SCALE 1: 24 000

1 0 1 MILE 1/ 2

1 .5 0 1 KILOMETER

CONTOUR INTERVAL 40 FEET

NATIONAL GEODETIC DATUM OF 1929

QUADRANGLE LOCATION

WASHINGTON

TRUE NORTH

APPROXIMATE MEAN

DECLINATION, 1995

21°

MAGNETIC NORTH

ev. 1973)

one 10

GEOLOGIC SUMMARY

INTRODUCTION

The Wildcat Lake quadrangle lies in the forearc of the Cascadia subduction zone, about

20-km east of the Cascadia accretionary complex exposed in the Olympic Mountains (Taborand Cady, 1978), and about 100-km west of the axis of the Cascades volcanic arc. Thequadrangle lies near the middle of the Puget Lowland, which typically has elevations less than600 feet (183 m), but on Gold Mountain, in the center of the quadrangle, the elevation risesto 1761 feet (537 m). This anomalously high topography also provides a glimpse of the deepercrust beneath the Lowland. Exposed on Green and Gold Mountains are rocks related to theCoast Range basalt terrane. This terrane consists of Eocene submarine and subaerial tholeiiticbasalt of the Crescent Formation,which probably accreted to the continental margin in Eocenetime (Snavely and others, 1968). The Coast Range basalt terrane may have originated as anoceanic plateau or by oblique marginal rifting (Babcock and others, 1992), but its subsequentemplacement history is complex (Wells and others, 1984). In southern Oregon, onlappingstrata constrain the suturing to have occured by 50 Ma; but on southern Vancouver Islandwhere the terrane-bounding Leech River fault is exposed, Brandon and Vance (1992) concludedsuturing to North America occurred in the broad interval between 42 and 24 Ma. Afteremplacement of the Coast Range basalt terrane, the Cascadia accretionary complex, exposedin the Olympic Mountains west of the quadrangle, developed by frontal accretion and underplating(e.g. Clowes and others, 1987). The Seattle basin, part of which lies to the north of GreenMountain, also began to develop in late Eocene time due to forced flexural subsidence alongthe Seattle fault zone (Johnson and others, 1994). Domal uplift of the accretionary complexbeneath the Olympic Mountains occurred after ~18 million years ago (Brandon and others,1998). Ice-sheet glaciation during Quaternary time reshaped the topography of the quadrangle,and approximately two-thirds of the map area is covered with Quaternary deposits related tothe last glaciation. Geophysical studies and regional mapping indicate the Seattle fault liesnorth of Green Mountain. This fault produced a large earthquake about 1000 years ago andmay pose a significant earthquake hazard (Bucknam and others, 1992; Atwater and Moore,1992; Karlin and Abella, 1992; Schuster and others, 1992; Jacoby and others, 1992). Wefound no evidence of Holocene faulting in the Wildcat Lake quadrangle.

Geologic mapping within and marginal to the quadrangle began with Willis (1898), who

described glacial deposits in Puget Sound. Weaver (1937) correlated volcanic rocks in thequadrangle to the Eocene Metchosin Volcanics on Vancouver Island. Sceva (1957), Garlingand Moleenar (1965), and Deeter (1978) all focussed on mapping and understanding theQuaternary stratigraphy of the Kitsap Peninsula, but they also examined bedrock in thequadrangle. Reeve (1979) was the first to examine the igneous rocks on Green and GoldMountains in some detail, and Clark (1989) significantly improved Reeve’s (1979) mapping.Clark’s (1989) mapping was conducted soon after extensive logging on the mountains. Asurficial geologic map of the Seattle 1:100,000-scale quadrangle, which includes the WildcatLake 1:24,000-scale quadrangle, was published by Yount and others (1993). Yount and Gower(1991) also published a bedrock geologic map of the Seattle quadrangle. Geologic mappingfor this report was conducted by Haeussler in the spring and summer of 1998 and in thewinter of 1999. We could not substantially improve upon the bedrock mapping of Clark (1989)and thus it is incorporated into this map. Well data in the southeastern corner of the map areaalso helped to constrain the surficial mapping (Geomatrix Consultants, 1997). In addition,1995 vintage 1:12,000-scale aerial photographs were also used in mapping Quaternarydeposits. Geologic time scale is that of Berggeren and others (1995).

STRATIGRAPHY

Tertiary Bedrock

Lithologic similarity, similar chemistry, similarity in age, and proximity lead us to assign

the volcanic and volcaniclastic rocks at Green and Gold Mountains to the Crescent Formationexposed on the Olympic Peninsula to the northwest, west, and southwest (Arnold, 1906;Tabor and Cady, 1978). Clark (1989) compared subaerial volcanic rocks of the CrescentFormation on Green and Gold Mountains (unit Tcb) to the lower and upper Crescent Formationon the Olympic Peninsula. The average subaerial flow thickness (9 m) at Green and GoldMountains is thinner than flows in the Crescent Formation elsewhere (flow thicknesses of 30-50 m), and the size of vesicles (7 cm) is much larger than the largest vesicles in the CrescentFormation elsewhere (<4 cm). Nonetheless, Clark (1989) concluded the differences could beexplained by proximity of the Green and Gold Mountains rocks to the volcanic source, whereasthe others were distal. In addition, both rock units are subalkaline and tholeiitic, both haveminor and trace elements that plot in the same fields on discriminant diagrams.

