(LACAMAS CREEK) U.S. Department of the Interior Scientific Investigations Map 3257 U.S. Geological Survey Pamphlet accompanies map

122o22'30" o (BOBS MOUNTAIN) 549000mE 550 551 1 530 000 FEET (OREG.) 20' 553 (LARCH MOUNTAIN) 554 555 17' 30" 556 557 1 550 000 FEET (WASH.) 558 C' 122 15' 45o37'30" 45o37'30" CORRELATION OF MAP UNITS deposition behind the immense Missoula flood bar extend- May locally include compositionally similar loess. Region- poorly known but probably ranges from middle Miocene basalt flows in the Columbia Basin. Nomenclature follows percent; as large as 7 mm across), olivine (9 percent; 1 to Ttfc Ttfc 3 20 Tbem Ta Tsr Tsr Ttfc Tt Qls Qa 19 Tt [Age of epoch boundaries from time scale of Ogg and others (2008). 40Ar/39Ar ages shown are from table 2] ing southwestward of Broughton Bluff (Evarts and ally correlative to Trimble’s (1963) Quaternary lacustrine to middle Pliocene; in Mount Norway area, well logs Swanson and others (1979) and Beeson and others (1985) 2 mm across; slightly altered to smectite), and augite (1–2 26 Qtdwu Qtdw 18 Ta u Qtdw Approximate Qa 1 Tbem Ta u O’Connor, 2008) that temporarily blocked the Sandy River deposits (Qlg), but he shows no such deposits in the map indicate unit underlies the conglomerate member of the percent; 0.5 to 1 mm across) in a coarse intergranular Ttfc Ttfc age in Ma SURFICIAL DEPOSITS Priest Rapids Member—Uppermost member of the Qa Qa Qls area Ttfc 0 at its confluence with the Columbia River. Equivalent to Troutdale Formation ( ) along a sharp, probably Wanapum Basalt (Swanson and others, 1979). In this quad- groundmass of plagioclase, augite, and Fe-Ti oxide. Qls Tbem Tbem 40 Tob Ttfc Tvs 5052000mN Tbem Qa 110 000 FEET af Sandy River terrace deposits (Qtds) mapped in adjacent Qfg unconformable, contact, whereas to west of map area, it Exhibits low-potassium tholeiite chemistry 11 (WASH.) Qh Gravel facies—Unconsolidated, gray, stratified, bouldery to rangle, represented by a single intracanyon flow Qtdl Qtdw Qe Qac Camas quadrangle (Evarts and O’Connor, 2008) and cobbly gravel and sand organized into prominent large bar underlies or is interbedded with lower part of hyaloclastic Tbem Ttfc Tsr l Qls Qa A' 0.0002 Twpr Basalt of Rosalia of Beeson and others (1989)—Thick Basaltic andesite of Elkhorn Mountain of Evarts (2006b) Qt Sandy River Washougal River Holocene equivalent in part to Estacada Formation of Trimble (1963) sandstone member of Troutdale Formation (Ttfh) (Evarts r Qls Qa along lower reach of Washougal River. Base not exposed, (Oligocene)—Sequence of lava flows and flow breccia Tsr terrace deposits terrace deposits flow and associated hyaloclastite of olivine- and Ttfc Qa and O’Connor, 2008) inferred to be about 3 to 4 m.y. old; Qtdwl Qtds2 Terrace deposits 2 (Pleistocene)—Unconsolidated sandy but bars reach heights of 20 m above enveloping Columbia composed of dark-gray to brown, porphyritic to seriate to Qtdwu plagioclase-microphyric basalt; fills paleocanyon cut into Qa Qmbp Qt Qls Qt Qtds Qtdw River floodplain. Well logs west of map area indicated plant fossils from localities near top of unit along Sandy Qa Ttfc Qa Qls 1 l gravel underlying distinct benches along the Sandy River Frenchman Springs Member, Grande Ronde Basalt, and aphyric tholeiitic basaltic andesite and basalt; unit locally Qa ? River just south of quadrangle assigned an early Pliocene Ttfc 39 ? valley; as thick as 20 m but only exposed along steep total thickness locally as great as 68 m (Hoffstetter, 1984; older rocks (Waters, 1973; Tolan, 1982; Tolan and Beeson, includes minor volcaniclastic rocks too small or poorly Qt Cataclysmic-flood desposits age (Chaney, 1944; Treasher, 1942; Trimble, 1963; Tolan valley slopes and in cuts along roads and tracks descending Hartford and McFarland, 1989). Texturally and composi- 1984); approx 200 m thick near southwest margin of paleo- exposed to map. As thick as 1.3 km in map area. 10 29 0.015 Qtdw Qtdl tionally variable; most clasts derived from Columbia River and Beeson, 1984) Qls Qlo Qfs Qfg u to valley bottom. Consists of subhorizontal gravel sheets, canyon at Chanticleer Point; more than 220 m thick along Individual flows generally about 5 to 8 m thick and Qtdw Qls Qa l Tbem 0.5–5 m thick, locally separated by thin sand lenses; poorly Basalt Group but also includes blocks of Troutdale Forma- axis of paleocanyon at Crown Point, just east of map area exhibit platy to blocky to columnar jointing. Typical Qls Qa Ta sorted, locally imbricated, minimally weathered; varies tion and Pliocene–Quaternary Cascadian basalt, all prob- VOLCANIC ROCKS OF THE BORING VOLCANIC FIELD flows contain phenocrysts and glomerocrysts of weakly 50 Qmmn (Tolan, 1982). Lava flow, with thin colonnade and thick, 51 Tvs 41 ? ? from compact clast-supported boulder and cobble gravel ably entrained in western Columbia River Gorge. Likely zoned plagioclase (0–25 percent; 1 to 6 mm, rarely more Tbem 41 5051 Qtds Qmmn Basaltic andesite of Mount Norway (Pleistocene)-Light- hackly jointed entablature, sharply overlies and locally 2 with sand matrix to loose open-work cobble gravel; suban- deposited during multiple flood events between 20 and 15 than 10 mm long; variably replaced by zeolites and (or) 17 693±9 ka gray, aphyric, pilotaxitic, calc-alkaline basaltic andesite invades stratified hyaloclastite, which constitutes 25–60 15 gular to well rounded clasts include common large (to 1 m ka (Benito and O’Connor, 2003; O’Connor and Benito, clay) and olivine (<3 percent; 0.5 to 3 mm across; com- 9 percent of total thickness (Tolan, 1982; Tolan and Beeson, (56–57 wt percent SiO2) underlying area around Mount Tsr? Qtds diameter) boulders of hornblende andesite, especially near 2009). Finer sand facies probably deposited by late floods monly partly resorbed and surrounded by rinds of granular Tsr Qtdw ? 