of 13,510 ±80 yr B.P. (Beta-79885) (borehole DA-12e), collected from recessional glaciolacustrine sediments, or (3) the the trough is thought to have been cut and filled during Vashon samples were collected from Vashon advance sediments and time. Vashon glaciation began much later in the south-central lowland Four radiocarbon dates are reported herein from glacio- than is commonly believed. lacustrine sediments near the inferred base of the Vashon Drift It is unlikely that all four samples were contaminated with (Table 3). These samples were obtained from three widely younger organic matter. Three of the samples, collected from spaced locations. Vashon outwash overlies the sampling points three different locations and analyzed in three different years, at all three locations and Vashon diamicton has been identified have ages within 120 years of each other and an average age of above the sampling points at Sunset Beach and in borehole DA- 13,590 yr B.P. (Table 3, samples Beta-79885, Beta-89876, and

EXPLANATION D D¢ North South Stratigraphic designations bend in section (delineated by bold lines) cross section A–A¢ bend in section Qv Vashon Drift Well 4/6 Comp T-11 bend in section cross section B–B¢ Qob Olympia beds T-02 LC-61 Qpog Pre-Olympia glacial drift 300 300 T-10 LC-60 Qpon Second nonglacial deposits T-09 LC-71 LC-72 LC-73 Qpog2 Third glacial drift Qpon2 Third nonglacial deposits 250 250 Lithologic symbols (25,100 ±600 yrBP . .,I -15,437) 14C till 200 Qv 200 Qob Qob glaciolacustrine deposits

glacial 150 Qpog 150 sand/gravel outwash (typically water-bearing) Qpon

coarse-grained 100 100 0 2000 ft

fluvial sediments Elevation (ft MSL) (typically water-bearing) horizontal scale Qpog vertical exaggeration 20x fine-grained fluvial/ 50 2 50 lacustrine sediments

nonglacial

mudflow deposits 0 0

Contacts are dashed where approximate Qpon2 -50 -50 Bold borehole numbers indicate samples examined for this study Figure 16. Cross section D–D¢.

E E¢ North bend in section East 0 4000 ft cross section C–C¢ horizontal scale cross section D–D¢ bend in section LC-26 vertical exaggeration 20x bend in section LC-35 400 Well 8 400 LC-41 PUGET bend in section LC-21 SOUND RD-1 LC-65 bend in section LF4-MW3B LC-70 LF4-MW16B AMERICAN LAKE LC-64 Solo LC-69 LC-19 300 bend in section LC-73 LC-67 300 Point LF4-MW4 LF4-MW1B 88-5-SS 88-1-SS LF4-MW6SB Qob Qpog 200 Qv 200 Qv Qpog Qpon Qpon 100 Qob 100 Elevation (ft MSL) ? Qpon

Qpog2 0 0 Qpon2 Qpon2 -50 -50 Figure 17. Cross section E–E¢. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 15

Beta-52222). If these anomalously young dates were a result of ence of organic matter beneath pure diatomite at the base of ket- contamination, it would require that all three samples contain tle-fill deposits in the Nooksack drainage in the northern Puget about the same percentage of younger organic material, which is Lowland. However, the limited size of the Sunset Beach expo- unlikely. Two of these three samples were collected from more sure makes it difficult to determine if it is part of a larger kettle than 60 ft below the ground surface, so there would have been complex, and it is unclear if this mechanism can explain the little opportunity for contamination by younger material. The presence of anomalously young organic debris beneath thick fourth date, obtained from a wood fragment that was collected at well-sorted outwash sediments. the Sunset Beach exposure to confirm a date previously ob- There are few constraining dates available south of Seattle to tained from the same exposure, was about 600 years younger document the advance of the Vashon ice sheet (Booth, 1987). than the other three (Table 3, sample ISGS-3343). Early radiocarbon dates from the Seattle area, 25 mi north of the The dates reported here are consistent with Vashon reces- present study area, indicated that the Vashon ice front arrived sional dates obtained from several locations in the north and there sometime after 15,000 years B.P. (Mullineaux and others, central lowland (Rigg and Gould, 1957; Yount and others, 1980; 1965; Deeter, 1979). Seven recently published dates from Leopold and others, 1982; Easterbrook, 1986; Anundsen and Vashon advance outwash in the Seattle area average 14,546 ±28 others, 1994; Dethier and others, 1995). The dates presented by 14CyrB.P. (Porter and Swanson, 1998). If the young dates re- these authors were generally derived from peat bog, lacustrine, ported in the current study are from Vashon advance sediments, or glaciomarine sediments deposited during or shortly after the this would imply that the ice front required about 1,000 years to recession of the Vashon ice sheet. If the samples in the current move from the Seattle to the Tacoma area. Previous workers study were also collected from recessional sediments, it would have postulated a more rapid rate of advance because of the con- require that at three widely separated locations in the Tacoma straining ages obtained from post-Vashon sediments throughout area, (1) little or no Vashon advance sediments are present, (2) the lowland. Rigg and Gould (1957) published a commonly ref- vegetation was growing nearby during the recessional period, erenced date of 13,650 yr B.P. (their sample number L-346a) for and (3) the radiocarbon-dated material was buried beneath 60 to post-Vashon sediments in Lake Washington near Seattle. Many 90 ft of Vashon recessional sediments after it was deposited. It subsequent studies have yielded maximum constraining dates of would also require that the till capping the bluff at Sunset Beach around 13,500 yr B.P. for the retreat of Vashon ice from the low- (Fig. 11) is an ablation till underlain by 85 ft of Vashon reces- land (Yount and others, 1980; Leopold and others, 1982; sional outwash. Porter and Carson (1971) noted that younger or- Easterbrook, 1986; Anundsen and others, 1994; Dethier and oth- ganic matter may be incorporated into older recessional glacial ers, 1995). Clearly, an age of 13,500 yr B.P. for the Vashonretreat sediments when drift-mantled stagnant ice melts away and is not compatible with the new radiocarbon dates provided by causes material to collapse into underlying voids. Kovanen and this study if they were actually collected from Vashon advance Easterbrook (2001) cited the same process to explain the pres- sediments. For both sets of dates and interpretations to be cor-

160 McCHORD railroad tracks AIR FORCE FORT 5 BASE LEWIS

MILITARY 175 174 197 182 RESERVATION 192 174 184 185 175 181 American Lake 125 180 211 200 111 50 212 199 219 167 210 180 174 198 224 46 217 206 <122 208 217 214 200 179 201 183 62 215 200 245 208 204 50 223 225 173 199 185 0 3000 ft 175 194 201 159 scale 176 195 200 184 88 EXPLANATION 181 175 123 166 Boring location with elevation of 200 184 83 52 92 182 contact in feet above mean sea level

75 200 Paleotopographic contour FORT LEWIS 217 210 150 (dashed where approximate;

125 175 100 75 186 100 hatch marks indicate a depression 100 178 MILITARY RESERVATION 150 in the surface)

Figure 18. Paleotopographic map of the base of the Vashon Drift (unit Qv). 16 REPORT OF INVESTIGATIONS 33

160 McCHORD railroad tracks AIR FORCE 0 3000 ft 5 FORT BASE scale LEWIS 175 174 MILITARY 197 182 RESERVATION 192 174

184 181 185 American Lake 219 180 200 174 206 212 211 167 199 198 224 150 208 172 207 225 217 184 206 217 179 183 215 201 214 215 244 208 204 200

125 223 199 173 184 150 EXPLANATION 194 201 159 Paleotopographic contour 195 100 (dashed where approximate) 176 175 200 184 181 Area where unit is not present 166 Boring Locations and Nature of Upper Contact 171 (with elevation of contact in feet above mean sea level) FORT LEWIS 175 Overlain by Olympia-beds nonglacial fluvial sediments 195 150 175 Overlain by Olympia-beds mudflow deposits 175 186 MILITARY RESERVATION 178 Overlain by Vashon glaciolacustrine sediments 175 Abrupt change from gravel-dominated glacial outwash above to sand-dominated glacial outwash(commonly oxidized) below

Figure 19. Paleotopographic map of the top of the pre-Olympia drift (unit Qpog).