There are seven radiometric ages from the igneous rocks on Green and Gold Mountains.

Duncan (1982) analyzed samples from three basalt flows along the northwestern shore ofSinclair Inlet, southeast of Bremerton, and east of the Wildcat Lake quadrangle. Whole rockK-Ar ages were between 43.3 and 49.2 Ma. Two of the samples were reanalyzed with the

40Ar/39Ar method, and yielded whole-rock total-fusion ages of 51.7

±2.4 and 55.3

±3.1 Ma.

Duncan (1982) also step heated a whole-rock split and interpreted a 55.4

±3.2 Ma age. Clark

(1989) obtained, through Duncan, two 40Ar/39Ar total-fusion dates on one sample of

leucogabbro. The ages were 50.4

±0.6 Ma and 49.2

±0.8 Ma. We obtained a 206Pb/238U age

of 50.5

±0.6 Ma from leucogabbro at the base of Green Mountain (Haeussler and others, 2000).

At localities northwest of the quadrangle, basaltic submarine deposits of the Crescent

Formation have Ulatisian-age foraminifera (Yount and Gower, 1991). No ages were obtainedfrom the subaerial basalts, but the overlying Aldwell Formation has benthic foraminifera andmollusks with ages from upper Ulatisian to lower Narizian (Spencer, 1984). Therefore, thesesubaerial Crescent Formation basalts have ages around 46-50 Ma on the time scale of Berggrenand others (1995). By correlation, it is likely the Crescent Formation basalt flows in the WildcatLake quadrangle are of the same age. The fact that the 40Ar/39Ar dates on the basalt flows

analyzed by Duncan (1982) were slightly older could be explained by: 1) recoil effects, becausethe 40Ar/39Ar analyses were whole rock, 2) the Crescent Formation basalts may be slightly

time transgressive, or 3) the Crescent Formation basalts are lower Ulatisian rather than upperUlatisian. The geochemical signature of the basalts and leucogabbro on Green and GoldMountains indicates they are related. Therefore, because the 40Ar/39Ar ages are older thanthe 206Pb/238U age, we infer the 40Ar/39Ar ages probably suffer from excess argon or recoil.

The rock column exposed on Green and Gold Mountains, referred to as the ‘Bremerton

rocks’ by Clark (1989), is somewhat like that of an ophiolite with basal gabbro beneath a locallysheeted dike complex, beneath submarine basalts and volcaniclastic rocks, beneath subaerialbasalt flows. Clark (1989) found more than 60 m of basal leucogabbro and pegmatoid (unitTeg). Numerous diabase and basaltic dikes intrude the upper part of this unit and mapped itseparately (unit Tegd). The overlying sheeted dike complex is approximately 150-m thick andconsists entirely of dikes of diabase and basalt. The submarine volcanic unit (Tcbs) consists ofbasalt flows interbedded with basaltic sandstone, siltstone, tuffs, and basaltic breccia. Overlyingthe submarine volcanic unit are subaerial basalt flows (unit Tcb) more than 180-m thick. Traceelement data from intrusive and extrusive rocks are similar, suggesting they are related (Clark,1989). The pseudostratigraphy differs from an idealized ophiolite stratigraphy in severalimportant ways (Clark, 1989): 1) It lacks a basal ultramafic complex, 2) the Green and GoldMountain dike complex has a thickness of about 150 m, in contrast to more than a kilometerof sheeted dikes in typical oceanic crust, 3) the dikes are locally, but not ubiquitously, sheeted,and 4) the Green and Gold Mountain sequence is capped by subaerial basalt, whereas mostophiolites are overlain by deep marine sediments. Clark (1989) found that the geochemistryof the gabbro and basalts is transitional between normal mid-ocean ridge basalt (MORB) andenriched oceanic island basalt. Preliminary modeling of aeromagnetic and gravity data overGreen and Gold Mountains (Haeussler and others, 2000) indicate there are highly magnetic,dense rocks within a few kilometers of the surface, beneath Green an Gold Mountains.Therefore, there probably is a basal ultramafic complex. Despite the differences between theGreen and Gold Mountains rocks and ophiolites, the presence of the dike section on Greenand Gold Mountains and the overall pseudostratigraphy of an ophiolite indicate that theserocks formed in an extensional environment.