3 Norway (Trimble, 1963; Allen, 1975; Mundorff, 1964); 1984); locally grades laterally into pillow-lava zones, QTc Qtdwl l base. Overlies hyaloclastic sandstone member of the confined to Columbia River valley. Mostly equivalent to pyroxene and (or) magnetite; rarely contain minute chro- T 2 N 42 T 2 N very platy flow with weathered vesicular flowtop well which are unrelated to basal hyaloclastite (Waters, 1973; Qa Qt Troutdale Formation (Ttfh) at elevations between 140 and Trimble’s (1963) Quaternary lacustrine gravel (Qlg) but mian spinel inclusions; almost invariably replaced by T 1 N T 1 N ? exposed in headwall scarp of large landslide complex Tolan, 1982; Tolan and Beeson, 1984). Hyaloclastite is 14 43 QUATERNARY 205 ft (40 and 60 m). Everywhere overlain by fine-grained unit includes local sand accumulations below 200 ft (60 m) some combination of smectite, hematite, carbonate, Qtdwl along Washougal River; well logs indicate flow is more well indurated, poorly sorted, and composed of 12 VOLCANIC ROCKS OF THE Missoula-flood deposits (Qfs) at elevations between 165 elevation, in part mapped as sand and silt deposits (Qs) by serpentine, quartz and kaolinite). Some flows also contain 21 than 120 m thick north of Nichols Hill. Weathered scoria subrounded to well-rounded, sand- to cobble-size clasts of BORING VOLCANIC FIELD and 245 ft (50 and 75 m). Locally capped at southern end Trimble (1963) phenocrysts of augite (<1 percent; 0.5 to 1 mm across) Pleistocene and ash cut by dike exposed in roadcut on north flank of brownish-yellow, partially palagonitized sideromelane 5050 of map area by <3 m of horizontally bedded feldspar- and (Tolan, 1982). Local foreset bedding and clast imbrication and microphenocrysts of Fe-Ti oxide. Groundmass Qmmn 683±9 ka Mount Norway, which presumably marks vent; Nichols 50 lithic-rich sand and angular andesite gravel supported by BASIN-FILL DEPOSITS consists of plagioclase, augite, Fe-Ti oxide, and minor to 50 Hill also composed of pyroclastic debris and is probably a indicate northwest transport direction. Lava flow is Tvs silt and sand matrix; inferred to represent lahar and lahar- abundant interstitial glass (largely devitrified or replaced 6 4 subsidiary vent. Overlies basaltic andesite of Bear Prairie plagioclase-microphyric and contains rare plagioclase Qa Qmpm QTc Unnamed conglomerate (Pleistocene and Pliocene?)- QTc runout deposits, probably from Mount Hood eruptions, and Qmbp crystals to 10 mm long in intergranular to intersertal by smectite, quartz, or calcite); groundmass textures 2 ( ). Chemically characterized by intermediate K2O Qtdwl 1.0 probably correlative to similar but thicker volcanogenic Unconsolidated to semiconsolidated, deeply weathered, chiefly intergranular to trachytic, less commonly subo- A Qtdwu 20 content (about 0.9 wt percent). Normal magnetic polarity groundmass of plagioclase, olivine, augite, Fe-Ti oxides, 710 000 FEET sequences south of map area (J.W. Vallance and J.E. pebbly to bouldery conglomerate; overlies lithologically phitic or microphyric. All flows in unit are tholeiitic, and Qbch 1,159±14 ka (J.T. Hagstrum, written commun., 2008); sample from and minor to abundant interstitial glass; vesicles typically (OREG.) similar but older conglomerate member of the Troutdale Qls O’Connor, unpub. mapping). Age uncertain, but lack of filled with yellow clay. Chemistry of flow and hyaloclas- many are exceptionally rich in Fe (FeO* as high as 13 wt. Formation (Ttfc); thick-bedded, poorly sorted to moder- roadcut directly northwest of Mount Norway gave an Tbem weathering at contact with overlying fine-grained 40 39 tite similar, resembling the Rosalia chemical type of Swan- percent) and poor in Sr (<300 ppm) compared to mafic BASIN-FILL DEPOSITS Qmbp ately well sorted, clast supported, commonly imbricated Ar/ Ar plateau age of 693±9 ka Missoula-flood silt (Qfs) indicates that, in part, the unit son and others (1979); distinguished from other Wanapum rocks elsewhere in southern Washington Cascade range Qtdwl Qmpm 50 closely pre-dates the 20–15 ka Missoula Floods; optically and crossbedded; includes thin lenses (<2 m thick) of Basaltic andesite of Pepper Mountain (Pleistocene)- (du Bray and others, 2006; Evarts, 2006a,b; Evarts and 49 15 Basalt flows by higher concentrations of TiO (3.6 wt 18 Tbem ? Qmbb 2 9 Qls Qls 5049 1,292±19 ka stimulated luminescence ages from correlative deposits basaltic and (rarely) quartzofeldspathic sand. Well- Weathered flow of platy, microvesicular, olivine-phyric to O’Connor, 2008; R.C. Evarts, unpub. data). Phillips and Ta Qfg Ttfh percent), P2O5 (0.8 wt percent), and FeO* (>14.5 wt Qls 2.0 south of the map area range from >155 ka to 22.4±2.5 ka. rounded to subrounded clasts as large as 50 cm across microphyric basaltic andesite that caps ridge south of others (1986) obtained K-Ar age of 27.9±1.9 Ma from Ta 5 8 percent). Reversed magnetic polarity (Swanson and others, Tbem Qls QTc derived mostly from Columbia River Basalt Group; sparse Howard Canyon; erupted from vent at Pepper Mountain, Qfs Qls Qbbv 2,284±16 ka Distribution and composition of unit indicate deposition 1979; Tolan, 1982; Tolan and Beeson, 1984). Age approxi- locality near stratigraphic top of unit just north of map 7 40 39 Qls Qls QTfg during Sandy River aggradational phase, likely in part clasts of volcanic rocks eroded from Cascade Range and about 6 km east of map area (R.C. Evarts and R.M. area; Ar/ Ar ages from unit to west and northwest of Qtdwl Ttfc mately 14.5 Ma (Tolan and others, 1989) 25 coinciding with late Wisconsin (30–20 ka) glaciation of quartzite also present. Typically more poorly sorted and Conrey, unpub. mapping); no more than 10 m thick. map area range from 27.1±0.1 Ma to 25.5 ± 0.2 Ma Qls 21 VOLCANIC ROCKS OF Qa Ttfc Mount Hood region and late last-glacial eruptive events at has more diverse clast population than underlying Trout- Consists of olivine phenocrysts and microphenocrysts Frenchman Springs Member—Most voluminous and (Evarts, 2006a,b; Evarts and O’Connor, 2008) Qtdwl ? ? HIGH CASCADE RANGE Qtdw Qfs widespread member of Wanapum Basalt (Tolan and l Qa 3.0 Local unconformity Mount Hood. Corresponds in part to the Estacada Forma- dale Formation conglomerate member, but general litho- (5–8 percent; to 1 mm across, a few as large as 2 mm 13 Qa Qa Qfg logic similarity of the two units makes contact difficult to across; commonly altered to clay; chromian spinel inclu- others, 1989). Three Frenchman Springs flows overlie Tlkt Pliocene tion as defined and mapped by Trimble (1963), but prob- Qa Qtdwl Grande Ronde Basalt near Corbett (Tolan, 1982) Qa Tbem Tbem ably older than the 14- to 12-ka Clackamas River gravel locate; inferred to be more than 60 m thick where exposed sions) and traces of plagioclase and clinopyroxene in Contact—Solid where location is accurate; long-dashed where Qtdwl Qfs Ttfh Twfs Qa QTc (Wampler, 2004) that composes the type