61?

railroad tracks McCHORD

AIR FORCE FORT 5 BASE LEWIS

75 MILITARY 69 110? RESERVATION 87 26 >59 64 American Lake 104 80 0 >88 100 100 56 56 85 0 12 44 0 0 36 75 67

0 35 47 50 0 3000 ft 36 35 43 38 25 scale 51 41 0 EXPLANATION 47 38 0 0 Boring location with 44 50 thickness of unit in feet 3? 0 0 32 0 Isopach contour (dashed FORT LEWIS 50 where approximate) 10

25 Area where unit is not 26 14 MILITARY RESERVATION 0 present

Figure 20. Isopach map of the pre-Olympia drift (unit Qpog). LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 17 rect it would require the Vashon ice sheet to be advancing to its Based upon its character and stratigraphic position directly terminus in the southern lowland at the same time that post-gla- beneath the Olympia beds, this unit may correlate with the Pos- cial sediments were beginning to accumulate in the north and session Drift. The Possession Drift in the northern lowland has central lowland. We do not feel that this issue will be fully re- been dated at about 80,000 yr B.P. by amino-acid analysis of ma- solved until additional constraining age dates for the Vashon ad- rine shells (Easterbrook, 1994). The older outwash sequence in vance have been obtained from the southern Puget Lowland. the Tacoma area has seldom been differentiated from the overlying Vashon advance outwash because: (1) Olympia and Lawton Olympia Beds (Qob) Clay marker beds are rarely present in the section and are difficult to recognize where they are present, (2) as a glacial drift it Nonglacial sediments deposited during the Olympia climatic in- generally resembles the overlying Vashon advance outwash, and terval are locally present throughout the study area but have (3) in the study area, it does not contain an associated glacial till. variable thickness and are discontinuous. They are generally If the Possession glacial maximum was located at or north of the represented by lahars, ashes, and fine-grained fluvial sediments. Tacoma area, this would explain both the scarcity of till and the The Olympia beds were identified at the Hylebos Waterway, relatively low-energy outwash sediments that dominate the in- Route 7, and Solo Point measured sections, and in the subsur- ferred Possession sequence in the subsurface study area imme- face study area. Probable Olympia beds were identified in about diately to the south of that glacial maximum. 10 percent of the boreholes that were examined (see Fig. 19). In The characteristics and stratigraphic relationships of the pre- the boreholes, Olympia beds were encountered between 170 and Olympia drift are very similar to the description of the Colvos 220 ft . In the measured sections, the Olympia beds were ex- MSL Sand made by Garling and others (1965). The Colvos Sand is de- posed as high as 240 ft at Hylebos Waterway in the north to MSL scribed as a laterally continuous sandy outwash sequence imme- perhaps as low as sea level at Solo Point in the south. diately beneath and in sharp, sometimes unconformable contact Finite radiocarbon dates obtained from the Olympia beds in with the overlying gravelly Vashon advance outwash. Garling the study area range from 17,000 to 41,000 yr (Troost and B.P. and others (1965) assumed that the Colvos Sand was an early Borden, 1996). Several samples from inferred Olympia sedi- phase of Vashon glaciation, but many of the outwash sequences ments have infinite radiocarbon ages of up to >46,000 yr designated as Colvos Sand in the Tacoma area may actually be Previously published radiocarbon dates from Olympia sed- B.P. correlative with the pre-Olympia drift or an older glacial drift. iments elsewhere in the lowland and in southwestern British Co- lumbia are consistent with these dates. Finite dates ranging from Second Nonglacial Deposits (Qpon) 15,000 to 40,500 yr B.P. and perhaps as old as 58,800 yr B.P. have been reported (Deeter, 1979; Mullineaux and others, 1965; A second nonglacial interval is commonly present in the Hansen and Easterbrook, 1974; Armstrong and others, 1965; subsurface study area beneath the pre-Olympia drift, but was not Clague, 1981). positively identified in any of the measured sections. In general, the second nonglacial deposits are present only in the southern Pre-Olympia Drift (Qpog) half of the subsurface study area (Fig. 21). In the northern half, they tend to be missing in areas where the overlying pre-Olym- A thick and laterally continuous fine-grained glacial outwash pia drift is thickest. The nonglacial sediments are also missing sequence underlies the Olympia beds throughout the subsurface within the Vashon erosional trough. Where present, the top of study area, but may not be present beneath the Olympia beds at the second nonglacial deposits slopes gently to the west. In the the Hylebos Waterway and Route 7 measured sections to the south, the surface elevations vary between about 120 and 170 ft north. No associated till was identified in any of the boreholes or . In the north, a single isolated occurrence of the second measured sections examined during this study, although till has MSL nonglacial deposits has a surface elevation of only 100 ft . been encountered in outcrops of inferred pre-Olympia drift else- MSL Outside of the erosional areas, the second nonglacial sediments where in the Tacoma area (Troost and others, 1997). vary between about 10 and 40 ft in thickness (Fig. 22). Two radiocarbon-dated samples from inferred pre-Olympia Based upon their character and stratigraphic position as the drift yielded ages of >40,000 yr and >41,300 yr B.P. (Table B.P. next oldest nonglacial sequence beneath the Olympia beds, 3, samples I-15705 and Beta-81801). These dates are at least many of the second nonglacial deposits encountered during this 25,000 years older than the Vashon Drift. study may correlate with the Whidbey Formation of the northern In the subsurface, this outwash was differentiated from over- lowland. In the northern lowland, the Whidbey Formation is lying Vashon advance outwash by one or more of the following: thick, laterally continuous, and separated from the Olympia (1) the presence of intervening Olympia beds, (2) the presence beds by a single glacial drift unit, the Possession Drift (Easter- of intervening glaciolacustrine sediments, (3) an abrupt change brook and others, 1967). The Whidbey Formation has been from a gravel-dominated glacial outwash above to a sand-domi- dated to about 100,000 yr in the northern lowland by amino- nated glacial outwash below, and (4) the presence of a thin, mod- B.P. acid analyses and thermoluminescence (Easterbrook, 1994). erately to intensely oxidized zone at the top of the sand-domi- Other studies have correlated the second nonglacial sedi- nated sequence. The transition between the overlying gravelly ments of the subsurface study area with the nonglacial sedi- Vashon outwash and the underlying sand-dominated glacial se- ments that crop out at sea level over much of the Tacoma area quence is typically very sharp. A paleotopographic map of the (Brown and Caldwell, Inc., and others, 1985; Noble, 1990). In top of the pre-Olympia drift was generated according to the the past, these exposures were identified as the Kitsap Clay or above criteria (Fig. 19). The top surface of the drift slopes gently the Kitsap Formation and were assumed to be related to the to the north and west. Elevations vary between 160 and 240 ft Olympia climatic interval (Sceva, 1957; Garling and others, except on the margins of the Vashon erosional trough. No MSL 1965; Walters and Kimmel, 1968). However, at different loca- pre-Olympia drift occurs within this erosional feature, but out- tions the sea-level nonglacial exposures may actually correlate side the trough, drift sequences more than 100 ft thick were en- to the Olympia beds (as at Solo Point), the Whidbey Formation, countered in some boreholes (Fig. 20). or an older nonglacial interval (as at Woodworth quarry) (Troost 18 REPORT OF INVESTIGATIONS 33

McCHORD

AIR FORCE railroad tracks BASE

FORT 5

LEWIS

MILITARY

RESERVATION

100 American Lake 127

116 173

138 152 03000ft

148 scale 124 151 163 EXPLANATION 125 154 135 Boring location with elevation of 145 152 125 143 contact in feet above mean sea level 168 Paleotopographic contour 150 (dashed where approximate; 163 FORT LEWIS 165 150 hatch marks indicate a depression 150 in the surface) 172 MILITARY RESERVATION 153 Area where unit is not present

Figure 21. Paleotopographic map of the top of the second nonglacial deposits (unit Qpon).

0 McCHORD railroad tracks AIR FORCE

BASE FORT 5 LEWIS

MILITARY 0 0 RESERVATION 0 0

0 0 American Lake 22 14 0 0 0

0 0 14 25 0 0

0 0 0 0

28 13 0 3000 ft 26 30 32 18 scale 20 24 30 30 EXPLANATION 0 17 Boring location with 25 28 thickness of unit in feet 26 0 0 0 Isopach contour FORT LEWIS 44 17 25 (dashed where approximate)

