GEOLOGIC MAP of QUATERNARY UNITS in the WILLAMETTE VALLEY, OREGON and Modified by the State of Oregon, 1994; U.S
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U.S. DEPARTMENT OF THE INTERIOR Prepared in cooperation with PROFESSIONAL PAPER 1620 U.S. GEOLOGICAL SURVEY OREGON WATER RESOURCES DEPARTMENT Quaternary geologic units in Willamette Valley, Oregon—PLATE 1 O'Connor and others, 2001, Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon. 123°45' R. 7 W. R. 6 W. R. 5 W. 123º30' R. 4 W. R. 3 W. 123º15' R. 2 W. R. 1 W. 123°00' R. 1 E. R. 2 E. 122°45' R. 3 E. T. WASHINGTON MULTNOMAH T. 1 Gaston 205 1 S. COUNTY COUNTY S. Tigard Lake Turner Oswego Tua 99W 5 latin Clackamas ego Osw DESCRIPTION OF MAPPING UNIT CORRELATION OF MAP UNITS ake T. Creek L T. 2 Clackamas 2 S. Tualatin River Clear S. Alluvium of smaller streams (Holocene and upper Pleistocene)—Unconsolidated clay, silt, sand, and minor gravel VK Gladstone Qalf Age (Ma) 25 QTg River deposited in floodplains and active channels of smaller streams and rivers. Variable surface morphology. Thickness not Qalf defined, but probably less than 10 meters. Differentiated from units Qbf and Qau where clearly younger than Missoula Tvc Tcr Qff2 Tcr Qff2 QTb QTb 0 hill Qff2 West Linn Qalc Flood deposits. Mostly younger than 12 ka. Yam Tm Qff2 Qalf C Rock Creek North Qau Sherwood Willamette QTt Qalf Qalc h Gap Falls Creek e QTt Holocene River k h e a Tm e Qau Floodplain deposits of the Willamette River and major tributaries (Holocene and upper Pleistocene)— l r Qfc QTb W e C Tcr Oregon Qalc m Tm Tcr Unconsolidated silt, sand, and gravel of the Willamette River and major Cascade Range tributaries. Includes active il Qfc la r City 0.01 da channel and modern floodplain surfaces. Meander-scroll topography with surfaces as high as 15 meters above summer m e QTg Disconformity e Tm t Haskins C Qalf water stage. Drillers' logs and exposures indicate that unit thickness ranges up to 15 meters. Isotopic dating, t Tcr e Qalf Cre b ek Qff RM tephrochronology, and stratigraphic relations within the Willamette Valley indicate that these deposits are mostly younger a Qalf 2 Qff2 s Creek 30 than 12 ka. i T. n Qff Qff2 Qg T. b 2 Tcr Newberg Wilsonville 3 1 3 o A u Qff b S. n Panther Qfc 2 e Sand and Gravel that postdates Missoula Floods (upper Pleistocene)—Alluvial sand and gravel deposited in broad S. d r a Tm Qff Qff n Qg r Carlton Tcr 1 Qff 2 e 1 braidplains within Willamette Valley and traced upstream as alluvial fills in major Cascade Range tributary valleys. Forms y Tcr 2 t Disconformity h RM Qfc QTt y surfaces of large fans where major Cascade Range tributaries enter the Willamette Valley. Deposits now preserved as Molalla QTb RM Qfc VK 40 C planar to slightly undulating terraces 0 to 15 meters above the modern floodplain. Drillers' logs and stratigraphic exposures Creek 50 50 r e indicate that unit is up to 30 meters thick. Stratigraphic relations and isotopic dating indicate that deposits primarily date Qau Qbf Qls QTt e k from about 12 ka, although some areas mapped as Qg in the Eugene-Springfield area and within the Cascade Range Qff1 Qff Canby 1 Qalc 1 Qalc foothills may be substantially older. 45°15' Qff Tcr 45°15' Qls 1 River reek QTb Disconformity C Qalf 5 n Aurora Missoula Flood deposits (upper Pleistocene)—Unconsolidated clay, silt, sand, and gravel deposited by floods o COUNTY i Pleistocene QUATERNARY Yamh s Creek il s originating in glacial Lake Missoula that flowed down the Columbia River and backflooded into the Willamette Valley l i TILLAMOOK Baker Qff Creek M 2 (Glenn, 1965; Allison, 1978). Largest flows reached stages of about 120 meters above sea level in the map area. T. Gribble Qalf Qff Qfc Dayton St Paul Qff2 T. 2 4 McMinnville QTb 4 Maximum thickness of deposits about 35 meters in northern Willamette Valley, thins to less than 1 meter at elevations S. Qalf Creek S. above about 100 meters. Radiocarbon dating, tephrochronology, and stratigraphic relations from within and outside the Qff River Weston 2 Rock map area indicate that most units date from about 15 to 12.7 ka. Divided into: Disconformity Landing RM Qg1 Bear QTt 60 99E Younger and lower fine-grained Missoula Flood deposits—Clay, silt, sand, and minor gravel forming benches along Qff Champoeg Creek Muddy 2 VK Qg2 Qff Qg River 1 Labish channel and Pudding River, and locally flanking Willamette River in northern Willamette valley. Planar to 2 iver Creek 75 R Qalf Mill Creek Qau undulating surface almost everywhere 40-50 meters above sea level. Set into main-body