section of the in landslide scarps on south side of Little Washougal fine-grained trachytic groundmass of plagioclase, clinopy- s Basalt of Sentinel Gap of Beeson and others (1985)- approximately located; short-dashed where inferred; Qa 5048 Estacada Formation. Equivalent to ancestral Sandy River River valley. Clast imbrication indicates transport to roxene, and Fe-Ti oxide. Calc-alkaline, with Mg# = Single thin (8 m) flow of hackly jointed, microphyric dotted where concealed Qtdwl 5048 northwest. Age uncertain but to west of map area overlies 62–67, K O = 1.0–1.2 wt percent; relatively high Ba Qa Qa Ttfc alluvium (Qaas) mapped in adjacent Camas quadrangle 2 basaltic andesite (52.4 wt percent SiO2); overlies basalt of Pliocene Qfg (Evarts and O’Connor, 2008) hyaloclastic sandstone member of Troutdale Formation (500–650 ppm), Sr (1,040–1,300 ppm), and Ba/Nb Sand Hollow on Corbett Hill Road about 0.5 km east of Fault—Long-dashed where approximately located; short- 35' L 35' and (or) AC (Ttfh) (Evarts and O’Connor, 2008) (50–80). Magnetic polarity unknown; sample collected 5 A QTc Tsr Miocene Qtds Corbett Station; overlain by hyaloclastic sandstone dashed where inferred; dotted where concealed; queried M 3 Terrace deposits 3 (Pleistocene)—Weathered and uncon- 40 39 A QTfg km east of map area yielded an Ar/ Ar age of 846±6 ka member of Troutdale Formation (Tolan, 1982). Contains S solidated sandy gravel underlying terraces and uplands Unnamed fan gravel (Pleistocene and Pliocene?)—Deeply where existence or extent uncertain. Ball and bar on (R.C. Evarts, unpub. mapping; R.J. Fleck, written along the Sandy River; forms deposits as thick as 35 m that weathered unconsolidated sand and cobbly gravel poorly sparse phenocrysts ≤1 mm long of plagioclase, brown downthrown side. Arrows show relative horizontal move- Unconformity commun., 2012) underlie dissected benches with surfaces as high as 540 ft exposed along Sandy River valley near southern boundary augite, and olivine in abundant opaque glass. Lithologic ment Qfg 52 (165 m) elevation. Composed of sandy bouldery cobble of quadrangle; underlies extensive northwest-sloping Qbch Basalt of Chamberlain Hill (Pleistocene)—Blocky- to characteristics, stratigraphic position, chemistry, and Qac BEDROCK piedmont surface south of the map area and west of Sandy columnar-jointed flow(s) of gray, diktytaxitic, tholeiitic normal magnetic polarity (Tolan, 1982; J.T, Hagstrum, Reverse fault—Dashed where inferred, dotted where Qa gravel in poorly sorted, clast-supported beds to 5 m thick Columbia River Basalt Group written commun., 2006) indicate this flow is a high-P O concealed. Sawteeth on upper plate with lenses of gray silty coarse sand. Some beds contain River. Clasts consist chiefly of andesite and other Cascade basalt (49.6–50.5 wt percent SiO2) exposed near Cham- 2 5 5047 14.5 variant of the informal basalt of Sentinel Gap of Beeson LA af af Qfg abundant subrounded clasts, as large as 1 m across, of Range rock types; weathering rinds on clasts exceed 1 cm berlain Hill, a cinder cone that marks the probable vent K Qac 5047 Twpr E r TERTIARY thick. Locally includes diamicts, interpreted as lahar and and others (1985, 1989), which is stratigraphically near the Strike and dip of beds Ttfc Mount Hood-derived hornblende andesite; other common (Treasher, 1942; Trimble, 1963; Allen, 1975); maximum lahar-runout deposits, that contain 1-m-diameter clasts of thickness about 60 m. Contains phenocrysts of olivine top of the Frenchman Springs Member Unconformity clast types include light-gray, olivine-phyric, Pliocene to Strike and dip of platy parting in lava flows af Pleistocene basaltic rocks, andesites eroded from the pyroxene and hornblende andesite. Capped by as much as (4–5 percent; 1 to 2 mm across; variably oxidized to Twfsh Basalt of Sand Hollow of Beeson and others (1985)- Twfs Qa s (25 m) of strongly oxidized and pedogenically altered iddingsite or an oxide phase; inclusions of chromian Blocky to columnar to hackly jointed, sparsely but Miocene Rhododendron Formation, and dark-gray to black aphyric af rocks of the Columbia River Basalt Group. Most clasts, micaceous silt, inferred to be loess (Qlo). Morphology spinel) and plagioclase (2–4 percent; 1–2 mm long) in coarsely plagioclase-phyric basaltic andesite (52.3–52.7 Strike and dip of eutaxitic structure in pumiceous tuff F 15.3 A Twfsh and composition of unit indicate deposition in broad fan holocrystalline intergranular groundmass of olivine, clino- wt percent SiO ); two flows, totaling 40 m thick, overlie U especially Mount Hood andesites in upper parts of expo- 2 L by an ancient Sandy River draining Cascade Range. pyroxene, plagioclase, and Fe-Ti oxide; troctolite clots Sample locality for chemical analysis—Showing map T Qls? 15.5 sures, are highly weathered and easily cut by shovel or Grande Ronde Basalt and underlie basalt of Sentinel Gap Tgsb broken by rock hammer, revealing weathering rinds Topographic position, degree of weathering, and thick common. Reversed magnetic polarity (J.T. Hagstrum, near Corbett Station and on slopes to east; flow exposed in number in table 1 Qac 40 39 50 several millimeters to 1 cm thick; sand matrix commonly overlying loess mantle imply substantial age, probably written commun., 2006). An Ar/ Ar plateau age of quarry at Corbett Station contains local zones of pillow 5046 Qac 46 Unconformity Sample locality for 40Ar/39Ar age determination—- Qa QTc leached to light-gray color. Basal contacts where exposed early Pleistocene. Lahar deposits derived from an ancient 1,159±14 ka was obtained from sample collected in rock lava and hyaloclastic breccia, is approximately 50 m thick, Showing age±1-σ error. See table 2 Volcanic and sedimentary rocks are strath surfaces on hyaloclastic sandstone member of volcanic center, possibly the Sandy Glacier volcano pit on Mershon Road and may be an intracanyon flow (Tolan, 1982; Tolan and Qac the Troutdale Formation (Ttfh) at elevations between 300 (Wise, 1969; Sherrod and Scott, 1995) located in the Qmbp Basaltic andesite of Bear Prairie (Pleistocene)—One or others, 1984). Basalt of Sand Hollow flows, capped by a A (BRIDAL VEIL) Sample Locality for luminescence age—Showing map letter Qh 2 Tt and 350 ft (90 and 105 m). Locally capped by loess (Qlo) Mount Hood area. Mapped as Springwater Formation by more flows of light- to