0 14 Area where unit is 25 33 MILITARY RESERVATION 0 not present

Figure 22. Isopach map of the second nonglacial deposits (unit Qpon). LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 19 and others, 1997; Booth and Waldron, in press). Correlation be- per Salmon Springs type section to the east (Crandell and others, tween the subsurface study area and the sea cliff exposures is 1958), at Penultimate drift exposures to the south (Lea, 1984), difficult under these circumstances and the use of the term “Kit- and at Qc3 drift exposures in King County immediately north of sap Formation” would be misleading. the study area (South King County Groundwater Advisory Com- mittee and others, 1991). Some of these drift sequences may cor- Third Glacial Drift (Qpog2) relate with the Double Bluff Drift of the northern lowland. The Double Bluff Drift has been dated to between 150,000 and The third glacial drift encountered in the subsurface study area 250,000 years in the northern lowland (Easterbrook, 1994). is characterized by an oxidized drift sequence whose upper sur- B.P. In the north, the Double Bluff Drift, like our third glacial drift, is face is near sea level. In the subsurface study area, this drift un- the third glacial drift in the sequence, is commonly oxidized, derlies the second nonglacial deposits, but at the Hylebos Wa- and is exposed at sea level (Easterbrook and others, 1967). terway measured sections it may directly underlie the Olympia beds. Third Nonglacial Deposits (Qpon ) In the subsurface, the third glacial drift is a 150 ft thick se- 2 quence of advance and recessional outwash with interbedded till A third set of nonglacial sediments was encountered in several deposits. In boreholes, these glacial deposits were distinguished of the deep boreholes in the subsurface study area. The upper from younger drift sequences by one or more of the following: surface of these nonglacial sediments slopes moderately to the (1) the presence of intervening second nonglacial sediments, (2) northwest and varies between about 50 and -40 ft MSL (Fig. 24). the presence of intervening glaciolacustrine sediments, and (3) The thickness of this unit is not known because its lower contact the presence of a thick, intensely oxidized zone at the top of the was not identified in any of the boreholes. third glacial recessional outwash. In one location, till occurs at Based upon their stratigraphic position in the subsurface the top of the third glacial drift sequence (Fig. 13, eastern end of study area, these sediments are assumed to be older than the cross section A–A¢). This point is also a topographic high on the Whidbey Formation and to be pre–late Pleistocene in age. The paleosurface and may represent a buried drumlin-like feature reversely magnetized nonglacial sediments exposed at the base (Fig. 23). Outside of the Vashon erosional trough, the upper sur- of the Woodworth quarry measured section on Hylebos Water- face of the drift slopes gently to the north and west with eleva- way are likely older than 780,000 years and so are also probably tions ranging from as high as 179 ft to as low as 102 ft MSL. The older than the Whidbey Formation. Recent work at this out- Vashon erosional trough is incised almost 100 ft through the crop has yielded a preliminary fission track date of 1,100,000 original paleotopographic surface on top of the third glacial ±150,000 yr B.P. (Richard J. Stewart, Univ. of Wash., written drift. commun., 1999). The stratigraphic position and character of the third glacial drift is similar to highly oxidized drift sequences noted at the up-

120 railroad tracks McCHORD

AIR FORCE

FORT 124 5 BASE LEWIS

MILITARY 113 130

RESERVATION 105 125 148

117 100 American Lake 78 114 102 50 111 <123

101 111 102 121 46 148 179 62 175 150 133 50 110 125 0 3000 ft 122 121 106 125 131 scale 105 124 115 111 88 EXPLANATION 126 123 Boring location with elevation of 115 83 52 92 142 contact in feet above mean sea level 119 FORT LEWIS Paleotopographic contour 75 148 (dashed where approximate;

100 75 139 100 hatch marks indicate a depression 139 MILITARY RESERVATION 100 in the surface) 125

Figure 23. Paleotopographic map of the top of the third glacial drift (unit Qpog2). 20 REPORT OF INVESTIGATIONS 33

railroad tracks McCHORD

AIR FORCE FORT 5 BASE LEWIS -25 MILITARY -14 <-17 RESERVATION -32

-39 American Lake

-37

<-40 <-38

<-33 <-20

<-25

03000ft

scale <-20 -50 EXPLANATION

51 Boring location with elevation of -25 51 FORT LEWIS contact in feet above mean sea level 0 <63 Paleotopographic contour -25 50 25 (dashed where approximate) MILITARY RESERVATION 50

Figure 24. Paleotopographic map of the top of the third nonglacial deposits (unit Qpon2).

Hydrogeologic Implications The nature and distribution of these gla- Vashon recessional Interbedded, brown to gray sandy gravel and sand with cial and nonglacial units has a profound outwash, unit Qv minor silt interbeds influence on ground-water flow and Vashon till and Dense, gray, silty sandy gravel and gravelly sandy silt, Discontinuous contaminant movement in the Quater- ice contact generally matrix supported aquitard deposits, unit Qv nary sequence beneath the study area. As shown on Figure 25, glacial drift se- Vashon advance Interbedded, brown to gray sandy gravel and sand with outwash, unit Qv minor silt interbeds quences tend to act as aquifers because they are dominated by sand and gravel Glaciolacustrine silt/clay Gray, laminated to massive silt and clayey silt with minor Discontinuous outwash deposits. Conversely, non- (Lawton Clay), unit Qv fine sand interbeds aquitard glacial sediments tend to act as aqui- Olympia beds, Mottled, massive, organic-rich, clayey, sandy gravel tards because of their generally fine- (mudflows) or lavender silt, peat, sand, and gravelly sand Discontinuous unit Qob aquitard Vashon unconfined aquifer (fluvial and overbank deposits) (17,110 to >46,450 yrBP . .) grained nature. However, these general- Gray-brown, fine to medium-grained sand with minor izations are not everywhere correct. Pre-Olympia drift, sandy gravel interbeds, oxidized at top; common silt unit Qpog Glacial drift units locally contain dis- interbeds at base, rare and discontinuous till continuous aquitards such as till and Mottled, massive, organic-rich, clayey, sandy gravel Aquitard Second nonglacial (mudflows) or lavender silt, peat, sand, and gravelly sand (locally breached by unitQv and glaciolacustrine sediments, and non- deposits, unit Qpon (fluvial and overbank deposits) Qpog erosional features) glacial sediments locally contain perme- Interbedded, orange to dark gray sandy gravel and sand able alluvial sand and gravel layers. with minor silt interbeds, intensely iron-oxide stained at top The sediment package generally considered to comprise the Vashon un- Third glacial drift, Dense, gray, silty, sandy gravel and gravelly, sandy silt, Discontinuous confined aquifer by hydrogeologists unit Qpog2 generally matrix supported (till) aquitard

aquifer

Sea level working in the Tacoma area actually Interbedded, gray-brown to dark gray sandy gravel and contains two distinct glacial intervals sand with minor silt interbeds and one nonglacial interval. Discontinu- Third nonglacial Lavender silt, peat, sand, and gravelly sand (fluvial and ous aquitards associated with the Aquitard deposits, unit Qpon2 overbank deposits) Vashon till, Lawton Clay, and Olympia beds are all contained within the uncon- Figure 25. Generalized stratigraphic and hydrostratigraphic column for west-central Pierce fined aquifer. Regionally, all of the sedi- County. Shaded units generally act as aquitards. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 21 ments above the second nonglacial deposits probably do act as a Environmental Corporation and Shannon & Wilson, Inc., for single aquifer system, but locally these discontinuous aquitards providing logs and saving sediment samples from many bore- may impede the vertical movement of water and contaminants. holes; Dr. Jack Liu and the Illinois State Geological Survey for These aquitards may also perch groundwater above the regional providing a free radiocarbon analysis for quality assurance; water table and locally influence the rate and direction of hori- Timothy Walsh and Dr. Stephen Palmer of the Washington Di- zontal groundwater flow. vision of Geology and Earth Resources (DGER) and John Noble The second nonglacial sediments are relatively continuous of Robinson and Noble, Inc., for their geologic expertise and in- beneath the Tacoma area and are typically thought to isolate the sight into the stratigraphy of Pierce County; Pat Pringle of upper unconfined aquifer from a confined aquifer that is present DGER for his help with the tephra sample from the Route 7 ex- near sea level. However, in some areas the aquitard is breached posure; and quarry owners near the Port of Tacoma for access on by deep erosional features associated with younger glacial private property. The authors also wish to thank Dr. Don events. In these areas there may be little to impede the vertical Easterbrook (Western Wash. Univ.), Dr. Derek Booth (Univ. of movement of water and contaminants between the two aquifer Wash), Timothy Walsh and Wendy Gerstel (DGER), and Dr. systems. Figure 14 shows the erosional feature that truncates the Ray Wells (U.S. Geological Survey) for reviewing earlier ver- second nonglacial deposits in the subsurface study area. Most of sions of this manuscript. The work was conducted as part of an the trough is filled with fine-grained glaciolacustrine sediments, independent research project by the authors. so it generally maintains the laterally continuity of the aquitard. However, a sandy sequence on the western side of the trough REFERENCES CITED provides a pathway for water movement between the unconfined and confined aquifers. This permeable sequence may also Anundsen, Karl; Abella, S. E. B.; Leopold, E. B.; Stuiver, Minze; have provided a conduit for trichloroethylene contamination Turner, Sheila, 1994, Late-glacial and early Holocene sea-level that is widespread in the upper aquifer to enter the lower aquifer fluctuations in the central Puget Lowland, Washington, inferred (Borden and Troost, 1994). from lake sediments: Quaternary Research, v. 42, no. 2, p. 149- 161. CONCLUSIONS Armstrong, J. E.; Brown, W. L., 1954, Late Wisconsin marine drift and associated sediments of the lower Fraser Valley, British Co- The identification of widespread sediments deposited during the lumbia, Canada: Geological Society of America Bulletin, v. 65, Olympia climatic interval and an additional underlying glacial no. 4, p. 349-364. outwash sequence in the Tacoma area allows the late Pleisto- Armstrong, J. E.; Crandell, D. R.; Easterbrook, D. J.; Noble, J. B., cene stratigraphic nomenclature in the northern and south-cen- 1965, Late Pleistocene stratigraphy and chronology in southwest- tral Puget Lowlands to be tentatively reconciled. The proposed ern British Columbia and northwestern Washington: Geological youngest to oldest late Pleistocene sequence in the south-central Society of America Bulletin, v. 76, no. 3, p. 321-330. lowland is Vashon Drift (with Lawton Clay as its basal unit), Beget, J. E.; Keskinen, M. J.; Severin, K. P., 1997, Tephrochronologic Olympia beds, pre-Olympia drift (possibly Possession Drift), constraints on the late Pleistocene history of the southern margin and a second nonglacial unit (possibly Whidbey Formation). At of the Cordilleran ice sheet, western Washington: Quaternary Re- some locations, an oxidized third glacial drift may also be late search, v. 47, no. 2, p. 140-146. Pleistocene in age if it is correlative with the Double Bluff Drift. Blunt, D. J.; Easterbrook, D. J.; Rutter, N. W., 1987, Chronology of The third nonglacial deposits are likely pre–late Pleistocene in Pleistocene sediments in the Puget Lowland, Washington. In age. All of these units are present in the Tacoma area, although Schuster, J. E., editor, Selected papers on the geology of Washing- at any given location one or more may be missing. The use of the ton: Washington Division of Geology and Earth Resources Bulle- term “Kitsap Formation” for the first and (or) second nonglacial tin 77, p. 321-353. sediments should be discontinued because throughout the his- Booth, D. B., 1987, Timing and processes of deglaciation along the tory of its usage, it has been applied to nonglacial sediments of southern margin of the Cordilleran ice sheet. In Ruddiman, W. F.; nearly all ages. The stratigraphic framework in the Tacoma area Wright, H. E., Jr., editors, North America and adjacent oceans is thus much more complicated than previously described. This during the last glaciation: Geological Society of America DNAG complexity has significant implications for regional hydro- Geology of North America, v. K-3, p. 71-90. geologic models, structural interpretation, and evaluation of Booth, D. B., 1994, Glaciofluvial infilling and scour of the Puget geologic hazards. Lowland, Washington, during ice-sheet glaciation: Geology, The inferred base of the Vashon Drift in the study area is v. 22, no. 8, p. 695-698. sometimes represented by fine-grained glaciolacustrine sedi- Booth, D. B.; Waldron, H. H., in press, Surficial geologic map of the ments with an average age of 13,430 years B.P. This is about Des Moines 7.5-minute quadrangle, King County, Washington: 1,000 years younger than is generally assumed for the inception U.S. Geological Survey Miscellaneous Field Studies Map, of Vashon glaciation in the south-central lowland but is consis- 1 sheet, scale 1:24,000. tent with Vashon recessional dates reported by other workers. This implies that either 1) almost all of the Vashon sediments in Borden, R. K., 1998, Report accompanying geologic map of Naval the study area are recessional in age or 2) Vashon glaciation in Submarine Base Bangor. In Kahle, S. C., 1998, Hydrogeology of Naval Submarine Base Bangor and vicinity, Kitsap County, the south-central lowland began much later than is commonly Washington: U.S. Geological Survey Water-Resources Investiga- believed. tions Report 97-4060, p. 85-107, 1 plate. Borden, R. K.; Troost, K. G., 1994, The influence of stratigraphy and ACKNOWLEDGMENTS depositional environment on trichloroethylene movement in a The authors thank Shannon & Wilson, Inc., for providing funds multiple aquifer system [abstract]: Geological Society of America for radiocarbon dating and supplying graphics and clerical sup- Abstracts with Programs, v. 26, no. 7, p. A436. port for this publication; the geologists of both Foster Wheeler 22 REPORT OF INVESTIGATIONS 33

