U.S. DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 156
U.S. GEOLOGICAL SURVEY PLATE 2A
123°00'
{ CORRELATION OF MAP UNITS
Qls SEDIMENTARY AND VOLCANIC ROCKS AND DEPOSITS INTRUSIVE ROCKS
z 4 Inferred contact
als }) os F yn or Southern Willamette Valley (part) Cascade Range Foothills (part) Cascade Range Foothills (part
a) bas Peay neces nee Inlereoy a oceat ee Uneniet Ot ae ee and Coast Range and Souther Willamette Valley (part) and Northem Willamette Vales pet) All Areas
<i) si tive movement; T, movement toward viewer; A, movement away
Tms I from viewer (aferval lenatts Ons | als ‘One |_ Gls. Holocene
@ © 8 © © Concealed fault—Dots grouped where location is unconstrained; bar and QUATERNARY
Tims: Fa ball on downthrown side; queried where uncertain at at at Pleistocene
Strike and dip of beds
= QTb QTb
—+>- Strike and dip of overturned beds Pliocene
—+ _ Strike of vertical beds nae ee a
Tsau | Tsat | Tsaa Tsau | Tsat | Tsav | Tsaa
® Horizontal beds To tent qo Ltewt ee Miocene
Anticline—Showing plunge; dashed where approximately located, dotted Tegr Tegr
15! where concealed URS aE Tibal TBS
46°15! <4 Syncline—Showing plunge; dashed where approximately located; dotted TIb | tibw Tsm | Tmo Tb Tsm ‘Tmo
where concealed ae 2.
44 Monocline—Showing plunge; dashed where inferred : ‘Olaeeene
—— — — Aeromagnetic high—Contours enclose areas of high total intensity corre- Tms Tims Tbe | TF ms a
sponding in most places to intrusive bodies mapped or inferred at the
surface or in the shallow subsurface TERTIARY.
—0— Structure contour—Drawn on the base of the Eugene Formation in the Tsu
southern Willamette Valley south of Franklin Butte and Rogers Moun- ah ess are
tain and south and west of Salem Hills (contour interval 200 m) and Tet}
on top of the Columbia River Basalt Group in the northern Wil- i Tym
lamette Valley (contour interval 100 m); dashed where inferred Y tyim Tbs |) Twh
seneee2== | ocation of seismic reflection profile Tyv Eocene
RICHFIELD Barber 1 Subcrop (concealed contact) of Eugene Formation (not shown on Tt
322 map) and Spencer Formation (Ts)
EI Exploratory petroleum well—Showing name; upper number shows ele- Tsrk
eooteice RESERVE Bruer 1 __ vation (in meters) from which well depths were measured (commonly
TIN 4 109 from kelly bushing) and lower number shows elevation of bottom of Tsr
7582 well. Also shown are elevations of tops of formations in well relative
Tms 106 to -69 to sea level
Ts -69
Water well
e Reaches contoured horizon—Located to the quarter-quarter section
sunmenee:
q ny, © Gongraimtelinidete feenreuredshorisunstorsedtton ie tcueier DESCRIPTION OF MAP UNITS Tsm Scotts Mills Formation of Miller and Orr (1988) (Miocene and Oli-
i quarter section [The stratigraphic nomenclature and unit-age assignments on plates 2A, 2B, and 3 may not gocene)—Marine and nonmarine strata consisting of volcanic con-
: a Reaches contoured horizon—Accurately located conform to current usage by the U.S. Geological Survey] Sener! a eee see cues burrowed
H claystone, barnacle limestone, and inter! coal of nonmarine ori-
: a Constrains altitude of contoured horizon—Accurately located GEREN TRY 4 AD WOLOANTe RG REANERESTES ni eatisaerlt poorete sole eof the able For-
i. @ Locality of radiometric age determination(s)—Showing age(s) Maas bs os is a bs sari Ae ae ate on es
" 14.6 + 0.4 Southern Willamette Valley (part) and Coast Range Sie GER Boe espe lest end cc ode as Ona
Qns_ Nonmarine sedimentary deposits (Holocene and Pleistocene)— Tmo Molalla Formation of Lowry and Baldwin (1952) (Miocene and Oli-
OREGUNCXELORATTON Unconsolidated gravel, sand, and silt of fluvial and lacustrine origin; gocene(?))}—Pumiceous volcanic conglomerate and aquagene tuff
Wonigest includes the Linn Gravels and Willamette Silts of Allison (1953) and with tuffaceous paleosols (Miller and Orr, 1988). Contains early
: o “64 TEXACO Cooper Mountaing! Ure younger alluvium [yal] unit, older alluvium and related deposits [Qoal] Miocene fossil leaves (J.A. Wolfe, U.S. Geological Survey, written