dark-gray, columnar-jointed, thick paleosol, also crop out in the headwall of the Rooster Qa in table 3 and fine-grained Missoula-flood deposits (Qfs). Distribu- Trimble (1963), but geomorphic relations outside the map porphyritic, calc-alkaline basaltic andesite (52.5–53 wt Rock landslide. Distinguished by scattered large (to 3.5 cm Tvs Tob Ta Oligocene tion and composition of unit indicate deposition during a area indicate that it is probably younger than deposits in across) phenocrysts and glomerocrysts of amber plagio- Qac Qac percent SiO2) that underlie area west-northwest of Mount 5 (CAMAS) Sample locality for radiocarbon age—Showing map number major aggradational episode in the ancestral Sandy River, the type area near Springwater, about 30 km south of map Norway; thickness in map area between 25 and 50 m (80 clase; groundmass typically microphyric, intersertal to 27.0 Tbem area in table 4 Qa probably in conjunction with glaciation of the Mount and 160 ft). Erupted from vents marked by cinder cones in intergranular, composed of plagioclase, brown augite, Hood region; concentrations of Mount Hood andesite Troutdale Formation (Pliocene and Miocene?)-Semi- Larch Mountain quadrangle to north (Trimble, 1963; Fe-Ti oxide, olivine (partly altered to clay), and red-brown Cinder cone 50 Qh boulders and gray silty sands may reflect deposition, in interstitial glass; microvesicles typically filled with 45 Qa consolidated to well-consolidated conglomerate and sand- Allen, 1975; Hammond and Korosec, 1983; R.C. Evarts, 13 Qac 5045 part by lahars, associated with eruptive activity. Age stone. Divided into two informal members that, in the unpub mapping); subsequent incision by Washougal yellow-brown isotropic clay or calcite. Stratigraphic Qac uncertain, but probably much greater than 100 ka judging map area, are typically separated by an erosional uncon- River has separated flows in map area from source area. position, chemistry, petrography, and normal magnetic Qh DESCRIPTION OF MAP UNITS Deposits derived from the Mount Hood volcano from weathering and geomorphic position. Luminescence formity Flows contain olivine phenocrysts (about 6 percent; 1 to 2 polarity (Tolan, 1982; J.T. Hagstrum, written commun., (Holocene)—Unconsolidated, stratified sand and gravel analysis on sand near the base of the unit in the southern 2008) indicate correlation with informal basalt of Sand Qe Qac Ttfh Hyaloclastic sandstone member (Pliocene)—Fluvial mm across; variably oxidized; inclusions of chromian SURFICIAL DEPOSITS and diamictons composed of volcanic debris transported part of the map area indicates some of these deposits are Hollow of Beeson and others (1985), erupted approxi- sedimentary strata distinguished by indurated, coarse sand- spinel) in trachytic groundmass of plagioclase, clinopy- Qac down Sandy River from Mount Hood; underlie an exten- older than 220 ka. Corresponds in part to the Gresham mately 15 Ma (Beeson and others, 1985; Barry and others, Qh stone composed of abundant grains of glassy, roxene, olivine, Fe-Ti oxide, and minor interstitial glass. af 9 af Artificial fill (Holocene)—Unconsolidated soil, sand, gravel, sive lowland north of Broughton Bluff informally known Formation as defined and mapped by Trimble (1963) 2010) olivine+plagioclase-phyric basalt and conglomerate that Overlies conglomerate and sandstone mapped as Trout- 5 Qe and crushed rock used for highway and railroad beds, as the Sandy River delta. As thick as 25 m in lower Sandy Qe Qe Washougal River terrace deposits (Holocene and contains olivine-bearing basalt clasts; well exposed on dale Formation; overlain by basaltic andesite of Mount levees, and small dams River valley (Pierson and others, 2009) and 9 m in Sandy Norway. Reversed magnetic polarity (J.T. Hagstrum, Grande Ronde Basalt (Miocene)—Light-gray to black flows 10 Pleistocene)—Fluvial gravel and sand forming terraces Crown Point Highway and along Sandy River, where it 5044 Qe River delta where locally interbedded with Columbia written commun., 2001); sample collected from upper of tholeiitic basaltic andesite; vesicular to microvesicular, 7 12 Eolian deposits (Holocene)—Unconsolidated, well-sorted in valleys of Washougal and Little Washougal Rivers overlies and intertongues with micaceous arkosic sand- River overbank deposits and almost everywhere overlain flow in adjacent Larch Mountain quadrangle gave aphyric to microphyric to very sparsely plagioclase- 11 sand forming small dunes cresting as high as 5 m above stone, siltstone, and claystone of the Sandy River Mud- by as much as 1 m of more recent Columbia River flood- Qtdwl Terrace deposits of lower Washougal River (Holocene 40 39 phyric; exhibit relatively low-TiO contents characteristic 6 Qh Qac adjacent floodplain level along Columbia River. Com- Ar/ Ar plateau age of 1,220±8 ka (R.J. Fleck, written 2 Qac and Pleistocene)—Unconsolidated sandy gravel and sand stone (Tsr). Hyaloclastic sandstone (equivalent to vitric posed of fine to coarse, micaceous quartzofeldspathic plain deposits (Rapp, 2005). Sand and gravel form planar commun., 2012) of the Grande Ronde Basalt of the Columbia River Basalt or cross-stratified beds that typically fine upwards; gray underlying small terraces, with elevations between 50 and sandstone of Trimble (1963) and Tolan and Beeson (1984)) Group (Swanson and others, 1979; Mangan and others, 8 BLUE Qac sand of Columbia River provenance. Position on Colum- Qmbb except for fine sand beds, which are locally red to pinkish. 