Borden, R. K.; Troost, K. G., 1995, Hydrogeologic implications of re- Huntting, M. T.; Bennett, W. A. G.; Livingston, V. E., Jr.; Moen, fined central Pierce County stratigraphy [abstract]. In Washing- W. S., 1961, Geologic map of Washington: Washington Division ton Department of Ecology, Abstracts from the 1st symposium on of Mines and Geology Geologic Map, 2 sheets, scale 1:500,000. the hydrogeology of Washington State: Washington Department Jones, M. A., 1996, Thickness of unconsolidated deposits in the Puget of Ecology, p. 117-118. Sound lowland, Washington and British Columbia: U.S. Geologi- Bretz, J H, 1913, Glaciation of the Puget Sound region: Washington cal Survey Water-Resources Investigations Report 94-4133, Geological Survey Bulletin 8, 244 p., 3 plates. 1 sheet, scale 1:455,000. Brown and Caldwell, Inc.; Sweet, Edwards & Associates; Robinson & Kovanen, D. J.; Easterbrook, D. J., 2001, Late Pleistocene, post- Noble, Inc., 1985, Clover/Chambers Creek geohydrologic study; Vashon, alpine glaciation of the Nooksack drainage, North Cas- Final report: Tacoma-Pierce County Health Department, 1 v. cades, Washington: Geological Society of American Bulletin, Clague, J. J., 1981, Late Quaternary geology and geochronology of v. 113, no. 2, p. 274-288. British Columbia; Part 2—Summary and discussion of radiocar- Lea, P. D., 1984, Pleistocene glaciation at the southern margin of the bon-dated Quaternary history: Geological Survey of Canada Pa- Puget lobe, western Washington: University of Washington Mas- per 80-35, 41 p. ter of Science thesis, 96 p., 3 plates. Clark, P. U., 1992, The last interglacial-glacial transition in North Leopold, E. B.; Nickmann, R. J.; Hedges, J. I.; Ertel, J. R., 1982, Pol- America—Introduction. In Clark, P. U.; Lea, P. D., editors, 1992, len and lignin records of late Quaternary vegetation, Lake Wash- The last interglacial-glacial transition in North America: Geologi- ington: Science, v. 218, no. 4579, p. 1305-1307. cal Society of America Special Paper 270, p. 1-11. Mullineaux, D. R., 1970, Geology of the Renton, Auburn, and Black Crandell, D. R.; Mullineaux, D. R.; Waldron, H. H., 1958, Pleistocene Diamond quadrangles, King County, Washington: U.S. Geologi- sequence in southeastern part of the Puget Sound lowland, Wash- cal Survey Professional Paper 672, 92 p. ington: American Journal of Science, v. 256, no. 6, p. 384-397. Mullineaux, D. R., 1986, Summary of pre-1980 tephra-fall deposits Crandell, D. R.; Mullineaux, D. R.; Waldron, H. H., 1965, Age and or- erupted from Mount St. Helens, Washington State, USA: Bulletin igin of the Puget Sound trough in western Washington: U.S. Geo- of Volcanology, v. 48, no. 1, p. 17-26. logical Survey Professional Paper 525-B, p. B132-B136. Mullineaux, D. R., 1996, Pre-1980 tephra-fall deposits erupted from Deeter, J. D., 1979, Quaternary geology and stratigraphy of Kitsap Mount St. Helens, Washington: U.S. Geological Survey Profes- County, Washington: Western Washington University Master of sional Paper 1563, 99 p. Science thesis, 175 p., 2 plates. Mullineaux, D. R.; Waldron, H. H.; Rubin, Meyer, 1965, Stratigraphy Dethier, D. P.; Pessl, Fred, Jr.; Keuler, R. F.; Balzarini, M. A.; Pevear, and chronology of late interglacial and early Vashon glacial time D. R., 1995, Late Wisconsinan glaciomarine deposition and iso- in the Seattle area, Washington: U.S. Geological Survey Bulletin static rebound, northern Puget Lowland, Washington: Geological 1194-O, 10 p. Society of America Bulletin, v. 107, no. 11, p. 1288-1303. Noble, J. B., 1990, Proposed revision of nomenclature for the Pleisto- Easterbrook, D. J., 1968, Pleistocene stratigraphy of Island County: cene stratigraphy of coastal Pierce County, Washington: Wash- Washington Department of Water Resources Water-Supply Bul- ington Division of Geology and Earth Resources Open File Report letin 25, part 1, 34 p., 1 plate (in 4 parts). 90-4, 54 p. Easterbrook, D. J., 1969, Pleistocene chronology of the Puget Low- Pessl, Fred, Jr.; Dethier, D. P.; Booth, D. B.; Minard, J. P., 1989, Sur- land and San Juan Islands, Washington: Geological Society of ficial geologic map of the Port Townsend 30- by 60-minute quad- America Bulletin, v. 80, no. 11, p. 2273-2286. rangle, Puget Sound region, Washington: U.S. Geological Survey Easterbrook, D.J., 1986, Stratigraphy and chronology of Quaternary Miscellaneous Investigations Series Map I-1198-F, 1 sheet, scale deposits of the Puget Lowland and Olympic Mountains of Wash- 1:100,000, with 13 p. text. ington and the Cascade mountains of Washington and Oregon: Porter, S. C.; Carson, R. J., 1971, Problems of interpreting radiocar- Quaternary Science Reviews, v. 5, p. 145-159. bon dates from dead-ice terrain, with an example from the Puget Easterbrook, D. J., 1994, Chronology of pre-late Wisconsin Pleisto- Lowland of Washington: Quaternary Research, v. 1, no. 3, p. 410- cene sediments in the Puget Lowland, Washington. In Lasmanis, 414. Raymond; Cheney, E. S., convenors, Regional geology of Wash- Porter, S. C.; Swanson, T. W., 1998, Radiocarbon age constraints on ington State: Washington Division of Geology and Earth Re- rates of advance and retreat of the Puget lobe of the Cordilleran ice sources Bulletin 80, p. 191-206. sheet during the last glaciation: Quaternary Research, v. 50, no. 3, Easterbrook, D. J.; Briggs, N. D.; Westgate, J. A.; Gorton, M. P., p. 205-213. 1981, Age of the Salmon Springs glaciation in Washington: Geol- Pringle, P. T., editor; Driedger, C. L.; Frank, D. G.; McKenna, J. M.; ogy, v. 9, no. 2, p. 87-93. Murphy, M. T.; Scott, K. M.; Sisson, T. W.; Vallance, J. W.; and Easterbrook, D. J.; Crandell, D. R.; Leopold, E. B., 1967, Pre-Olym- others, 1994, Mount Rainier, a Decade Volcano GSA field trip. In pia Pleistocene stratigraphy and chronology in the central Puget Swanson, D. A.; Haugerud, R. A., editors, Geologic field trips in Lowland, Washington: Geological Society of America Bulletin, the Pacific Northwest: University of Washington Department of v. 78, no. 1, p. 13-20. Geological Sciences, v. 2, p. 2G-1 - 2G-23. Garling, M. E.; Molenaar, Dee; and others, 1965, Water resources and Rigg, G. B.; Gould, H. R., 1957, Age of Glacier Peak eruption and geology of the Kitsap Peninsula and certain adjacent islands: chronology of post-glacial peat deposits in Washington and sur- Washington Division of Water Resources Water-Supply Bulletin rounding areas: American Journal of Science, v. 255, no. 5, 18, 309 p., 5 plates. p. 341-363. Hansen, B. S.; Easterbrook, D. J., 1974, Stratigraphy and palynology Sceva, J. E., 1957, Geology and ground-water resources of Kitsap of late Quaternary sediments in the Puget Lowland, Washington: County, Washington: U.S. Geological Survey Water-Supply Pa- Geological Society of America Bulletin, v. 85, no. 4, p. 587-602. per 1413, 178 p., 3 plates. LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 23