46°00 “49° H 158 vs = 239 : unit, and terrace deposit and related alluvial material [Qt] unit of Piper commun., in Peck and others, 1964); radiometric dates from unit of
[oetaa TH 64 toct¥e Bee H (1942); radiocarbon dates from unit of 36,000 yr B.P. to present 15.9+1.0 Ma and 15.0+0.7 Ma determined by Fiebelkorn and others
T#l)49'to—82, 800. ues Tc 208 to-€4 —Sgiiche O Qls _ Landslide deposits (Holocene and Pleistocene) (1983)
‘ape te ee Ims-84 77 No 5 i ; ; Tms Marine sedimentary rocks (Oligocene and Eocene)—Tuffaceous silt-
Ts. 62474. basalts Qt High terrace gravels (Pleistocene)—Stratified gravel, sand, silt, and clay; stone and sandstone in the south becoming tuffaceous claystone and
~206 Ty =1063 : t cas ‘Tb deeply weathered; consists of the Lacomb and Leffler Gravels of Alli- mudstone to the north; equivalent in part to the Eugene, Keasey, and
ee ey ay umay ASacn ig oe PD Tis son (1953), terrace gravels of Baldwin (1964), Quaternary upper ter- Pittsburg Bluff Formations; also equivalent in part to Eocene and Oli-
A tee, Sats Gs a <N9 ‘4 race and Quaternary middle terrace of Beaulieu (1974), part of gocene sedimentary rocks of Bela (1981); tuffaceous marine sedimen-
Tr ales BEAVERTON faaer ve terrace deposit and related alluvial material [Qt] unit of Piper (1942), tary rocks of Baldwin and others (1955) and the Illahe Formation of
( a Qo A Oo TBEA) wee eee eo ul a Quaternary higher terrace deposits of Bela (1979, 1981), and high Thayer (1939); foraminiferal assemblages assigned to the Refugian
a as 7 terrace deposits of Brownfield (1982a, c); early to middle Pleistocene Stage in the south (McKeel, 1985) and the Refugian and late Narizian
in age (Allison, 1953) Stage in the north (Brownfield and Schlicker, 1981a)
H Tms Marine sedimentary rocks (Oligocene and Eocene)—Tuffaceous silt- Tbf — Basaltic flows (Oligocene and Eocene)—Basaltic flows that may be inva-
: stone and sandstone in the south becoming tuffaceous claystone and sive into the Fisher Formation (Tf) and questionable sills that may
7. mudstone to the north; equivalent in part to the Eugene, Keasy, and intrude the Fisher Formation (Walker and Duncan, 1989)
Hi Pittsburg Bluff Formations; also equivalent in part to Eocene and Oli- Tf Fisher Formation (Oligocene and Eocene)—Andesitic lapilli tuff and
H gocene sedimentary rocks of Bela (1981); tuffaceous marine sedimen- breccia, tuffaceous sandstone and siltstone, and pebble to boulder
y tary rocks of Baldwin and others (1955); and the Illahe Formation of conglomerate interbedded with flows of andesite, dacite, and basalt;
rf Thayer (1939); foraminiferal assemblages assigned to the Refugian interfingers to the northwest with marine strata of the Eugene Forma-
H Stage in the south (McKeel, 1985) and the Refugian and late Narizian tion; fossil leaves from unit indicate late Eocene to Oligocene age
: Stage in the north (Brownfield and Schlicker, 1981a) (R.W. Brown, in Hoover, 1963); radiometric ages from unit range
ry Tn Nestucca Formation (Eocene)—Tuffaceous shale and siltstone and from 40 to 35 Ma (Lux, 1982)
thin-bedded sandstone intercalated with pillow basalt, breccia, and tuff
(Baldwin and others, 1955); foraminiferal fauna from unit assigned to Cascade Range Foothills (part) and Northern Willamette Valley
late Narizian Stage (W.W. Rau, Washington Division of Geology and
Earth Resources, written commun. to Wells and others, 1983) Qns Nonmarine sedimentary deposits (Holocene and Pleistocene)—
Ts Spencer Formation of Tumer (1938) (Eocene)—Massive to thin-bedded Unconsolidated gravel, sand, and silt of fluvial and lacustrine origin;
tuffaceous mudstone and siltstone grading eastward to tuffaceous and includes the Linn Gravels and Willamette Silts of Allison (1953) and
volcanic rocks, and well-sorted shallow-marine micaceous, arkosic younger alluvium [Qyal] unit, older alluvium and related deposits
sandstone and siltstone with minor coal; correlative in part with the {Qoal] unit, and terrace deposit and related alluvial material [Qt] unit