Andesite dikes are the youngest bedrock unit (blue dike symbol on map). These dikes cut

all other rock units, and Clark (1989) reported geochemical data from one sample. I t h a sextremely low Ti, low P, high Zr relative to Nb, and very low Cr, which are consistent with ahigh degree of partial melting. Clark (1989) concluded, based on this chemistry and crosscuttingrelations that the dikes are not related to the other rock types on Green and Gold Mountains.

Surficial Deposits

Overlying the Tertiary bedrock are unconsolidated deposits related to the last glaciation—

the Vashon stade of the Fraser glaciation of Armstrong and others (1965). The Vashon icesheet first covered the study area around 17,400 yr B.P., reached its maximum extent insouthern Puget Sound around 16,950 yr B.P. (Porter and Swanson, 1998), and covered theregion with up to 1500 m of ice (Booth, 1987). As the ice sheet advanced south of PortTownsend, it blocked northward drainage from the Puget Sound region and formed proglaciallakes that drained southward into the Chehalis River and then to the Pacific Ocean. There areno outcrops of the sediments deposited in these laces within the quadrangle, even among thelowest exposures along Big Beef and Stavis Creeks. However, clay was encountered in boreholesat the Olympic View Sanitary Landfill, south of Barney White Ranch along the southeasternedge of the quadrangle, which we infer was deposited as proglacial lake sediments. This claylies approximately at sea level and is overlain by sandy and gravelly advance outwash (unit Qva)deposited by streams and rivers issuing from the front of the advancing ice sheet. Excellentexposures of advance outwash can be seen along a road leading down to Big Beef Creeknorthwest of Wildcat Lake. A couple meters above the level of the creek, there is a foresettopset transition. Further up the section, sand and gravel was deposited as debris flows, withpoor to no sorting, but there is a weak alignment of clasts. The percentage of cobbles in thedebris flows appears to generally increase up section. Till (unit Qvt) marks the presence of theice sheet in the study area, and mantles most upland surfaces. Till was found on Green Mountainat elevations up to 1350 feet (410 m). Ice overrode both Green and Gold Mountains, roundingthe mountaintops. Green and Gold Mountains deflected the ice sheet as it found the easiestway over the mountains. Linear features in the till plane north of the mountains trend southwest,whereas those south of the mountains trend south-southwest. Granitic clasts within the tillattest to a source at least 150km away in the Coast Mountains of British Columbia.

The Puget lobe rapidly retreated from its maximum extent, leaving the Wildcat Lake

quadrangle ice free by about 16,500 yr B.P. (Porter and Swanson, 1998), and a series ofproglacial lakes formed. The largest of these is named Lake Russell (Bretz, 1913), and it drainedto the south to the Chehalis River (Thorson 1979, 1980; Waitt and Thorson, 1983). Silt andclay (unit Qvrl) near the Union River was deposited into Lake Russell. At least 20 large deltaswere built out into Lake Russell (Thorson, 1980), and one of these deltas is located in thesoutheastern part of the map area. A foreset-topset transition within these recessional outwashsands and gravels (unit Qvr) at a quarry near McKenna Falls indicates the shoreline elevationof Lake Russell in the map area was 95.7 m (Thorson, 1989). The contact between therecessional lake deposits and the deltaic sand and gravel deposits is gradational and can beseen by examining outcrops along Old Navy Yard Way southwest of Twin Lakes. Otherrecessional outwash sands and gravels were found along the Tahuya River, and near theheadwaters of Big Beef Creek, near, and southwest of, William Symington Lake. Some of therecessional sand and gravel was probably deposited in subglacial channels. The recessionalsediments southeast of Mission Lake cut into the till and the underlying outwash sand andgravel, across the fabric in the fluted till plane. The streams presently occupying this ravineare underfit with respect to the meanders in the ravine, and if the stream formed afterdeglaciation, the stream path would have been parallel to the fluted till surface, rather thanacross it. Thus it probably formed as a subglacial channel. Knob and kettle topography withinwell-sorted sand and gravel in the vicinity of Twin Lakes indicates these recessional sedimentswere deposited in contact with stagnating ice.

Accompanying and outlasting deglaciation was isostatic rebound. Rebound at McKenna

Falls is estimated as 49 m by taking the current elevation of the topset-foreset transition (95.7m) and subtracting the elevation of the Black Lake spillway (46.7 m; see also Thorson, 1989).

The modern depositional environment includes alluvium (unit Qal) and wetland deposits

(unit Qw). There is alluvium along the numerous streams in the map area, but these depositsare almost always too narrow to be mapped at 1:24,000 scale. Many of the wetland depositsare perched on till, indicating the till has poor drainage characteristics. Other wetlands, suchas those surrounded by recessional outwash sand and gravel southwest of Tahuya Lake, appearto be filled kettles, which developed in contact with ice. Human modification of the topographyis mostly seen as artificial fill (unit af) at the Olympic View Sanitary Landfill, near Barney WhiteRanch.