130 ft (15 and 40 m) along lower Washougal River; gener- consists largely to entirely of angular to subrounded Basaltic andesite of Broughton Bluff (Pleistocene)—Two 1986; Beeson and others, 1989; Reidel and others, 1989). Qe bia River floodplain deposits indicates dunes less than 122 22'30" 122 15'00" LAKE Qe Gravel clasts are dominantly fresh, porphyritic, pyroxene ally <10 m thick. Gravel is poorly sorted, locally imbri- fragments, 2 to 6 mm across, of black, generally nonve- flows of gray, columnar-jointed, calc-alkaline basaltic Flows in this quadrangle generally display blocky to Qac 2–3 ky old. Historically active but now mostly vegetated sicular basalt that contains phenocrysts of olivine (0.5–2 andesite (52–53 wt percent SiO ) that underlie upland area LACAMAS LARCH MOUNTAIN QUAD. Qac FAULT Qls and hornblende andesites; sand composed mostly of angu- cated, and varies from compact with sand matrix to loose 2 columnar jointing patterns and vesicular flow tops; pillow CREEK Creek Twfsh Ta and stable owing to circa 1940s diminishment of sand Qac Qac Qac mm) and plagioclase (1–3 mm) in a glassy (sideromelane) west of Chamberlain Hill, the presumed vent (Treasher, QUAD. Qt Qac Qt Qh 22 16 lar to sub-rounded, gray to red lithic (andesite) fragments, openwork texture. Clasts subangular to well rounded, lava locally present at base. Typical samples are inter- 45 37'30" Ttfh Qls Qac af supply from beaches and sand bars flanking Columbia Little 32' 30" Ttfh Qh Qac 26 21 Tgsb 32'30" derived from Tertiary volcanic and granitic rocks of to intergranular groundmass; sideromelane partly to com- 1942; Trimble, 1963; Allen, 1975); forms discontinuous BRIDAL af 31 5–20 percent clear plagioclase fragments, and 2–10 granular to intersertal, with lathlike plagioclase, granular Winkler Qls 3 23 River that were more frequently exposed prior to flow VEIL 24 50 pletely altered to palagonite, which cements sandstone and cliff extending east and southeast of Broughton Bluff; as 5043 45 14 Qlo Twfsh Qa 43 percent equant hornblende crystals. Diamictons are brown Cascade Range, Columbia River Basalt Group, and Trout- clinopyroxene, and Fe-Ti oxide crystals in abundant dark CAMAS QUAD. 1.53±0.39 Ma 46 Qls Qh Qls Twfs Qls 32 regulation Washougal RIVER 25 h Twpr imparts a distinctive yellowish-brown color to the origi- thick as 60 m. Contains phenocrysts of olivine (to 9 QUAD. 48 Qh 33 r to brownish gray, massive to weakly stratified beds, 0.5 to dale Formation. Deposits minimally weathered; inferred glass; some flows contain rare plagioclase phenocrysts to Mount 1,292±19 ka 47 Qac 140 Norway 29 Alluvium of Columbia River floodplain and channel 5 m thick, composed of 30–50 percent angular andesite to represent aggradation behind former blockage by nally dark green rock; many beds contain minor admixed percent; mostly 0.5 to 1 mm but a few as large as 3 mm 15 mm long; textures resemble those described by Long Qh 49 Ttfh Twfsh Twfsh Qmbb 52 Twfss 34 B' (Holocene)—Unconsolidated fine sand, silt, and clay that nonvolcanic debris such as quartz, muscovite, hornblende, across; inclusions of chromian spinel; locally replaced by Ttfh Qlo 30 fragments to 10 cm diameter in matrix of sand, silt, clay, coarse-grained Missoula-flood bar (Qfg) that now and Wood (1986) for correlative flows in the Columbia River Qt 53 Qls Twprr and potassium feldspar. Sandstone ranges from poorly iddingsite) in a trachytic to subophitic groundmass of Nichols Qls underlies historic floodplain, islands, and bars of the and wood (Rapp, 2005). Numerous radiocarbon ages and constricts mouth of Washougal River Basin. Based on field, chemical, and paleomagnetic prop- Hill 15 Twfss Ttfh Twfss Columbia River at elevations less than 30 ft (10 m); com- sorted to well sorted; typically thick-bedded, commonly plagioclase, augite, and Fe-Ti oxide. Reversed magnetic Qa Ttfh Ttfh 27 regional stratigraphic relations show that these deposits Qtdw Terrace deposits of upper Washougal River erties, Grande Ronde Basalt flows in map area are Qa Twfsh u lenticular, crossbedded, and contains dispersed pebbles 28 posed largely of quartz, feldspar, and conspicuous musco- are younger than 1,600 years old. Stratified sand and polarity (J.T. Hagstrum, written commun., 2003). An assigned to the Sentinel Bluffs Member (Reidel and Woodburn Qlo (Pleistocene)—Unconsolidated to weakly consolidated 40 39 Ttfh vite. Near tributary mouths, unit includes rare lenses of and cobbles of olivine-bearing basalt. Interbedded Ar/ Ar age of 1,292±19 ka was obtained from a sample Hill WASHOUGAL Creek gravel interpreted to represent fluvial aggradation cobbly gravel and sand forming terraces along Washougal others, 1989; Reidel, 2005) within the N2 magnetostrati- Twfsh cobble to pebble gravel composed largely of well- conglomerate mostly well sorted and clast supported; collected near west edge of the map area, consistent with Qh Qmbb Twfsh triggered by highly increased sediment supply following River north and northeast of Mount Norway; tread eleva- graphic unit of Swanson and others (1979), which was Creek consists of well-rounded to subrounded pebbles and K-Ar age of 1.53±0.39 Ma reported by Conrey and others Campen Qls rounded clasts reworked from Troutdale Formation; also Mount Hood eruptions. Diamicts are interpreted as depos- emplaced about 15.5 Ma (Barry and others, 2010) CAMAS Qlo Qlo 36 tions between 190 and 310 ft (60 and 95 m); generally less Creek 5042 Qbch includes local unmapped areas of dredge spoils and other cobbles of variably vesicular, olivine+plagioclase-phyric (1996a) its of Mount Hood lahars produced in conjunction with than 5 m thick. Poorly to moderately well sorted and Tgsb Sentinel Bluffs Member—Uppermost member of the WASHOUGAL Gibbons Tlkt Ttfh 50 basalt, basaltic rocks of Columbia River Basalt Group, and B 42 fills, and possibly eolian deposits. Sections exposed in eruptive activity. Deposits were chiefly formed during and QbbvQbch Basalt of Bridal Veil Creek (Pleistocene)—Single basalt imbricated, with matrix of coarse sand. Clasts as large as Grande Ronde Basalt (Reidel, 2005; Reidel and Tolan, in Walton banks, excavations, and drill-core samples commonly generally minor amounts of quartzite and other rock types; Creek after the Timberline and Old Maid eruptive episodes of 50 cm across, well rounded to subrounded, composed of (50.1–50.4 wt percent SiO2) flow with well-developed Ttfh show sand-silt couplets as thick as 30 cm; basal sands some conglomerate beds poorly sorted, with subangular press). Flows distinguished by relatively high MgO 14 Qtds 44 50 Crandell (1980); diamictons and stratified sands older colonnade and entablature that caps narrow ridge north of COLUMBIA 1 Cascade-derived volcanic and granitic rocks. Age uncer- contents (4.5–5.0 wt percent MgO) and normal magnetic MULTNOMAH CO Qh 1,159±14 ka locally display ripple cross lamination, planar lamination, basalt boulders as large as 1 m across. Angular nonvesicu- CLARK CO Ttfh 51 than 800 years are related to the Timberline period, which tain but absence of weathering rinds indicates late Quater- Howard Canyon; about 30 m thick; flowed into map area Lawton Qls and tabular foresets; capping silt and clay beds generally lar vitric clasts in hyaloclastic