Nestucca and Cowlitz Formations; foraminiferal fauna from unit of Piper (1942); radiocarbon dates from unit of 36,000 yr B.P. to
assigned to the Narizian Stage (McKeel, 1984, 1985). On cross sec- present
tions, divided into three units Qls _ Landslide deposits (Holocene and Pleistocene)
Tsu: Upper member—Tuffaceous mudstone, siltstone, and minor sandstone Qt High terrace gravels (Pleistocene)—Stratified gravel, sand, silt, and clay;
Tsl Lower member—Micaceous, arkosic sandstone, siltstone, and minor deeply weathered; consists of the Lacomb and Leffler Gravels of Alli-
acl son (1953), terrace gravels of Baldwin (1964), Quaternary upper ter-
Tsv Volcanic rocks—Basalt, andesite, and tuff; grade into upper member to race and Quaternary middle terrace of Beaulieu (1974), part of
NAHAMA AND WEAGANT Bieat terrace deposit and related alluvial material [Qt] unit of Piper (1942),
ah Ty Yamhill Formation (Eocene)—Massive to thin-bedded marine siltstone Quaternary higher terrace deposits of Bela (1979, 1981), and high
with thin: iniatbede of aykosie cleuconitic, and basaltic’ eindstona: terrace deposits of Brownfield (1982a, c); early to middle Pleistocene
i FE. Te ie 149 interfingers with the Tillamook Volcanics to the northwest and in age (Allison, 1953)
od ahha 48a arc-related(?) volcanic rocks to the southeast. On cross sections, QTb Basalt and basaltic andesite (Pleistocene and Pliocene)—Olivine basalt
Ts? -965 divided into four units and basaltic andesite and some pyroclastic materials of local extent,
\1y?/2996 to 1508: Tyum Upper mudstone member—Siltstone, mudstone, and minor sandstone; vents at Highland Butte; equivalent to the Boring Lavas of Allen
SCALE 1: 100 000 foraminifers from unit indicate deposition at upper to middle bathyal (1975); radiometric dates from unit range from 5 Ma (Luedke and
5 A ; é . ‘i : - 2 4 aries depths (McKeel, 1984, 1985) Smith, 1982) to 612423 ka (R.A. Duncan, Oregon State University,
cece Tym Miller sand of Bruer and others (1984)—Informally named unit. Tuf- written commun. to I.P. Madin, Oregon Department of Geology and
; i , A s ; . auieS faceous to atkosic sandstone and interbedded siltstone becoming Mineral Industries, 1990) radiometric date from unit from the Oregon
== more volcanic rich and conglomeratic to the southeast; foraminifers City plateau of 2.6 Ma (R.A. Duncan, Oregon State University, and
CONTOUR INTERVAL 60 METERS from unit indicate deposition at upper bathyal to inner neritic and N.S. MacLeod, U.S. Geological Survey, written commun. to R.D.
MOAIGE CONTA OEGES nonmarine depths (McKeel, 1984, 1985). Largely restricted to the Swanson, 1985); also includes basalt, basaltic andesite flows, and
NATIONAL GEODETIC VERTICAL DATUM OF 1929 southern Willamette Valley basaltic breccia of Snow Peak volcano; radiometric dates from unit of
1996 MAGNETIC DECLINATION AT SOUTH EDGE OF SHEET IS 19° EAST Tylm Lower mudstone member—Tuffaceous mudstone and siltstone with 2.80.3 Ma and 3.3+0.6 Ma (Verplanck, 1985)
minor interbedded sandstone; foraminifers from unit indicate deposi- Tf Fluvial and lacustrine(?) sedimentary deposits (Pliocene and
tion at middle bathyal to outer neritic depths (McKeel, 1985) Miocene)—Clay, silt, sand, and gravel. Largely fluvial (A.R. Niem,
Tyy __ Voleanic rocks—Tuff, basalt, dacite, and andesite; grade into the Miller Oregon State University, and C.D. Peterson, Portland State Univer-
eanationbetest sity, personal commun. to I.P. Madin, Oregon Department of Geol-
ET Tyee ll Fore tenia Encene ee nettle intarsescied pemediciieeto ogy and Mineral Industries, 1989) but may contain some lacustrine
fine-grained, micaceous, feldspathic, lithic or arkosic marine sand- sedimentary deposits. Equivalent to the Sandy River(?) Mudstone and
stone and micaceous, carbonaceous siltstone of turbidite origin; finer Troutdale Formation in the Portland area; includes unnamed fluvial
grained distal facies to the north; foraminiferal fauna from unit eee deposits on the cross sections in the southern Willamette
referred to Ulatisian Stage (Molenaar, 1985) oy.