STRUCTURAL HISTORY

It is clear that the Green and Gold Mountains area has been uplifted. However, there is

also an important older structural history related to rifting and emplacement of the sheeteddikes. Clark (1989) found that most dikes had north-northeast strikes, but there was considerablevariation in dike orientations (Figure 1). This suggests there was east-southeast–west-northwestextension at the time of emplacement of the dikes, but perhaps the scatter in dike orientationsindicates emplacement during a transtenstional strain regime where 

σ1 or 

σ2 rotated about

a vertical axis. There is a north-northeast trending magnetic high in the aeromagnetic datathat parallels the trend of the most common dike orientation. This suggests that the dikes maycontribute significantly to the aeromagnetic signature.

Figure 1. Kamb-contoured plot of poles to dikes of diabase and basalt. Black dots are polesto dikes. Data from Clark (1989).

Major faults within the quadrangle strike east-west. The most significant of these is the

Seattle fault, which lies north of Green Mountain, and is indicated by aeromagnetic and gravitysurveys of the region (Blakely and others, 1999a, 1999b). The Seattle fault extends along thesouthern edge of the Seattle basin from the east side of Lake Sammamish across Puget Soundto the Green and Gold Mountains area. On a regional scale, the Seattle fault records southside up motion, indicated by the presence of bedrock uplifts—including Green and GoldMountains, along the south side of the fault (Johnson and others, 1994). Johnson and others(1994) infer that the Seattle fault has been active since the Seattle basin started to form in lateEocene time. We obtained a preliminary apatite fission-track date of 32 

± 5 Ma (Haeussler

and others, 2000) from leucogabbro also dated by Pb-U. This date is consistent with uplift ofGreen Mountain coincident with initial contraction across the Seattle fault and flexural subsidenceof the Seattle basin. We found no evidence in the field or on aerial photographs for surfaceoffset on the Seattle fault in the map area. The Tin Mine Lake fault, which lies between thetwo lobes of Green Mountain, and the Gold Creek fault, which lies between Green and GoldMountains, are indicated by the prominent east-west strike of the valleys they occupy, as wellas by offsets in the ophiolitic pseudostratigraphy. Another roughly east-west striking fault,which we refer to as the Holly Road fault, is located along NW Holly Road, just north of GreenMountain. This fault is indicated by the juxtaposition of submarine basaltic sediments alongthe road with leucogabbro on the north side of Green Mountain at its lowest elevations. Thesimilar strike of the five east-west faults in the map area (the Seattle fault, the Tin Mine Lakefault, the Gold Creek fault, the fault near the Union River Reservoir, and the Holly Road fault)indicate they are related. We infer that the faults have reverse motion, because the Seattle faulthas contractional structures, such as reverse motion fault-cored folds along its strike (Pratt andothers, 1997). Thus, we infer the other east-west faults are probably also reverse faults. Weinfer that the three northern faults are south dipping and that the Gold Creek fault is northdipping, but the dip angle is unconstrained.

Clark (1989) mapped three additional faults with northeast or north-northeast strikes. The

Green Mountain fault is a left-lateral oblique fault, which bisects Green Mountain. Clark (1989)observed left-lateral slickensides on fault surfaces in outcrop. Northwest-side-down sense ofdip-slip motion on the fault is also indicated by offset of the ophiolitic pseudostratigraphy. Onslickensided surfaces, the dip-slip slickensides were the youngest. The Lost Creek fault issoutheast of the Green Mountain fault and has a strike and sense of separation similar to theGreen Mountain fault, and is principally indicated by a geomorphic lineament and offset inthe pseudostratigraphy. The Union River fault, located north of the Union River reservoir,follows a north-northeast trending topographic lineament. West-side-up movement along thisfault is indicated by offset of the ophiolitic pseudostratigraphy.

The relationship between these northeast-striking faults and the east-west striking faults is

uncertain. Clark (1989) concluded the northeast striking faults formed in the late stages of thesame extensional event that produced the mafic dikes, based on his inference that the dip-slipmotion was normal, and on their orientation. If these faults were normal, then the extensiondirection of the most common dike orientation is similar to the extension direction inferredby the faults. If the northeast-striking faults were related to dike intrusion, we suggest therewould be faults that cut the lower, but not the entire, ophiolitic pseudostratigraphy. However,such faults have not been found. We suggest that the northeast-striking faults may be relatedto contractional and/or oblique motion on the Seattle fault and related faults.

Overall, the deformation and fault pattern generally suggests north-south compression after

Crescent Formation time, a conclusion consistent with underthrusting of the Crescent beneathVancouver Island and continued northward migration of the Coast Range in response to obliquesubduction (Clowes and others, 1987; Wells and others, 1998).

