GM-56, Geologic Map of the East Olympia 7.5-Minute Quadgrangle

WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES GEOLOGIC MAP GM-56 Division of Geology and Earth Resources Ron Teissere - State Geologist 122°52¢30² R2W R1W 50¢00² 47¢30² 122°45¢00² Budd Inlet Nisqually R. 47°00¢00² 47°00¢00² Henderson Inlet ket Qgtn1 INTRODUCTION ice marginal streams originating in the Nisqually and Lake St. Clair area Vashon recessional outwash gravel, train 2—Loose sandy Qgok Qgokb Qgok Qgosk Qgo Qp and farther east from glacial Lake Puyallup to flow westward across the n2 gravel; tan to gray; moderately to well rounded; moderately to Qp The East Olympia quadrangle is traversed by the geophysical lineament northern half of the map area, cutting channels through the Vashon well sorted; consists of plutonic and metamorphic clasts Inlet Qgos Qp Qgosk Qgosk known as the Olympia structure (Logan and Walsh, 2004; Magsino and T18N T18N ground moraine and into underlying advance outwash. As the energy of transported by Vashon ice and deposited by meltwater. Qgos Qf Qgosk others, 2003; Sherrod, 2001) (Fig. 1). An aeromagnetic and gravity T17N Qgok these streams waned, they eventually deposited sand and gravel, followed Because the unit is so flat and loose, outcrops are rare and T17N lineament along the projection of the Olympia structure occurs to the Qgos by sand and silt, around the remaining stagnant ice blocks. As the ice limited to surficial regolith. This unit forms a terrace that northeast of the Eocene-bedrock-cored hills near Tenino (Gower and Qa Qgo Qgos melted away, the Budd Inlet, Henderson Inlet, and Nisqually kettle chains resulted from the northward migration of and downcutting by kb others, 1985), but is masked by glacial drift, which covers most of the were formed. the same ice-marginal streams that deposited unit Qgo . tletle traintrain n1 AIN Qgo area. Glacial ice and meltwater deposited drift and carved extensive areas Qf k Soils capping bedrock areas tend to be reddish brown, but those Stagnant ice from south of Lake St. Clair (Fig.1) was the OLYMPIA into a complex geomorphology that provides insight into the glacial Black Qgos capping most glacial outwash deposits tend to be very dark brown to probable source for most of the ice-marginal flow. This terrace fk Qp processes that occurred at the end of the Pleistocene. The many Hills Qgok black. The soils covering unit Qgo are formed into mounds about 2 to 6 was formed as the snout of the glacier was retreating LOBE Qgokb streamlined elongate hills (drumlins) reveal the direction of ice y3 Qgos ft high and 10 to 30 ft across. The mounds are referred to as Mima northward. Several kettles formed in this unit, indicating that lele traintrain Qp movement throughout the map area. Mima mounds (Washburn, 1988) Qgosk mounds and have been extensively studied by previous workers stagnant ice was trapped during the deposition of the unit. OLYMPIA Qa cover terraces in parts of the quadrangle. Lidar imagery was used to OLYMP kett Qgokb Qgos (summarized in Washburn, 1988; and discussed in Bretz, 1913). It is TERR Qml Qgos Qp k interpret and map landforms, which were then field mapped and checked Vashon recessional outwash gravel, train 1—Loose sand Lake St. Qgokb notable that unit Qgo is the only unit within the East Olympia Qgo YELM y3 n1 Clair against water-well logs to confirm their inferred underlying geologic and gravel; tan to gray; moderately sorted; moderately to well East Olympia quadrangle Qgok quadrangle on which the Mima mounds formed (this study; Pringle and materials. rounded. Sand grains from a gravel pit in sec. 26, T17N R1W, Budd IA SSTRUCTURE Pattison Goldstein, 2002). The mounds must have formed very shortly after unit Nisqually LOBE Qgosk are about 90 percent northern source, being dominated by TRUCTURE Qgo was deposited, because (1) they did not form within kettles, which Deschutes R Lake y3 Qgos Inlet kett Qgos GEOLOGIC HISTORY polycrystalline quartz, with about 10 percent or less glassy, Qgos Qgos clearly formed after unit Qgoy3 was deposited (kettles crosscut meltwater Qf porphyritic volcanic clasts, probably from the local Cascade Qp channels); (2) they appear to be partially buried by alluvial fans near the Qgos Bedrock exposure is most abundant in the hills southeast of Offutt Lake Range, indicating that the unit was deposited mostly from Chambers Prairie n4 and in the upper reaches of the Deschutes River where it consists margins of the unit Qgoy3 channel; and (3) they did not form in unit Qgoy4 le t R. OBE Qgok glacial meltwater from stagnant ice south of Lake St. Clair channels that cut the surface of unit Qgo . Qgo Qgok Qgos primarily of thinly bedded siltstone, tuff breccia, and thick sandstone of y3 (Fig. 1). The unit forms terraces that were probably deposited rain LOBE TERRAIN Qgo Qga Snavely and others (1958) mapped broad southward-plunging