sandstone beds interpreted polarity (Reidel and others, 1989; Reidel, 2005). Three Ttfh began about A.D. 400 (Rapp, 2005; Pierson and others, nary age. Found within reach of river flanked by large from east (R.C. Evarts, unpub. mapping). Contains olivine massive and bioturbated; couplets interpreted as deposits as debris generated by basalt-water interaction in the Sentinel Bluffs flows, totaling at least 50 m thick, crop out Qa 2009). Timberline-age deposits underlie much of the landslide complexes; probably formed during short-lived phenocrysts (7–8 percent; to 5 mm across; iddingsite Ttfh of large Columbia River floods before substantial 20th Columbia Gorge that was rapidly transported downstream in cliffs above Interstate 84 between Corbett Station and Gary I. Sandy River delta and aggraded the lower Sandy River periods of aggradation behind stream-blocking landslides rims; chromian spinel inclusions) in relatively coarse- Tunnel Point (Tolan, 1982); both are assigned to the basalt Qlo century river regulation and floodplain diking. Unit and deposited in eastern Portland Basin (Trimble, 1963; Reed Ttfh valley within the map area by as much as 25 m (Pierson grained, holocrystalline, intergranular to trachytic ground- Island Qtdl Terrace deposits of Little Washougal River of McCoy Canyon of Reidel (2005), which is found near WASHINGTON includes local diatomaceous beds and layers of organic- and others, 2009). Post-A.D. 1780 (Pringle and others, Swanson, 1986, 1988). Vitric clasts and associated basalt mass of plagioclase, olivine, greenish-brown clinopyrox- Flag RIVER Qh the base of the Sentinel Bluffs Member OREGON 5041 Ttfh Tlkt rich sediment that probably formed in floodplain (Pleistocene)—Unconsolidated, little-weathered gravel cobbles exhibit a low-potassium-tholeiite composition Island Ttfh Ttfh 2002; Pierson and others, 2010) Old Maid-age deposits ene, and Fe-Ti oxide; most samples contain traces phlogo- Ttfh 5041 and sand flanking Little Washougal River; as much as 5 m Ttfh marshes, ponds, and lakes, as well as thin (<2 cm) tephra form stratified sand and gravel aggradation sequences as (Swanson, 1986, 1988; Lite, 1992; A.W. Sarna-Wojcicki, pite in groundmass interstices or in vesicles. Overlies Crown S thick. Gravel is poorly sorted, composed of subangular to written commun, 2005), indicating probable derivation VOLCANIC AND SEDIMENTARY ROCKS Broughton Point A Qlo beds from Holocene eruptions of Mount St. Helens. thick as 23 m in the Sandy River valley, overtopping and hyaloclastic sandstone member of the Troutdale Forma- 30 Chanticleer N Qtds3 Bluff 84 Hwy T 1 N These deposits resulted from river aggradation since the well-rounded clasts derived from Tertiary volcanic and from compositionally similar middle Pliocene basalt flows Point D burying much of the Timberline-age deposits; they also tion Reversed magnetic polarity (J.T. Hagstrum, written Tt Tuff (Oligocene)—Olive-green, moderately welded, Chamberlain River Y 38 granitic rocks of Cascade Range, Columbia River Basalt Corbett T 1 S Qtds2 last glacial sea-level low stand at about 15 ka (Baker, form several channel-fill deposits, as thick as 5 m, in the east of map area (Swanson, 1986, 1988; R.C. Evarts and commun., 2005); 40Ar/39Ar plateau age is 2,284±16 ka Hill Qfs 2 Qbbv 680 000 FEET (OREG.) plagioclase-phyric, pumiceous lapilli tuff. Exposure TROUTDALE Pounder 2002); locally extends to 300 ft (90 m) below sea level in Group, and Troutdale Formation. Inferred to record aggra- R.M. Conrey, unpub. mapping) Columbia Qfs Sandy River delta (Rapp, 2005) beneath landslide debris on shore of Washougal River, Qa Qtds2 4 37 dation behind landslides that temporarily blocked river Qa 3 Qh 2,284±16 ka the map area (Hoffstetter, 1984; Hartford and McFarland, Ttfc Conglomerate member (Pliocene and (or) Miocene)- VOLCANIC ROCKS OF THE THE HIGH CASCADE RANGE Qlo Loess (Holocene and (or) Pleistocene)—Massive unconsoli- about 1 km northeast of Mount Norway, is porphyritic, Creek 1989; Gates, 1994; Pratt and others, 2001; Rapp, 2005). Cataclysmic-flood deposits (Pleistocene)—Sediment depos- Consolidated, well sorted, clast-supported, pebble and Springdale Qa Qa dated deposits of light-gray to buff, micaceous, quartz- composed of euhedral to embayed phenocrysts of plagio- Qa Consistent with this, in the adjacent Camas quadrangle, ited by colossal glacier-outburst floods caused by cobble conglomerate composed largely of well-rounded QbchTlkt Low-potassium tholeiite (Pliocene)—Medium- to dark-gray, Historic Qh Qa Ttfh feldspathic eolian silt and fine sand; commonly contains clase (approximately 20 percent; about 1–2 mm across; Smith alluvium of the Columbia River contains fluvially coarse-grained basalt (49.2 wt percent SiO ) overlying Creek Howard Qh Ttfh repeated failure of ice dam at Clark Fork that formed clasts of Columbia River Basalt Group with minor but 2 locally replaced by albite, calcite, smectite) and small SANDY 5040 Qh Qa isolated granules and small pebbles; locally capped with R concentrated 7.7-ka Mazama tephra (Gates, 1994) at 45 ft Pleistocene Lake Missoula in western Montana (Bretz, hyaloclastic sandstone member of the Troutdale Forma- Canyon Qa persistent quartzite and granitic and felsic metamorphic Beaver I 5040 strongly developed red soils, especially on higher uplands. grains of pyroxene in zeolitic, originally glassy matrix V (14 m) below sea level. Regionally, most deposits above Creek E 1925, 1959; Bretz and others, 1956; Trimble, 1963; rocks; sparse interbeds of volcanic lithic and micaceous tion. Approximately 12-m-thick flow exposed in headwall Qtds2 Forms widespread mantle to 25 m thick on upland south with well-preserved shard texture; about 5–10 percent Big af R Tlkt modern low-water river level (3 ft (1 m) above sea level RIVER Allison, 1978; Baker and Bunker, 1985; Waitt, 1985, quartzofeldspathic sandstones; mapped only north of scarp of landslide between Chanticleer Point and Crown angular lithic clasts, mostly porphyritic volcanic rocks. Ttfh 35 Qls in map area) are younger than 2,000 years old and most of Columbia River. Less-weathered accumulations mantle 45 30'00" 1994, 1996; Atwater, 1986; O’Connor and Baker, 1992; Columbia River but some conglomerate mapped as Ttfh Point (Williams, 1916; Lowry and Baldwin, 1952; SANDY QUAD. 70 000 FEET Qfs flatter surfaces along south side of Columbia River valley