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Atwater, B.F., and Moore, A.L., 1992, A tsunami about 1000 years ago in Puget Sound,

Washington: Science, v. 258, p. 1614-1617.

Babcock, R.S., Burmester, R.F., Engebretson, D.C., Warnock, A., and Clark, K.P., 1992, A

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Berggren, W.A., Kent, D.V., Swisher, C.C., III, Aubry, Marie-Pierre, 1995, A revised Cenozoic

geochronology and chronostratigraphy, in Berggren, W.A. , Kent, D.V., Aubry, MariePierre, Hardenbol, Jan, eds., Geochronology, time scales and global stratigraphic correlation:SEPM (Society for Sedimentary Geology) Special Publication 54, p. 129-212.

Blakely, R.J., Wells, R.E., and Weaver, C.S., 1999a, Puget Sound aeromagnetic maps and

data: U.S. Geological Survey Open-File Report 99-514 (URLhttp://geopubs.wr.usgs.gov/open-file/of99-514).

Blakely, R.J., Wells, R.E., Weaver, C.S., and Johnson, S.Y., 1999b, Tectonic setting and

earthquake hazards of the Seattle fault, Washington [abstract]: Implications from highresolution aeromagnetic data: Seismological Research Letters, v. 70, p. 219.

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

Cordilleran ice sheet, Ruddiman, W. F., and Wright, H. E., Jr., editors, North America andadjacent oceans during the last deglaciation, The geology of North America, GeologicalSociety of America, Boulder, v. K-3, p. 71-90

Brandon, M.T., Roden-Tice, M.K., Garver, J.I., 1998, Late Cenozoic exhumation of the

Cascadia accretionary wedge in the Olympic Mountains, northwest Washington State:Geological Society of America Bulletin, v. 110, p. 985-1009.

Brandon, M.T., and Vance, J.A., 1992, New statistical methods for analysis of fission-track

grain-age distributions with applications to detrital ages from the Olympic subductioncomplex, western Washington state: American Journal of Science, v. 292, p. 565-636.

Bretz, J. Harlen, 1913, Glaciation of the Puget Sound region, Bulletin - Division of Mines and

Geology (State of Washington), 244 p.

Bucknam, R.C., Hemphill-Haley, Eileen, and Leopold, Estella, B., 1992, Abrupt uplift within

the past 1700 years at southern Puget Sound, Washington: Science, v. 258, p. 1611-1614.

Clark, K.P., The stratigraphy and geochemistry of the Crescent Formation basalts and the

bedrock geology of associated igneous rocks near Bremerton, Washington, unpublishedM.S. thesis, Western Washington University, Bellingham, 171 p.

Clowes, R.M., Brandon, M.T., Green, A.G., Yorath, C.J., Sutherland Brown, A., Kanasewich,

E.R., and Spencer, C., 1987, LITHOPROBE–southern Vancouver Island: Cenozoicsubduction complex imaged by deep seismic reflections: Canadian Journal of Earth Sciences,v. 24, p. 31-51.

Deeter, J.D., 1978, Quaternary geology and stratigraphy of Kitsap County: M.S. thesis,

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Duncan, R.A., 1982, A captured island chain in the Coast Range of Oregon and Washington,

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on structure and timing of movement of the Seattle fault from structural geology, geophysics,and geochronology of the Green Mountain and Gold Mountain igneous complex, Washington:Geological Society of America Abstracts with Programs v. 32, p. A-16.

Jacoby, G.C., Williams, P.L., Buckley, B.M., 1992, Tree ring correlation between prehistoric

landslides and abrupt tectonic events in Seattle, Washington: Science, v. 258, p. 1621-1623.

Johnson, S.Y., Potter, C.J., and Armentrout, J.M., 1994, Origin and evolution of the Seattle

fault and Seattle basin, Washington: Geology, v. 22, p. 71-74.

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recorded in sediments from Lake Washington, U.S.A.: Science, v. 258, p. 1617-1620.

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retreat of the Puget Lobe of the Cordilleran ice sheet during the last glaciation: QuaternaryResearch, v. 50, p. 205-213.

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Geological Survey Water Supply Paper 1413, 178 p.

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Mountains, Washington: Science, v. 258, p. 1620-1621.

Snavely, P.D., Jr., MacLeod, N.S., and Wagner, H.C., 1968, Tholeiitic and alkalic basalts of

the Eocene Siletz River volcanics, Oregon Coast Range: American Journal of Science, v.266, p. 454-481.

Tabor, R.W., and Cady, W.M., 1978, Geologic map of the Olympic Peninsula, Washington:

U.S. Geological Survey Miscellaneous Investigations Map I-994, scale 1:125,000, 2 sheets.

Thorson, R.M., 1979, Isostatic effects of the last glaciation in the Puget Lowland, Ph.D.

dissertation, University of Washington, Seattle, 154 p.