folds kb Qgos the Eocene McIntosh Formation (unit Emm), which was named and by earlier stages of the same ice-marginal streams that East in bedrock directly south of and projecting into the map area. The few y4 Qgtn1 mapped by Snavely and others (1958) south of the project area. Qgo Olympia Qml deposited sediment on unit Qgtn2. Additional isolated outcrops, mostly of volcanic breccia, are scattered attitudes collected from sparse outcrop during this study support the Qgo Qa Qgos general structural interpretation of these earlier workers. Vashon recessional outwash gravel in kettle walls—Loose n2 Qgos Qgos throughout the glacially scoured hills north, east, and west of Offutt Lake n4 Sheehan Qgo Qgok McCORKLE n2 Yelm Qgtn1 Qgtn1 and are mostly interpreted as McIntosh Formation interbeds. However, an We have mapped a northwest-trending fault in the southeast corner of sand and gravel; tan to gray; moderately to well rounded and Lake Qgo CHANNEL n4n4 n3 Qgok Qgtn1 Qga outcrop due west of Offutt Lake contains a porphyritic volcanic rock of the quadrangle (cross section B), based on its topographic expression and sorted; consists of northern-source plutonic and metamorphic Qgo Qga Tempo INTERINTERL unknown affinity with a chilled margin in contact with a coarse-grained oil and gas test well logs. The fault is covered by Quaternary sediment rock carried by Vashon ice and porphyritic volcanic rock from Qgo n1 Qga Lake Qgo Qgok Qgtn1 mafic intrusive (unit Eig). Although unit Eig has similar mineralogy and and was not observed in outcrop. It parallels the upper Deschutes River the Cascade Range. In the northwestern part of the map, where Qgok OLYMPIA LOBE Qgo OLYMPIA LOBE y2 YELM LOBE Qgokb petrographic texture (subophitic) to gabbro and diabase found in the valley, which dissects the till-covered hills in the south half of the exposed near the Deschutes River valley, consists of sandy Offutt y4 Qgok CHANNEL Qgo Qga Qgt Crescent Formation, the chemistry of this unit is much more mafic quadrangle and is itself parallel to and along trend with the structure gravel; farther south near Offutt Lake, kettle sides contain Lake Qgo y1 YELM CHANNEL n1 Qgt y3 Tenalquot Qgt known as the Olympia structure (Magsino and others, 2003; Sherrod, boulder and cobble clasts. n1 (Table 1) (Phillips and others, 1989) and a radiometric age of 38.76 Prairie Qgo 2001). Based on continuity of bedrock structure across the Deschutes e Qgok ±2.50 Ma obtained in this study indicates that is too young to be Qgokb Vashon Recessional Outwash, Yelm and Olympia Lobe Sources Crescent, but is about the same age as either the volcanic rocks of Grays River valley and interpretation of aeromagnetic data of Blakely and o1? o3 River (Walsh, 1987; Phillips, 1987) or Northcraft Formation, both of others (1999), we place the Olympia structure northeast of the hills There were four distinct trains of recessional outwash from the Yelm y3 Qgo Qp containing Tempo Lake as shown in Fig. 1, although no surficial Qgo Qgo Qa Qgos which are present nearby. Chemically, it is strongly tholeiitic, like the lobe. They are represented, from youngest to oldest, by units Qgoy4, Rocky Prairi YELM LOBE Qgos Qgt Qga and kk n1 volcanic rocks of Grays River and unlike the Northcraft Formation, expression other than the northwest trend of the hills was detected in lidar Qgo , Qgo , and Qgo . Meltwater from the Olympia lobe incised into RAINIER CHANNEL Qgtn1 y3 y2 y1 Qgo Rainier imagery or on the ground. o2o2 Chain y1y1 which is transitional tholeiitic to calc-alkaline. Unit Eig also contains units Qgoy1 and Qgoy2 depositing units Qgoo1through Qgoo3. Subsequent Chain y2 Qgok CreeCree Hill Qgo Qgos large (1–2 cm) augite crystals similar to those found in some volcanic meltwater from the Yelm channel truncated both the earlier Yelm and y3 Qga Qgos QgoQgo y3 Qgo Qgok rocks of Grays River in the Doty Hills (Walsh and others, 1987), so we DESCRIPTIONS OF MAP UNITS Olympia lobe outwash channels and deposited units Qgoy3 and Qgoy4. Qgo Qgokb tentatively correlate these rocks with the volcanic rocks of Grays River. Quaternary Unconsolidated Deposits The listing below reflects the chronologic order of these events. Qgo Qgtn1 This exposure is somewhat outside of the outcrop area of Grays River, Tenino kb Vashon recessional outwash, Yelm lobe, Rainier channel, McIntosh however, and may represent a different pile extruded in the same tectonic HOLOCENE NONGLACIAL DEPOSITS Qgo Qgok Qga y4 Qga Deschutes River—Loose sand and gravel; grains and clasts iit Lake y3 and Qgo environment. lliim Qgo y4 Qgo Fill—Generally large engineered fills of unknown materials well rounded; moderately to well sorted; restricted to channel e Deschutes R. 57¢30² kb Qgtn1 57¢30² The Pleistocene history of the Puget Lowland was described in detail Qf iic Scatter Qgokb .

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