Outcrop in landslide scarp northwest of Mount Norway is Creek Qtds2 dated deposits forming Reed Island are less than 500 Benito and O’Connor, 2003). Largest floods achieved Waters, 1973; Tolan and Beeson, 1984); isolated outcrop Creek (WASH.) Ttfh near Corbett Station. Overlies 970-ka basaltic andesite of south of river, especially west of Chanticleer Point, may similar but highly weathered Gordon Buck Creek F years old Qtds2 Ttfh A stages of 400 to 500 ft (120 to 150 m) as they spread and actually belong to this unit. Intensely weathered to depths south of Cemetary Hill is erosional remnant of a different U Qh Ttfh Broughton Bluff (Qmbb); probably deposited during L Qtds3 slowed over the eastern Portland Basin after exiting the flow judging from slightly different paleomagnetic orien- Tvs T Qa Alluvium (Holocene and Pleistocene)—Unconsolidated of several meters. Well logs indicate unit is more than 200 Volcaniclastic sedimentary rocks (Oligocene)—Thin Qtds2 Ttfh Tlkt several episodes throughout late Quaternary time; Qmpm western Columbia River Gorge with velocities of 35 m/s tation (J.T. Hagstrum, written commun., 2005) and is Index map showing geographic and cultural features of the Washougal 7.5' quadrangle sand, gravel, and organic-rich mud along rivers and includes Holocene accumulations closer to the Columbia m thick east of Campen Creek. Equivalent in part to upper discontinuous lenses of volcaniclastic rocks interbedded Qls Tsr at peak discharge (Benito and O’Connor, 2003). Depos- member of Troutdale Formation of Mundorff (1964) and to probable distal end of poorly exposed flow(s) that under- with and overlying basaltic andesite flows (Tbem) along and vicinity on hillshade image derived from 10-m DEM. Qa creeks and in seasonally inundated depressions. Deposits River along Washougal, Little Washougal, and Sandy Rivers ited coarse traction load in series of large bars and plains, lower member of Troutdale Formation of Tolan and lie ridge south of Howard Canyon. Diktytaxitic, com- Washougal River. Primarily light-green to dark-brown, 5039C Qfs QTfg Ttfh Sandy River terrace deposits (Holocene and chiefly west of map area and including Portland delta of Beeson (1984). Late Miocene to early Pliocene age monly vesicular, with vesicle cylinders/segregation veins; Qa Qtds3 5039000mN consist mostly of st ratified sand and cobble to pebble poorly sorted, lithic lapilli tuff and tuff breccia probably Ttfh Pleistocene)—Fluvial gravel and sand forming sets of Bretz (1925). Downstream constrictions temporarily inferred from stratigraphic relations outside of quadrangle intergranular to subophitic textures; composed of plagio- Qlo Qa gravel; deposits along smaller watercourses are more deposited by lahars; pervasively altered to smectite, terraces in Sandy River valley; include Mount Hood lahar ponded floodwater in Portland Basin, promoting deposi- clase (0.5–1 mm long; variably altered to kaolinite), Ttfh variable. Known thicknesses everywhere less than 10 m. (Trimble, 1963; Tolan and Beeson, 1984) kaolinite, and zeolites Qa Qh Qh Tlkt Holocene alluvium along the Sandy River post-dates late deposits. Divided into three units based on differences in tion (Trimble, 1963). Radiocarbon and tephrochronologic olivine (0.5–1 mm across; variably altered to iddingsite; 1 Qa Qa Ttfh A Tsr Sandy River Mudstone (Pliocene and Miocene)- Qh Ttfh Tsr tread elevations and weathering characteristics data from outside map area indicate depositional ages of chromian-spinel inclusions), augite (0.5 mm across), Ta Andesite (Oligocene)—Scattered flows of sparsely to abun- 45o30' o 18th-century Old Maid eruptive period from Mount Hood Semiconsolidated, well-bedded sandstone, siltstone, 1 520 000 FEET (WASH.) 1 550 000 FEET (OREG.) o 45 30' o 550 551 552 20' 553 (SANDY) 554 555 17'30" 556 557 122 15'' (BULL RUN) Qh Qtds 20 to 15 ka (Waitt, 1985, 1994; Atwater, 1986; Benito Fe-Ti oxide, and interstitial glass. Chemically distin- dantly porphyritic to seriate pyroxene andesite. Contain 122 22'30" 558000mE (included in ) 1 Terrace deposits 1 (Holocene and Pleistocene)—Poorly claystone, and minor quartzite-bearing conglomerate,

R3E R4E and O’Connor, 2003; Clague and others, 2003; O’Connor guished by low K O (0.1–0.3 wt percent) content. Most phenocrysts of plagioclase (3–20 percent; as long as 3 15.5° Qt exposed, unconsolidated, sandy cobble to boulder gravel to pumice-lapilli tuff, and lignite; crops out along Sandy 2 Base from U.S. Geological Survey, Washougal, WA-OR, 1994 SCALE 1:24 000 Geology mapped by T.L. Tolan, 1980–1981; Talus deposits (Holocene and Pleistocene)—Unsorted accu- R.C. Evarts, 1999, 2002-2011; and J.E. 20 m thick underlying terrace surfaces at elevations and Benito, 2009). Coarse bedload deposits and fine outcrops moderately to severely weathered. Normal mag- mm), clinopyroxene (0.5–1 percent; as large as 2 mm (DAMASCUS) 1 1/2 0 1 MILE mulations of large angular basalt blocks below cliffs River at south edge of map area (Trimble, 1963). Thick- North American Datum of 1927 (NAD27). Projection: O'Connor, 2003-2007; assisted by P.A. slack-water deposits mapped separately netic polarity (J.T. Hagstrum, written commun., 2005). across), orthopyroxene (0.3–5.5 percent; to 2 mm long; Qmmn Qmbb between 160 and 190 ft (50 and 60 m) along Sandy River. ness highly variable due to lateral gradations to gravel and Washington Coordinate System, south zone (Lambert conformal conic) 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET WASHINGTON Dinterman, 2002 composed of Quaternary lava flows ( and ) 40 39 Consist of subhorizontal gravel sheets, 0.5 to 5 m thick, Qfs Sand and silt facies—Unconsolidated light-brown to light- K-Ar and Ar/ Ar ages between 3.0 and 3.6 Ma were partially replaced by smectite), Fe-Ti oxide (0–1.4 10 000-foot ticks: Washington Coordinate System, south zone and Oregon GIS database and digital cartography by north of Mount Norway and near Broughton Bluff; to erosion; well logs show unit thicknesses less than 65 m 1 .5 0 1 KILOMETER locally separated by thin sand lenses; poorly sorted, locally obtained from correlative flows to east of map area percent) in pilotaxitic groundmass; small amounts of Coordinate Systen, north zone TRUE NORTH Karen L. Wheeler and Michael.G. Sawlan include post-landslide rockfall deposits at base of head- gray silt, clay, and fine to medium sand. As much