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

Vashon State (late Pleistocene): Quaternary Research, v. 13, p. 303-321.

Thorson, R.M., 1989, Glacio-isostatic response of the Puget Sound area, Washington:

Geological Society of America Bulletin, v. 101, p. 1163-1174.

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

and Montana: in Porter, S. C., and Wright, H. E., Jr., eds., Late-Quaternary environmentsof the United States: University of Minnesota Press, v. 1, p. 53-70.

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

University of Washington Publication in Geology, v. 4, 266 p.

Wells, R.E., Engebretson, D.C., Snavely, P.D., Jr., and Coe, R.S., 1984, Cenozoic plate

motions and the volcano-tectonic evolution of western Oregon and Washington: Tectonics,v. 3 p. 275-294.

Wells, R.E., Weaver, C.S., and Blakely, R.J., 1998, Fore arc migration in Cascadia and its

neotectonic significance: Geology, v. 26, p. 759-762.

Willis, B., 1898, Drift phenomena of the Puget Sound: Geological Society of America Bulletin,

v. 9., p. 111-162.

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

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

Yount, J.C., Minard, J.P., and Dembroff, G.R., 1993, Geologic map of surficial deposits in the

Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey Open-File Report 93-233, scale 1:100,000.

Equal AreaN = 100 C.I. = 2.0 sigma

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or withthe North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and doesnot imply endorsement by the U.S. Government.This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronicplotters and between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions;therefore, scale and proportions may not be true on plots of this map.For sale by U.S. Geological Survey, Map Distribution, Box 25286, Federal Center, Denver, CO 80225, 1-888-ASK-USGSAvailable on the World Wide Web at http://geopubs.wr.usgs.gov/data.html

GEOLOGIC MAP OF THE WILDCAT LAKE 7.5’ QUADRANGLE

KITSAP AND MASON COUNTIES, WASHINGTON

By

Peter J. Haeussler and Kenneth P. Clark

2000

47° 30 ́

122° 45 ́ 50 47 ́30 ̋  ́ 

50 ́ 47 ́ 30 ̋ 122° 45 ́ 47° 37 ́30 ̋

35 ́

32 ́30 ̋

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

DESCRIPTION OF MAP UNITS

UNCONSOLIDATED DEPOSITS

Post-glacial deposits

Artificial fill (Holocene)—Concrete in dam at northeast end of William

Symington Lake, fill along railroad near Twin Lakes, and sanitary landfillnear Barney White Ranch with modified recessional outwash gravelsand lake deposits

Alluvium (Holocene)—Moderately sorted deposits of cobble gravel, pebbly

sand, and floodplain sandy silt along Stavis Creek and the Tahuya River

Wetland deposits (Holocene and late Pleistocene)—Peat deposits with

some intermixed sand, silt, and clay. Unit commonly occupies shallowdepressions in till (unit Qvt) or low-lying areas of recessional outwash(Qvr or Qva)

Glacial and Interglacial Deposits

Deposits of the Vashon Stade of Fraser Glaciation of Armstrong

and others (1965) (late Pleistocene)—Divided into:

Recessional outwash deposits—Divided into:

Stratified sand and gravel (late Pleistocene)—Stratified and

unconsolidated buff-colored sand and gravel deposits

Ice-contact deposits (late Pleistocene)—Stratified and unconsolidated

buff-colored sand and gravel deposits with pitted outwash topographyin southeastern part of map area. Sediments locally show deformationas a result of sag, slump or collapse.

Recessional lake deposits (late Pleistocene)—Laminated to massive

silt, clayey silt, and silty clay deposited in a lowland lake in thesoutheastern corner of the quadrangle. Inferred as recessionalbecause 1) sediments lie above diamict in boreholes beneath landfillnear Barney White Ranch, and 2) elevation of a foreset/topset bedtransition at McKenna Falls (Thorson, 1989) indicates depositionof sediment into recessional glacial Lake Russell (see Waitt andThorson, 1983)

Till (late Pleistocene)—Compact light to dark gray non-stratified diamict

containing subangular to well-rounded clasts, glacially transported anddeposited. Clasts are commonly granitic and were derived from Canada.Commonly overlies advance outwash deposits (unit Qva) and bedrockon Green and Gold Mountains. Forms undulating surface, with sedimenta few meters to about 20-m thick (Deeter, 1979)

Advance outwash deposits (late Pleistocene)—Stratified to nonstratified gravel deposits. Locally consolidated and hard. Upper meter

may weathered buff to brown. Clasts are usually moderately to wellrounded and less than 40-cm across. Some deposits are diamicts thatwere deposited as debris flows issuing from front of advancing ice sheet.Debris flow deposits differentiated from till by: 1) lack of clasts largerthan 40-cm, 2) large cobbles commonly touching rather than matrixsupported, 3) high proportion (roughly 40% or more) of large clasts,and 4) usually not as hard as till