Shackleton, N. J., 1969, The last interglacial in the marine and terres- Troost, K. G.; Borden, R. K., 1996, New radiocarbon dates from trial records: Proceedings of the Royal Society of London, Series Vashon and Olympia deposits in central Pierce County [abstract]. B—Biological Sciences, v. 174, no. 1034, p. 135-154. In University of Washington Quaternary Research Center, Qua- Smith, Mackey, 1977, Geologic map of the city of Tacoma, Pierce ternary environmental changes in the Pacific Northwest: Univer- County, Washington: Washington Division of Geology and Earth sity of Washington Quaternary Research Center, [1 p., unpaginat- Resources Open File Report 77-9, 1 sheet, scale 1:24,000. ed]. South King County Groundwater Advisory Committee; Economic Waldron, H. H., 1961, Geology of the Poverty Bay quadrangle, Wash- and Engineering Services, Inc.; Hart-Crowser, Inc.; Pacific ington: U.S. Geological Survey Geologic Quadrangle Map GQ- Groundwater Group; Robinson and Noble, Inc., 1991, South King 158, 1 sheet, scale 1:24,000. County groundwater management plan; Grant no. 1, background Walters, K. L.; Kimmel, G. E., 1968, Ground-water occurrence and data collection and management issues: Washington Department stratigraphy of unconsolidated deposits, central Pierce County, of Ecology, 2 v. Washington: Washington Department of Water Resources Water- Troost, K. G., 1999, The Olympia nonglacial interval in the south- Supply Bulletin 22, 428 p., 3 plates. central Puget Lowland, Washington: University of Washington Willis, Bailey, 1898, Drift phenomena of Puget Sound: Geological Master of Science thesis, 123 p. Society of America Bulletin, v. 9, p. 111-162. Troost, K. G.; Booth, D. B.; Sarna-Wojcicki, A. M.; Meyer, C. E.; Winograd, I. J.; Landwehr, J. M.; Ludwig, K. R.; Coplen, T. B.; Riggs, Hagstrum, J. T., 1997, Chronology, mineralogy, and correlation A. C., 1997, Duration and structure of the past four interglaci- of Quaternary tephra and mudflow deposits in the central Puget ations: Quaternary Research, v. 48, no. 2, p. 141-154. Lowland, Washington State [abstract]: Geological Society of Yount, J. C.; Marcus, K. L.; Mozley, P. S., 1980, Radiocarbon-dated America Abstracts with Programs, v. 29, no. 6, p. A-411 - A-412. localities from the Puget Lowland, Washington: U.S. Geological Survey Open-File Report 80-780, 51 p., 1 plate. n Appendix A. Borehole summary

1 Only boreholes used in cross sections and contour maps or that provided a radiocarbon sample are included; 2 State Plane Cooordinates; 3 complete citation for each borehole is given in references following the table; 4 ‘yes’ indicates that samples from that borehole were examined as part of this study.

Borehole1 East2 North2 Ground elev. (ft) Depth (ft) Reference3 Samples4 BA-01 1504004 669307 272.7 235 JRB Associates (1983) no CA-01 1503555 665504 291.5 250 JRB Associates (1983) no CW-06 1507876 662451 301.6 51.5 Enserch (1994) no CW-14 1504381 662970 306.0 276.0 Enserch (1994) yes CW-15 1504574 663982 293.0 266.0 Enserch (1994) yes CW-18 1504919 662559 310.2 363.0 Enserch (1994) yes CW-30 1506425 665308 279.9 280.5 Ebasco (1992) yes CW-31 1504247 664889 296.6 311.0 Ebasco (1992) yes CW-32 1504429 666768 276.9 372.5 Ebasco (1992) yes CW-33 1505229 660076 303.0 288.0 Foster Wheeler (1995) yes CW-34 1505171 658775 311.1 288.0 Foster Wheeler (1995) no DA-01 1502074 657820 299.3 70.0 Ebasco and Shannon & Wilson (1991c) yes DA-02 1502672 659250 300.2 320.0 Ebasco and Shannon & Wilson (1991c) yes DA-04 1500926 658044 283.0 68.5 Ebasco and Shannon & Wilson (1991c) yes DA-07 1500344 660135 281.3 140.0 Ebasco and Shannon & Wilson (1991c) yes DA-08 1499776 659091 275.7 76.0 Ebasco and Shannon & Wilson (1991c) yes DA-11 1498687 660912 271.1 76.5 Ebasco and Shannon & Wilson (1991c) yes DA-12 1497486 660600 273.4 313.0 Ebasco and Shannon & Wilson (1991c) yes DA-12e 1497151 660550 272.0 145.0 Ebasco and Shannon & Wilson (1991c) yes DA-13 1497417 661372 272.3 69.5 Ebasco and Shannon & Wilson (1991c) yes DA-15 1497688 664272 268.5 305.0 Ebasco and Shannon & Wilson (1991c) yes DA-16 1495541 659968 271.8 150.0 Ebasco and Shannon & Wilson (1991c) yes DA-17 1495595 661732 272.5 313.0 Ebasco and Shannon & Wilson (1991c) yes DA-18 1497141 658562 278.7 73.0 Ebasco and Shannon & Wilson (1991c) yes DA-20 1492975 659706 271.8 304.5 Ebasco and Shannon & Wilson (1991c) yes DA-24 1496692 661312 270.1 62.5 Ebasco and Shannon & Wilson (1991c) yes DA-25 1499246 660324 275.2 72.5 Ebasco and Shannon & Wilson (1991c) yes DA-26 1497677 663535 271.4 146.0 Ebasco and Shannon & Wilson (1991c) yes DZ-01 1501278 661521 285.4 108 JRB Associates (1983) no DZ-06 1498243 660491 271.8 63 Greiling and Peshkin (1986) no DZ-09 1499879 660824 271.1 63 Greiling and Peshkin (1985) no DZ-10 1498799 661820 265.9 68 Greiling and Peshkin (1985) no EH-4 1506538 660931 296.8 118 Ebasco and Shannon & Wilson (1991a) yes FZ-01 1509024 662935 279.5 103 JRB Associates (1983) no GC 1501870 659610 280.0 634 Washington Department of Ecology no IH-01 1511307 658675 330.7 103 Ebasco and Shannon & Wilson (1991b) yes IH-03 1509683 659845 326.0 101 Ebasco and Shannon & Wilson (1991b) yes LC-19 1495138 653099 289.2 78.7 Shannon & Wilson (1986) no LC-21 1496426 652743 279.7 150.2 Envirosphere and Shannon & Wilson (1988) yes