as 20 m in Sandy River area (Swanson and others, 1993) but more MAGNETIC NORTH imbricated, and varies from compact clast-supported (Conrey and others, 1996b; R.J. Fleck, written commun., olivine phenocrysts (about 0.5 mm across; altered to Blue 1000-meter Universal Transverse Mercator ticks, zone 10 OREGON wall scarps thick at low elevations in the region but thins toward than 150 m thick where buried beneath volcanic rocks and APPROXIMATE MEAN CONTOUR INTERVAL 20 FEET Edited by J. L. Zigler 2011) smectite) present in some flows; interstitial glass gener- DECLINATION, 2013 cobble and boulder gravel with sand matrix to loose open- upper mappable extent at 400 ft (120 m) elevation in map landslide debris in northern part of map area; may be Manuscript approved for publication Qls Landslide deposits (Holocene and Pleistocene)—Diamicts ally altered to smectite. In Washington, overlies and April 26, 2013 work cobble gravel; subangular to well-rounded clasts area. Upper map limit only approximately placed on basis more than 300 m thick in Camas quadrangle to west of unsorted, angular bedrock and surficial material trans- BEDROCK interbedded with basaltic andesite of Elkhorn Mountain MAP LOCATION include common large (to 1 m diameter) boulders of horn- of topography owing to difficulty in distinguishing unit (Hartford and McFarland, 1989; Swanson and others, ported downslope en masse. Chiefly deep-seated, semi- Tbem Tt blende andesite. Deposit contains at least one 1-m-thick from similar loess and clayey soils that cover most upland ( ) and overlain by lapilli tuff ( ); outcrop of platy coherent slumps and internally disrupted rockslide, earth- 1993). Sandy and silty beds are bluish gray in fresh expo- bed of silty lithic-rich sand inferred to be the distal facies of surfaces. Poorly exposed, but rare fresh exposures show COLUMBIA RIVER BASALT GROUP pyroxene andesite near Onion Rock is only occurrence of flow, and debris-flow deposits. Many mapped slides head sures, but more typical weathered exposures are light a Mount Hood lahar. Exhibits weakly developed soil multiple, 0.25- to 1.5-m-thick, fining-upward sequences pre-Grande Ronde Basalt rocks in map area south of at arcuate scars and exhibit subhorizontal tops, bulbous brown and commonly limonite-cemented. Consist of Wanapum Basalt (Miocene)—Dark gray to black, variably A A' profile and weathering rinds on fine-grain volcanic clasts of ripple cross-stratified, very fine sand grading up to Columbia River toes, and hummocky, poorly drained surfaces. Large subangular grains of quartz, feldspar, various rock vesicular to microvesicular, aphyric to sparsely phyric <1 mm thick, suggesting relative youth. Not covered by massive bioturbated clayey silt. Sand composed of quartz, fragments, muscovite, and minor biotite, tourmaline, mag- FEET Tob C-C' landslide complexes developed along Washougal River lava flows of high-TiO tholeiitic basalt and basaltic Olivine Basalt (Oligocene)—Isolated flow of dark-gray, Missoula-flood deposits so must postdate 20- to 15-ka feldspar, and conspicuous mica, indicative of a Columbia netite, hornblende. Thin claystone beds varicolored, com- 2 1,500 SECTION 1,500 and east of Chanticleer Point where Pliocene and Quater- andesite; exhibit blocky to columnar or hackly jointing coarse-grained, seriate, olivine- and plagioclase-phyric cataclysmic flooding. Thermoluminescence analysis on the River provenance. Coarser sand facies contain abundant Mount Norway nary lava flows overlie deeply weathered Troutdale monly carbonaceous, and locally tuffaceous. Planar and patterns and vesicular flow tops; upper few meters locally basalt exposed on south valley wall of Washougal River lithic-rich sand gave an age of 14.3±1.2 ka, consistent with dark volcanic rock fragments. Interpreted as slack-water Formation or Columbia River Basalt Group trough crossbeds and cut-and-fill structures within sandy thoroughly weathered to red saprolite or laterite. Textures about 2 km northwest of Mount Norway. Contains deposition after the Missoula floods. Presence may reflect sediment settled from temporarily ponded floodwater. 1,000 1,000 horizons indicate a fluvial depositional environment. Age resemble those described by Long and Wood (1986) for phenocrysts and glomerocrysts of blocky plagioclase (24 Qmmn Qt QTc Qls QTc 500 500

WASHOUGAL RIVER WASHOUGAL WASHOUGAL RIVER WASHOUGAL Ttfc Tsr Qa Qls Qtdwu

Tbem Qtdwl Tbem Tbem SEA LEVEL SEA LEVEL Tbem C C'

FEET 500 500 A-A'

1,500 SECTION 1,500 B-B'

1,000 feet = 305 meters SECTION VERTICAL EXAGGERATION X 2 Nichols Hill Relative movement - , toward viewer; , away from viewer Thickness of surficial units exaggerated 1,000 1,000 Chamberlain Hill Qmmn B B' QTc Qt Qlo Qmbb Qbch FEET Qbch Qls 1,500 1,500 500 Qbch Tsr 500 C-C' OREGON Qtds3 RIVER WASHOUGAL

Qfs SANDY RIVER SECTION Gibbons Creek Qa

WASHINGTON Ttfc Qfs Ttfh Qls Qtds Qls 2 Reed Island Qfg Qh Qh COLUMBIA RIVER Qac Qac Ttfc Tbem 1,000 Chanticleer Point 1,000 QTfg Chamberlain Hill SEA LEVEL Ttfh Qac SEA LEVEL Twfs Qlo Qbch Qlo s Tbem? Ttfh Ttfh Qlo Qlo Qlo Qls 500 Qmbb Qlo Qlo Ttfh 500 500 500 Twprr Ttfh Ttfh Twfsh SANDY RIVER Twfsh Qtds3 Qls Tgsb Qls 1,000 feet = 305 meters VERTICAL EXAGGERATION X 2 Qh Ttfh Ttfh Tgsb Twfsh Relative movement - , toward viewer; , away from viewer SEA LEVEL SEA LEVEL Tgsb Ta Ta Thickness of surficial units exaggerated Twfsh Artificial fill (unit af) too thin to portray on cross section

500 500

1,000 feet = 305 meters VERTICAL EXAGGERATION X 2 Relative movement - , toward viewer; , away from viewer Thickness of surficial units exaggerated

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Geologic Map of the Washougal Quadrangle, Clark County, Washington, and Multnomah County, Oregon This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters 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. By For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS Russell C. Evarts1, Jim E. O’Connor1, and Terry L. Tolan2 Digital files available at http://pubs.usgs.gov/sim/3257/ Suggested Citation: Evarts, R.C., O’Connor, J.E., and Tolan, T.L., 2013, Geologic map of the Washougal 1 2 quadrangle, Clark County, Washington, and Multnomah County, Oregon: U.S. Geological Survey U.S. Geological Survey, Groundwater Solutions, Inc. 2013 Scientific Investigations Map 3257, scale 1:24,000 [http://pubs.usgs.gov/sim/3257/].