Pre-Vashon deposits, undifferentiated (Pleistocene)—Glacial and

interglacial sediments, inferred to underlie Vashon-age deposits andshown only on cross section

BEDROCK

Stratified rocks

Blakely Formation (Upper Eocene and Oligocene)—Siltstone, sandstone,

lapilli tuff, and pebble to cobble conglomerate. Most of section is ofOligocene age, but also includes late Eocene forminifera of the RefugianStage (see Yount and Gower, 1991). Appears only on cross section,where it is inferred north of the Seattle fault

Crescent Formation (Middle Eocene)—Divided into:

Massive basaltic lava flows—Lavas contain pyroxene phenocrysts and

calcite- or zeolite-filled amygdules. Texture in thin section is intergranular,with rock consisting of 45% labradoritic plagioclase, 35% augiticclinopyroxene, 15% opaques, and minor olivine and orthopyroxene.Individual flows are typically 10-m thick. Inferred to be subaerial becauseof a lack of interbedded sedimentary rocks. Exposed thickness is at least180 m, but may be more than 1-km (Clark, 1989)

Submarine basalt and related volcaniclastic rocks—Dominantly

greenish-weathering submarine basalt flows interbedded with tuffs, tuffbreccias, basaltic breccias, graded lithic and tuffaceous sandstones,basaltic siltstones, and conglomerates. No pillows recognized, vesiclesare generally filled with calcite. In thin section plagioclase typicallycomposes about 50% of the rock, clinopyroxene 35%, and opaquesabout 10%. Sedimentary interbeds usually less than one meter thickand up to 10-m thick. These volcaniclastic rocks include altered lithictuffs, volcanic breccias, aquagene crystal-lithic tuffs, graded basalticsandstones and siltstones, and welded tuffs. Approximately 180-m thick.Intruded by dikes of basalt and diabase of unit Ted

Felsic volcanic(?) rock—Fine-grained pinkish-orange to brown weathering

amygdaloidal quartz latite. Forms tabular bodies that could be eitherconformable interbeds or younger sills in submarine basalt. Probablehigh-level or extrusive equivalent of felsic intrusive rock, unit Tef.Intergranular porphyritic or intergranular glomeroporphyritic; alterationminerals comprise about 50% of rock

Intrusive rocks

Porphyritic and aphanitic andesite and dacite dikes (Eocene?)

—

Medium to light grey. Dikes cut all other bedrock units. In thin section,consists of of about 50% plagioclase, 5-20% quartz, and 10-15%amphibole, and about 15% other mafic minerals. Textures are, indecreasing abundance, pilotaxitic porphyritic, glomeroporphyritic witha felty groundmass, and hyalopilitic

Felsic intrusive rocks (Eocene?)—Quartz monzonite, quartz diorite,

tonalite. Texture in thin section is intergranular granophyric. Intrudesbasalts that appear to cut leucogabbro of unit Teg

Sheeted dikes of basalt and diabase (Eocene)—Sheeted dikes are dark

greyish black on fresh surfaces and weather bluish to greenish grey.Dikes are a few centimeters to 10-m wide, but are most commonly 1-m wide. Dike margins are chilled on either one or both sides. Texturesrange from very fine grained to diabasic and microgabbroic. Augite isdominant pyroxene in thin section. Dikes are amygdaloidal where theyintrude the overlying submarine basalts and sediments. Zone consistingentirely of dikes is about 150-m thick

Leucogabbro and pegmatite intruded by dikes of basalt and

diabase (Eocene)—Leucogabbro and pegmatite, described in unitTegd, either fine or coarse grained occur as screens between dikes ofbasalt and diabase. Dikes, of unit Ted, are up to 10-m wide but arecommonly 1-m wide. Medium grey on fresh surfaces, weathers lightgray to orange gray

Leucogabbro and pegmatite (Eocene)—Massive leucogabbro, either

fine or coarse grained. Medium grey on fresh surfaces, weathers lightgray to orange gray. Texture in thin section is intergranular andglomeroporphyritic with phenocrysts of plagioclase and less commonlyaugitic pyroxene. Plagioclase ranges in composition from labradoriteto bytownite. Overall rock composition is approximately 45% plagioclase,40% clinopyroxene, up to 5% brown hornblende, and 5% opaques.The brown hornblende is interstitial to other mineral phases. ‘Pegmatoid’denotes very coarse grained intrusive rocks associated with the leucogabbro.End members of the pegmatoid are gabbroic and granophyric. Gabbroicpegmatoid has intergranular texture with ophitic to subophitic plagioclasegrains to 3-4 cm. Rock composition is approximately 45% plagioclase,40% clinopyroxene, and 5-10% magnetite. Granophyric pematoid isintergranular granophyric with grains to several centimeters across andan overall composition of 40% oligoclase, 10-20% pyroxene, 25%quartz, 10% micrographic regions, up to 10% magnetite, and minorepidote and microcline