24 LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 25

Borehole1 East2 North2 Ground elev. (ft) Depth (ft) Reference3 Samples4 LC-22 1497011 655282 296.1 52.5 Greiling and Peshkin (1985) no LC-26 1497564 651917 276.9 179.0 Ebasco and Shannon & Wilson (1993) yes LC-35 1494905 653530 288.0 219.0 Ebasco and Shannon & Wilson (1993) yes LC-38 1490375 657970 271.0 83.0 Shannon & Wilson (1986) yes LC-40 1490263 656927 277.3 179.0 Ebasco and Shannon & Wilson (1994) yes LC-41 1491859 655154 281.8 302.0 Envirosphere and Shannon & Wilson (1988) yes LC-44 1493259 656849 271.2 149.8 Envirosphere and Shannon & Wilson (1988) yes LC-47 1493403 655176 280.6 269.0 Ebasco and Shannon & Wilson (1993) yes LC-50 1495547 652150 271.7 208.0 Ebasco and Shannon & Wilson (1993) yes LC-55 1497114 653766 289.6 300.0 Envirosphere and Shannon & Wilson (1988) yes LC-60 1489536 658736 276.3 73.0 Envirosphere and Shannon & Wilson (1988) yes LC-61 1489769 659151 277.2 80.0 Envirosphere and Shannon & Wilson (1988) yes LC-64 1496580 652424 276.5 79.0 Envirosphere and Shannon & Wilson (1988) yes LC-65 1494223 654393 286.5 80.0 Envirosphere and Shannon & Wilson (1988) yes LC-66 1492176 656900 281.2 189.0 Ebasco and Shannon & Wilson (1994) yes LC-67 1490344 655739 263.7 179.0 Ebasco and Shannon & Wilson (1993) yes LC-68 1492566 653737 281.0 259.0 Ebasco and Shannon & Wilson (1993) yes LC-69 1491985 655128 282.2 205.0 Ebasco and Shannon & Wilson (1993) yes LC-70 1491765 655182 280.7 219.0 Ebasco and Shannon & Wilson (1993) yes LC-71 1489355 657746 269.5 230.0 Ebasco and Shannon & Wilson (1994) yes LC-72 1488749 656736 263.9 194.0 Ebasco and Shannon & Wilson (1994) yes LC-73 1488280 656095 269.6 230.0 Ebasco and Shannon & Wilson (1994) yes LF4-MW1 1478994 655689 255.6 166.5 Applied Geotechnology (1993) no LF4-MW3 1478313 656247 241.0 166.5 Applied Geotechnology (1993) no LF4-MW4 1477961 656547 245.8 336.5 Applied Geotechnology (1993) no LF4-MW6 1477333 656287 223.2 165.0 Applied Geotechnology (1993) no LF4-MW12B 1477005 658234 236.0 208 Applied Geotechnology (1993) no LF4-MW16 1475180 657238 232.6 306.0 Applied Geotechnology (1993) no LT-09 1507958 661401 311.7 189.0 Enserch (1994) no LZ-04 1496741 657756 277.4 302.0 Ebasco and Shannon & Wilson (1991c) yes O’Neil & Martin 1494040 658208 278.0 320.0 Washington Department of Ecology no Poe & McGuire 1493712 660200 265.0 222.0 Washington Department of Ecology no RD-1 1489009 655799 272.3 206.9 U.S. Army Corps of Engineers (1982) no RD-2 1490076 654908 274.5 140.5 U.S. Army Corps of Engineers (1982) no T-01 1490023 660701 272.5 79.0 Ecology and Environment (1986) no T-02 1489711 660410 272.8 80.0 Ecology and Environment (1986) no T-09 1490036 660709 272.1 310.0 Envirosphere and Shannon & Wilson (1988) yes T-10 1489689 660316 270.5 118.0 Ecology and Environment (1986) no T-11 1489736 661502 277.0 80.0 Envirosphere and Shannon & Wilson (1988) yes T-12 1490605 660206 274.4 70.0 Envirosphere and Shannon & Wilson (1988) yes TZ-01 1495090 659956 272.7 73.0 Greiling and Peshkin (1985) no TZ-02 1495903 660395 264.7 68 Greiling and Peshkin (1985) no W1 1497905 660451 269.8 120 Ecology and Environment (1984) no W2 1497878 660136 268.2 77 Ecology and Environment (1984) no W3 1497130 660406 269.3 88 Ecology and Environment (1984) no 26 REPORT OF INVESTIGATIONS 33

Borehole1 East2 North2 Ground elev. (ft) Depth (ft) Reference3 Samples4 W4 1497137 659961 266.2 122 Ecology and Environment (1984) no 88-1-SS 1471543 657079 220.0 215.8 Woodward-Clyde Consultants (1989) no 88-5-SS 1468231 658349 215.0 191 Woodward-Clyde Consultants (1989) no 90-PM-1 1483260 662620 250.5 140 Shannon & Wilson (1990) yes Well 5001 1497420 661820 280.0 435 Washington Department of Ecology no Well 4/6 Comp 1489500 653500 270.0 295 Noble (1990) no Well 8 1493920 653680 287.0 1008.0 Washington Department of Ecology no

BOREHOLE LOG REFERENCES Applied Geotechnology, Inc., 1993, Final remedial investigation re- Greiling, R. W.; Peshkin, R. L., 1985, Installation restoration pro- port; Volume I, Landfill 4 and solvent refined coal pilot plant, Fort gram, Phase II—Confirmation/quantification, stage 1; Final re- Lewis, Washington: Applied Geotechnology, Inc. [under contract port for American Lake garden tract, Washington: Science Appli- to] U.S. Army Corps of Engineers Seattle District, 1 v. cations International Corporation [under contract to] U.S. Air Ebasco Environmental1; Shannon & Wilson, Inc., 1991a, Draft—Site Force Occupational and Environmental Health Laboratory, investigation report; McChord Air Force Base, area E, site investi- 1064 p. gation: Ebasco Environmental [under contract to] U.S. Army Greiling, R. W.; Peshkin, R. L., 1986, Installation restoration pro- Corps of Engineers Seattle District, 1 v. gram, Phase II—Confirmation/quantification, stage 2; Final re- Ebasco Environmental1; Shannon & Wilson, Inc., 1991b, Draft—Site port for McChord Air Force Base, Washington: : Science Applica- investigation report; McChord Air Force Base, area I, site investi- tions International Corporation [under contract to] U.S. Air Force gation: Ebasco Environmental [under contract to] U.S. Army Occupational and Environmental Health Laboratory, 493 p. Corps of Engineers Seattle District, 1 v. JRB Associates, 1983, Geohydrologic evaluation and chemical inves- Ebasco Environmental1; Shannon & Wilson, Inc., 1991c, Final reme- tigations for McChord Air Force Base, Washington—Report of dial investigation report—McChord Air Force Base, area the reconnaissance survey performed under the Phase IIb installa- D/American Lake garden tract, remedial investigation/feasibility tion restoration program: JRB Associates [under contract to] U. S. study: Ebasco Environmental [under contract to] U.S. Army Air Force Occupational and Environmental Health Laboratory, Corps of Engineers Seattle District, 1 v. 1v. Ebasco Environmental1; Shannon & Wilson, Inc., 1993, Technical Noble, J. B., 1990, Proposed revision of nomenclature for the Pleisto- memorandum—Fort Lewis Logistics Center lower aquifer cene stratigraphy of coastal Pierce County, Washington: Wash- groundwater study; Final: Ebasco Environmental [under con- ington Division of Geology and Earth Resources Open File Report tract to] U.S. Army Corps of Engineers Seattle District, 1 v. 90-4, 54 p. Ebasco Environmental1; Shannon & Wilson, Inc., 1994, Fort Lewis Shannon & Wilson, Inc., 1986, Source areas, occurrence and recom- Logistics Center, lower aquifer study; Final addendum to final mended remedial alternatives for trichloroethylene in groundwa- technical memorandum: Ebasco Environmental [under contract ter, Fort Lewis Logistics Center, Fort Lewis, Washington: Shan- to] U.S. Army Corps of Engineers Seattle District, 1 v. non & Wilson, Inc. [under contract to] U.S. Army Corps of Engi- neers Seattle District, 1 v. Ebasco Services Incorporated1, 1992, Final remedial investigation report, McChord Air Force Base washrack/treatment area RI/FS, Shannon & Wilson, Inc., 1990, Final site investigation report, Park Tacoma, Washington: Martin Marietta Energy Systems, Inc. [un- Marsh landfill, Fort Lewis, Washington: Shannon & Wilson, Inc. der contract to] U.S. Department of Energy, 1 v. [under contract to] U.S. Army Corps of Engineers Seattle District, 1v. Ecology and Environment, Inc., 1984, Field investigation of groundwater at American Lake gardens tract, Tacoma, Washington: U.S. Army Corps of Engineers, 1982, Madigan Army Medical Center, Ecology and Environment, Inc. [under contract to] U.S. Environ- Ft. Lewis, Washington—Geotechnical report: U.S. Army Corps mental Protection Agency, 1 v. of Engineers [Seattle, Wash.], 1 v. Ecology and Environment, Inc., 1986, Tillicum municipal well inves- Woodward-Clyde Consultants, 1989, Fort Lewis landfill no. 5, reme- tigation, Tillicum, Washington: Ecology and Environment, Inc. dial investigation/feasibility study—Hydrogeology technical [under contract to] U.S. Environmental Protection Agency, 1 v. memorandum; Draft: Woodward-Clyde Consultants [under contract to] U.S. Army Corps of Engineers Seattle District, 1 v. Enserch Environmental1, 1994, Draft final CY 1993 annual report— Long-term monitoring program, McChord Air Force Base: Martin Washington Department of Ecology, boring log and well completion Marietta Energy Systems, Inc. [under contract to] U.S. Depart- records. ment of the Air Force, 1 v. Envirosphere Company1; Shannon & Wilson, Inc., 1988, Final remedial investigation report—Fort Lewis Logistics Center, remedial investigation/feasibility study: Envirosphere Company [under contract to] U.S. Army Corps of Engineers Seattle District, 1 v. Foster Wheeler Environmental Corporation, 1995, Final CY 1994 annual report—Long-term monitoring program, McChord Air Force 1 Ebasco Environmental, Ebasco Services Incorporated, Enserch Envi- Base: Martin Marietta Energy Systems, Inc. [under contract to] ronmental, and Envirosphere Company are now Foster Wheeler Envi- U.S. Department of the Air Force, 1 v. ronmental Corporation. Appendix B. Boreholes with radiocarbon data