fine facies (Qff ). Probably Qalf Qalf Creek 2 Tvw Qalf mostly deposited by latest Pleistocene Missoula Floods between 13.5 and 12.7 ka, but possibly includes late Pleistocene River and early Holocene deposits of units Qalf and Qalc. Unconformity Bend QTt Molalla Tm Woodburn QTt Creek Main body of fine-grained Missoula Flood deposits—Stratified silt and clay with minor sand. Underlies much of T. Deer Qff T. Qff Creek l 2 2 Willamette Valley lowland floor. Many sections show rhythmic bedding, with up to 40 individual beds between 0.1 and 5 l Tvw 5 i Qau QTg S. h Palmer S. 1.0 meter thick. Encloses sparse pebbles to boulders of types exotic to Willamette Basin. Forms undulating to planar QTb 1.6 m Tm Rock QTt a Y topography in lowlands; mantles foothills below altitudes of 120 meters. Mapped where thickness is sufficient to Amity Tcr Qg1 Pudding Butte Creek Pliocene RM Gervais QTg obscure previous topography. Commonly capped by up to two meters of late Pleistocene and Holocene alluvium, Creek 70 QTg Qau Sheridan Tm Qff2 Qalf colluvium, and loess. Creek Conformity to Disconformity 5.0 Tcr Qg1 E ER Wheatland IV O R Qau Coarse Missoula Flood deposits—Bouldery, cobbly, sandy gravel fans deposited by Missoula Floods as they spilled Ferry Tcr h Tm L Qalf Sout Mount Qfc into northern Willamette Valley through the Oregon City and Rock Creek gaps. Crudely stratified, commonly with YAMHILL COUNTY A A Tcr Angel Tvw south-dipping foresets. Commonly capped by several meters of sandy silt, especially south of Willamette River. Drillers' Miocene QTg POLK COUNTY H Tm A' logs indicate that thickness locally exceeds 30 meters. I Unconformity L ek Swale Tcr Tcr Qau Tvw re L Qalc Qalf C Sand and gravel that predates Missoula Floods (Pleistocene)—Unconsolidated to semiconsolidated sand and gravel Qalf S QTg Qff2 Tcr 1 Qau Tm 24 k Qff T. Qg TERTIARY T. Tm e 2 deposited in broad braidplains and meandering floodplain environments within Willamette Valley and upstream as alluvial e r el Qau 6 6 E n Abiqua Tm Tm C n fills along major Cascade Range tributaries. Locally contains lahar deposits. Forms planar to slightly undulating terrace Tm T a Scotts Mills Tcr Tcr S. h Oligocene S. T y C r h e surfaces 0 to 20 meters above the modern floodplain and generally at slightly higher elevations than adjacent surfaces of E Tcr e s Qff Qau l i 1 v l b i M a a R unit Qg . Thickness not systematically determined but locally exceeds 100 meters in broad fans formed where major L A QTg 1 V t Qau L g 38 l g n Cascade Range tributaries enter the Willamette lowlands. Isotopic dating and tephrochronology indicate these deposits a Sprin L i Coal Tvw QTg I Qff River S Tm 1 d 22 d range from greater than 0.41 Ma to about 22 ka. E W u Tm Creek Tm O P QTg 45°00' Tm Qau 45°00' Eocene Tvc L e Tm l Silverton Alluvium, undifferentiated (Holocene and Pleistocene)—Sand, silt, clay, and minor gravel deposited by smaller streams r Keizer t Butte Qau A t C i Qau t Tm and rivers that enter the Willamette Valley, and by larger streams and rivers outside the area of detailed mapping. Age and l Tm Hayesville L a RM Creek S H Silver thickness not determined. k Qau 80 Tcr I F Tcr QTg L Tm W Tm Creek Tvc L QTg Fine-grained alluvium (Holocene and Pleistocene)—Clay, silt, sand, and minor gravel deposited in small basins Drift S Tcr Qbf Tm Pudding Qau T. flanking the Willamette Valley. Planar surfaces. Age and thickness not determined. Distinction with unit Qau locally Qff T. 2 Qff2 7 7 Qls arbitrary. Bask VK SALEM S S. S. Tm ett 100 5 L I L Landslide deposits and colluvium (Holocene and Pleistocene)—Unconsolidated and heterogeneous mixtures of rock QTg Qau Slough H Eola Tm Creek Qls fragments and soil. Some landslide deposits have hummocky surfaces. Colluvium mapped on steep debris-mantled slopes O QTg D Tvw where underlying bedrock is not known. Only larger deposits mapped, mostly after Walker and McLeod (1991). Age and Qau Qg L CLACK Tvc Creek Qalf 1 A Tm A RM Tvw M thickness not defined. QTg QTg Qg W A Dallas Rickreall 1 90 Tm MA S 1 R Qg Creek IO COUNTY N Fk Qff2 Qls N Weathered terrace gravel (Pleistocene and Pliocene?)—Alluvial sand and gravel preserved as terraces flanking Qau 99W Qg1 River Tvw Bend Tcr CO QTg Willamette Valley and tributary valleys. Terrace surfaces planar to undulating, with thick, strongly-developed soils, and Tvc UNTY Qff2 S&G Tm severely weathered clasts. Terrace surfaces up to 100 meters above modern floodplains. Drillers' logs and stratigraphic Tm 99E Tvw Ash Tvw exposures indicate sand and gravel 0 to 60 meters thick.