Ultramafic rocks (Eocene)—Ultramafic rocks beneath Green and Gold

Mountains inferred from modeling aeromagnetic and gravity data. Shownonly on cross section. Rocks must be dense and magnetic

Tb

Tcb

Tcbs

Tcfv

af

Qal

Qw

Qvr

Qvt

Qva

Qpvu

QvrlQvri

Version 1.0

Preliminary geologic map of the Wildcat Lake 7.5’

quadrangle Kitsap andMason counties, Washington

OPEN-FILE REPORT 00-356

Tefv

Ted

Tad

Teum

Teg

Tegd

CREEK

Qvt

Qva

Qva

Qw

Qw

Qw

Qvr Qw

Qva

Qw

Qva

Qvr

Qvr

Qvr Qvr

Qva

Tcbs

Teg

Tegd

Ted Tcbs

Tefv

Tcfv

Tcfv

Qva

Qva

Tegd

Tegd

Qvt

Qvt

Tegd

Tegd

Qva

Qvr

Qw

Tegd

Qw

Qvr

Ted Tegd

Tcbs

Ted

Tcbs

Qw

Tegd

Qvt

Ted

Tef

Tcbs

Tegd

Tegd

Qw

Ted

Qva

Tef

Qw

Qvr

Ted Ted

Qvr

Tegd

Tegd

Qw

Ted

Tcbs

Tegd

Qw

Qw

Teg

Qvt

Ted

Teg Tcbs

Qw Qw

Ted

Teg

Tcbs Ted Qvr

Qvt

Qw

Qvt

Qw Qvt Qvt

Qw

Tcbs

Qw

Qvr Qvt

Qw Qw

Qvr

Qva

Tcbs

Tcb

Qvr

Qvt

Qvt

Qw

Qw

Qw

Qw

vt

Qw

Qw

Qvr

Qvr

Qvt

Qvt

Qva

Qva

Tcb

Qva

Qvi

Qvr

Qva

Qw

Qw

Qvrl

af

Qw

Qw

Qw

Qvt

af

Qvt

Qva

Qvt

Qva

Qva

Teg

Qvr

84

50

75

85

45

75

85

75

82

83

65 60 50

45

85

60

72

85

38

87

70

75

40

50

50

30

52

88 47

35

58

50

49

41

45

82

58

85

82

67

74

85

33

85

41

51

72

49

71

65

86

82

70

74

70

65

74

70

86

75

56

22

10

24

29

42

33 27

30

25

23

25

40

22

15

52

20

10

33

30 11

19 23

13

45

24

45

20

20

15

4

A

SEATTLE

FAULT

HOLLY

ROAD FAULT

LAKE

FAULT

?

TIN

?

MINE

MOUNTAIN

FAULT

?

?

?

?

FAULT

GREEN

?

?

GOLD

A’

?

?

?

Qvt

GREEN MOUNTAIN FAULT

CORRELATION OF MAP UNITS

QUATERNARYTERTIARY

HolocenePleistocene

Unconsolidated and

stratified rocks

Intrusive rocks

Tb

Unconformity

Qvt

af Qal

Qvr

Qva

Qpvu

middle Eocenelower Eocene

Eocene(?) Tad

Tcfv Tefv

Teum

Ted

Tegd

Teg

Tcb

Tcbs

Unconformity

upper Eocene

and Oligocene

Qw

Qvri Qvrl

Strike and dip of dikes

basalt and diabase of unit Tedandesite of unit Tad

85

86

Strike and dip of beds

InclinedHorizontal

15

EXPLANATION

Contact — Dashed where approximately locatedContact — Gradational between igneous unitsFault — Dashed where approximately located; dotted where concealedFault — 

U, upthrown side; 

D, downthrown side

Reverse fault —Dashed where approximately located; dotted where

concealed

Fault — Showing relative horizontal movementPb-U and apatite fission track sampling locality

D

U

Teum Teum Teum

Teg

Teum

Teum

Teg

Teg

Teg

Teg

Teg

Teg

Teg

Ted

Ted

Ted

Ted Ted

Ted

Tegd

Tegd

Tcb Tcbs

Qvt

Tcbs

Tcfv Tcbs

Tefv

Tegd Qvr Tcbs

Qvt

Tegd

Tcbs Tcb

Tegd

Tegd

Qvt

Qva

Qpvu

Qvt Qva

Qvr Qvri Qvrl Qvr

Qvt

METERS

100200

300

400

SEA LEVEL

500600

100200

300

400500600700800900

A’

GOLD MOUNTAIN

GREEN MOUNTAIN

Big Beef Creek

SEATTLE FAULT

HOLLY ROAD FAULT

TIN MINE LAKE FAULT

LOST CREEK FAULT

GOLD CREEK FAULT