The original published logs for these boreholes are reproduced on the following pages (Figs. B-1 through B-4). See Appendix A for complete borehole log references. BGS, below ground surface; MSL, above mean sea level.

Borehole DA-2c,d Borehole 4/6 Composite (Ebasco and Shannon & Wilson, 1991c) (Noble, 1990) See Figure B-1 for original published log See Figure B-3 for original published log

Radiocarbon date: Radiocarbon date:

96 ft BGS >40,000 yr B.P. (I-15,705) 60 ft BGS 25,100 ±600 yr B.P. (I-15,437)

Inferred stratigraphic units: Inferred stratigraphic units:

0–40ftBGS Vashon recessional outwash 217 – 270 ft MSL Vashon Drift 40–45ftBGS Vashon till 195 – 217 ft MSL Olympia nonglacial sediments 45–75ftBGS Vashon advance outwash 163 – 195 ft MSL Pre-Olympia drift 75–85ftBGS Vashon glaciolacustrine sediments 119 – 163 ft MSL Second nonglacial deposits 85 – 121 ft BGS Pre-Olympia drift -22 – 119 ft MSL Third glacial drift 121 – 320 ft BGS Third glacial drift -25 – -22 ft MSL Third nonglacial deposits

Borehole DA-12e Borehole LF4-MW12B (Ebasco and Shannon & Wilson, 1991c) (Applied Geotechnology, 1993) See Figure B-2 for original published log See Figure B-4 for original published log

Modifications to geologic log (based upon re-examination of Radiocarbon date: archived borehole samples): 60 ft BGS 13,630 ±90 yr B.P. (Beta-52222) 5–15ftBGS dense gray silty sandy gravel (till) 15–25ftBGS brown-gray slightly silty to silty sandy gravel Inferred stratigraphic units: 25–35ftBGS dense gray silty sandy gravel (till) 0–58ftBGS Vashon Drift 65–74ftBGS gray silty fine sand; wet 58 – 101 ft BGS Vashon glaciolacustrine sediments 101 – 134 ft BGS Pre-Olympia drift Radiocarbon dates: 134 – 153 ft BGS Second nonglacial deposits 92 ft BGS 13,510 ±80 yr B.P. (Beta-79885) 153 – 208 ft BGS Third glacial drift 140 ft BGS >41,300 yr B.P. (Beta-81801)

Inferred stratigraphic units:

0–35ftBGS Interbedded Vashon till and outwash 35–74ftBGS Vashon outwash 74–98ftBGS Vashon glaciolacustrine sediments 98 – 145 ft BGS Pre-Olympia drift

27 28 REPORT OF INVESTIGATIONS 33

GEOLOGIC LOG ii GAMMA LOG .z= Increasing Radiation - i- (Seconds/250 Emissions) Ground Elevation: 300.2 Feet 0 40 30 20 10 0 ordand Brown, slightly silty, sandy GRAVEL and Cement COBBLES; moist; (Fill to 3.5'); GP Qvs ' Brownish-gray, silty, sandy GRAVEL with 20 ...... : ...... : .. . . ' scattered cobbles; wet; (Ablation Till?); GP-GM C ' Grayish-brown, silty, sandy GRAVEL with av sz. d ,' 2" ID Sch abundant cobbles; moist to wet; GP-GM Sl. , 80 PVC 40 Gray, silty sandy GRAVEL; wet; (Ablation ' Till?l· GM ' ' ' 60 ' ' Brownish-gray, sandy GRAVEL with cobbles; wet· GP ' ray, fine sandy SILT to clayey SILT with ml 80 ' slightly silty, fine to medium SAND interbeds; ' dilatant· wet· ML ' ' Bentonite Gray to purplish-graY., fine to medium SAND Seal with trace of silt to silty interbeds; wood fragments and chunks ; wet; SP/SP-SM; No. 8 to 12 gravelly at 90', 103' and 120' Colorado Sand Filter

Pea Gravel 140 asst

154

Dark greenish-gray, sandy GRAVEL; wet; ass GP Centralizer 180 ------'-182 . No. 20 Slot 188 PVC Screen ass 200 asst

ass 220 225 230 Gray, slighdy fine sandy, clayey SILT with scattered gravel; occasional wry fine sand 240 laminae; moist; ML Qpy?

260 From 265 to 275 feet: gray SILT with occasional gravel; moist; ML From 275 to 300 feet: gray SILT to 280 fine sandy SILT; moist;~L Slightly clayey below 300' . . 300 ...... ,...... ,...... Grades to clayey SILT by 320'

1--....;;;eo__n_o_M.;.;,,.;;O_F.;;B.;;O..;.R;;.;.IN.;.;G;;..3;;..;20;.;..;.F.;;E:ET.;.... __ ___.-320 __...._ __..;.3.;;_20...... _r-- ______... 3;;..;20:.;..i.._._ ...... 1.- ____. McChord AFB, Area D and ALGT Drilled By: Holt Drilling NOTES Pierce County, Washington Drilling Method: Cable Tool 1. Soil descriptions from O to 71 Sampling Method: Split Spoon & Cuttings feet based on samples obtained Completion Date : 4-12-89 in DA-2a,b. MONITORING WELLS DA-2c,d 2. The contacts represent the approx. boundaries between soil June 1989 T-1070-07 types and the actual transitions may be gradual. SHANNON & WILSON, INC. Geotechnical Consultants FIG. A·3

Figure B-1. Borehole DA-2c,d (Ebasco and Shannon & Wilson, 1991c) LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 29

GAMMA LOG GEOLOGIC LOG u:: .Sl u:: AS-BUILT £ £ Increasing Radiation - Locking E .-CDis- 15.. Ill> (Seconds/250 Emissions) t--8"--i Steel Ground Elevation: 272.0 Feet CD S·'e 2- Monument 0 (!)::::, 3:j 0 40 30 20 10 ~ H~ 0 2 r--...Cement Gray, silty, fine gravelly SAND; moist to wet; SM Bentonite ,Seal . .. .. 10 ...... , ...... 10.0 I e - Natural Backfill Sl. 20 ...... ,· ,.. ~ Qv '? ~ 30 ...... , ...... ,...... 32- ~ Gray, slighdy silty, gravelly SAND; wet; SP-SM ~' ' , . . ,', ~, ----- 40 ...... ,', ' ' 42- , ' , ' : ' , ' ' , ' Gray, fine gravelly SAND with trace of silt; wet; ' , ' ' , ' ' , ' , SP ' ' ' Bentonite .... . 50 ...... , ...... ' , ' !', ' ' , ' ' Slurry ' , ' << 56- ' , ' ' , ' . . ' , ' I', ' Gray, sandy GRAVEL with cobbles; wet; GP .... . 60 ...... ' , ' ' , ' ' , ' ' , ' ' ' ' , ' Gray, silty, fine, gravelly SAND; wet; SM ~~- ,',, ' , ' "\. r ...... ' , ' ' , ' 70 ' , ' ' , ' , , Gray, clayey SILT; scattered medium to coarse ' , ' ' ' sand; trace of organics; moist; ML : ' ' ' , ' . . ' , ' ' , ' . .... 80 ...... ' , ' ' , ' ' , ' ' , ' 2" ID Sch ' , ' ' ' 40PVC ,',' ' ~~ ' ' , ' ..... 90 ...... ,',, , ' , ' ' , ' ' , ' ' , ' .:t: ' , ' ' , ' 98 - 0 ' , ' ' , ' ···· · Cl) 100 ...... ,...... -0 ' , ' ' , ' Gray to brownishfa~ silty to trace of silt, fine Q. ' , ' ' , ' to fine to medium A D; wet; SM/SP ' , ' ' , ' 6 : ' , ' ' , ' !!? . ' . .... Q. 110 ...... ' , ' ' , ' - scattered gravel below 131 feet ' ' ' ' 113.5 Centralizer . .: 119.0 · -·-· 120 ...... 120.0 V No. 20Slot I ~ PVC 123.0 . '--- Screen I:;- P...... - No. 8 to 12 130 ··- · · -· -· · · -···· · ····· · · ·· ·. · =· ., Colorado 133.0 : ·: ~( : r--..Sand Filter 135- Th,e•dod Gray, fine, sandy SILT; massive; moist; ML ' 136.0.,PVC Cao ..... 140 ----·-· · ··--· ·· · ···. · ·· ·· -- 145- 145.0 BOTIOM OF BORING 145 FEET . .... 150 ...... ' ......

160 McChord AFB, Area D and ALGT Drilled By: Holt Drilling Pierce County, Washington Drilling Method: Cable Tool Sampling Method: Split Spoon & Cuttings Completion Date: 10-18-89 NOTE MONITORING WELL DA-12e The contacts represent the approx. boundaries between June 1989 T-1070-07 soil types and the actual transitions may be gradual. SHANNON & WILSON, INC. Geotechnical Consultants I FIG. A-16

Figure B-2. Borehole DA-12e (Ebasco and Shannon & Wilson, 1991c) 30 REPORT OF INVESTIGATIONS 33

BASIC DATA LOG R-2

Composite Logs for Wells 4 and 6, New Madigan Hospital (19/2E-28H) Wells are 1,200 feet apart, altitude at surface is 270 feet.

Altitude of base (ft) Thickness (ft) Vashon Drift, Steilacoom Gravel Member 230 Brown-gray cobbly gravel (to 10-in. diameter) with some sand and 40 silt. Discovery nonglacial unit 217 Brown medium sand, silty; some gravel;some thin silt layers. 13 203 Brown sandy, silty gravel, with cobbles to 10-in. diameter and embed- 14 ded wood and peat. Has mudflow texture. Mt. Rainier clast types pre- dominant. Wood radiocarbon dated at 25,100 +/- 600 yr (D. K. Balmer, oral commun., 1989). 195 Brown, fine to medium, silty sand. 8 Narrows glacial unit 186 Red-brown sand. 9 177 Brown sand-gravel diamicton (till?). 9 168 Brown, small gravel and coarse sand. 9 163 Brown, sandy, silty gravel. 5 Kitsap Formation 126 Brown, silty sand, silty clay, some gravel. Laminations noted. 37 119 Brown silt and sand with ash partings. 7 67 Brown, iron-stained and iron-cemented sand and gravel with wood 52 pieces. Flett Creek glacial unit 63 Gray gravel, sand, silt, clay (till). 4 40 Gray silt, sandy, clayey gravel with boulders. 23 14 Brown and gray (layered) silty sand and gravel. 26 3 As in overlying interval, but with notable coal detritus. 11 -20 “Clean” well-sorted sand and gravel with notable coal detritus. 23 -22 Brown gravelly coarse sand. 2 Clover Park nonglacial unit(?) -25 Brown, fine to medium sand. 3 (Base not penetrated.)

Figure B-3. Borehole 4/6 Composite (Noble, 1990) LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 31

FIELD MEASUREMENTS

0 Gas MONITORING WELL GROUNDWATER 0 u. Water Quality Concentration CONSTRUCTION OBSERVATIONS .;., .; DETAILS ::::. ., a. 0 .c ::, Static Drilling Water- ci. ..:t. "O a. ..J ii E C E w ~E Water Water Bearing ., 0 :r 0 ., ..J > a. 0 - a' 0.9: Level Level Zone 0 2.0' BROWN SANDY GRAVEL (GP) very 3.0' dense, moist; with some to a trace of silt, and some cobbles. ND ND

10 50/0.3' ND ND

NO ND

20 Note oxidized iron staining. 92/0.9' ND NO

ND ND GRAY SILTY GRAVEL (GM) very 30.0' 30 dense, wet; with some sand. ND ND GRAY GRAVEL (GP) very dense, saturated; coarse grained, with 50/0.25' some sand. ND ND

40 50/0.4' ND ND Becomes sandy, medium dense, fine grained. 22 ND ND GRAY GRAVELLY SAND (SP) very 50 dense, saturated; medium to 50/0.3' coarse grained. ND ND Becomes very dense, with some fine gravel. 75/0.5 ' NO ND GRAY SILT (ML) very stiff, moist; with 60 interlayers of Brown Peat (PT). 50/0.4' ND ND GRAY SAND (SP) medium dense, saturated; medium grained, with a 20 trace of fine gravel. Note interbeds ND ND of Gray Silt (ML). 70 20 ND ND

26 ND ND GRAY SILT (ML) hard, moist. Note 80 infrequent thin interbeds of sand 50/0.5' from 80' to 95'. ND ND

95/0.75 ND ND

90 50/0.3' ND ND

85/0.8' ND NO 100

Equipment Bucyrus-Erie 22-W Date 1/15/92 land Surface Datum______Elevation 236.0 feet Source ------NGVD 1929

Figure B-4. Borehole LF4-MW12B (Applied Geotechnology, 1993) 32 REPORT OF INVESTIGATIONS 33

FIELD MEASUREMENTS

MONITORING WELL GROUNDWATER Gas CONSTRUCTION Water Quality Concentration OBSERVATIONS .; ;;; DETAILS ... Q. ... u::, = a. .. "C Q. Static Drilling Water ~ E 0 C E Water Water Bearing :r: 0 Cl) .. GEOLOGIC LOG Q. (.) en iii I- Level Level Zone --=- ND ND BROWN GRAVELLY SAND (SP) very dense, saturated; coarse grained, with a trace of silt. 50/0.3' 7.92 310 10.1 ND ND

50/0.4' 7.72 270 11.2 ND ND BROWN SILTY GRAVEL (GM) very I dense, wet; with some medium sand. 93/0.9' ND ND

120 85/0.7' 7.41 290 10.6 ND ND

50/0' 7.55 290 10.7 ND ND

BROWN SAND (SP) dense, satu- 130 rated; fine to medium grained, with 40 ND ND a trace of gravel.

GRAY SILT (ML) hard moist. Note 50/0.4' ND ND thin interbeds of Dark Brown Peat (PT), lavender hue, mottling. '. 140 50/0.1" ND ND

75/0.5' ND ND

150 ND ND

GRAY SILTY GRAVEL (GM) very 50/0.3' dense, wet; with some sand. ND ND

160 50/0.4' ND ND

50/0.4' ND ND GRAY SANDY GRAVEL (GP) very 172.2' 170 dense, saturated; with a trace of 50/0.4' silt. ND ND BROWN SILTY GRAVEL (GM) dense, wet; with some sand. Note 50/0.4' oxidized iron staining. 7 .4 170 9.0 ND ND 178.2' BROWN SANDY GRAVEL (GP) very 180 dense, saturated; with a trace of 181 .2' 25/0.1' silt. Note oxidiud iron staining. 6.96 150 8.7 ND ND ...... BROWN SILTY GRAVEL (GM) very 184.5' dense, wet. 80/0.9' ND ND 188.0· GRAY SANDY GRAVEL (GP) very dense, saturated; with a trace of silt. ND ND 193· Note cobbles in bailer return at 190'. 195.5' 1----1 BROWN SILTY GRAVEL (GM) very ND ND 198' dense, wet; with some sand.

Figure B-4. Borehole LF4-MW12B (Applied Geotechnology, 1993) (continued) LATE PLEISTOCENE STRATIGRAPHY IN THE PUGET LOWLAND, WASHINGTON 33

FIELD MEASUREMENTS

MONITORING WELL GROUNDWATER o Gas CONSTRUCTION z- ~ Water Quality Concentration OBSERVAllONS ;;; DETAILS "' a. ~ u:, .t: a."' "Cl a. -' Static Drilling Water- "'3: C: UJ E 0 E ::EE Water Water Bearing a :x: 0 -' > a. 0"' en GEOLOGIC LOG i'ii a. u ...."' ii 0 .s Level Level Zone "' 201.0' 200 NO NO 202.0' BROWN SANDY GRAVEL (GP) 203.0' saturated. ---'----~~, BROWN SILTY GRAVEL (GM) wet. 90/0.8' ND NO BROWN SANDY GRAVEL (GP) very 208.0' dense. saturated; with a trace of 210 silt.

220

230

240

250

260

270

280

290

300 Applied Geotechnology Inc. Summary Log of LF4-MW128 PlATE Geological Engineering Geology & Hydrogeology landfill 4/SRCPP RI Fort Lewis, Washington F23

JOB NUMBER DRAWN APPROVED DATE REVISED o.:.TE 14,340.100 SES Ao:_ \ \ 14/5'3

Figure B-4. Borehole LF4-MW12B (Applied Geotechnology, 1993) (continued)