Tsr — Siletz River Volcanics (Eocene)—Submarine pillow lavas, massive flows, Sardine Formation (Pliocene and Miocene)
tuff breccias and flow breccias of tholeiitic and alkalic basalt and asso- Tsau Volcanic rocks, undivided (Miocene)
Base from U.S. Geological Survey 1:100,000 ciated sills and dikes, and calcareous sandy tuff; abundant zeolites and i ; f . A
Oregon City, 1982; yea River’ 1980 calcite veining; upper part of unit pace intercalated tuffaceous ee reat (Wilson ateilealie Tose serelhis LRN I 9
Nehalem River, 1979; and Vancouver, 1979 5 shale, siltstone, basaltic sandstone, and locally derived basaltic con- includes basaltic andesite at Washburn and Lone Pine Buttes; potas-
Projection: Universal Transverse Mercator glomerate; foraminiferal fauna from unit are referred to the Ulatisian sium-argon age from unit of 1,920.3 Ma (Verplanck, 1985)_
25,000-foot grid ticks based on Oregon coordinate system, Geology By Robert S. Yeats, Kenneth S. Werner, and and Penutian Stages of Mallory (1959) (see also Snavely and others. Tsat Tuffaceous' nonmarine sedimentary rocks (Mlocene)—Fine- to
north zone. 1927 North American Datum Thomas A. Popowski 1968; McWillams, 1980); radiometric ages from unit range ae coarse-grained tuffaceous siltstone and sandstone, pebble conglomer-
R3E 0 50.743.1 to 8 141.5 Ma (Duncan, 1982) ate, agglomerate, volcanic cobble conglomerate, basaltic andesite
123230 R6W. RSW QTb oe = Tsrk Kings Valley Siltstone Member—Thin-bedded, dulierereirsy flows, and minor interbeds of air-fall tuff (Hampton, 1972; Walker
op deep-marine siltstone and shale; contains thin lenses of basaltic sand- Se aca 1B ses een camer ute Gy never (1982)
QTb Y i Tsav Volcanic rocks (Miocene)—Mudflow breccia, water-laid tuff, and tuff
Reed AUROR Ms Tock mH XS ae gone; ocers Pealy (Hampton, 1972). Equivalent to the Rhododendron Formation of
B 3 Hodge (1933)
~700. ISSUR FACE Sais Cascade Range Foothills (part) and Southern Willamette Valley (part) Te Columbia River Basalt Group (Miocene), undivided—Subaerial tholei-
- = We : ; : itic basalt flows; in places, separated by baked tuffaceous sedimentary
5 an Qns Nonmarine sedimentary deposits (Holocene and Pleistocene)— rocks; locally deeply weathered to lateritic soil. In the mapped area,
{ Yo Unconsolidated gravel, sand, and silt of fluvial and lacustrine origin; group is represented by the Yakima Basalt Subgroup, which is divided
TAS includes the Linn Gravels and Willamette Silts of Allison (1953) and into the Wanapum Basalt and the Grande Ronde Basalt
T4s = younger alluvium [Qyal] unit, older alluvium and related deposits [Qoal] Wanapum Basalt
/ ) fa Be ere se ens aa aa a niet Biber Tewt Frenchman Springs Member—Thin flows of gray to dark-gray,
1h ar Ss Y Agi Be iocar oH lates ro ual e 000 yr B.P. to present medium-grained, commonly plagioclase-phyric basalt; age is 15.3 Ma
© INS Pras “A Ols indslide deposits (Holocene and Pleistocene) Tegr Grande Ronde Basalt —Flows of dark-gray to black, glassy to mostly
5h “DAMON Stauffer Fatms 35-1 : ON Qt High terrace gravels (Pleistocene)—Stratified gravel, sand, silt, and clay; Sra Hels ete pc Sa HEE Ee MRC 18 ees EY i
y 4 62) |} ; . deeply weathered; consists of the Lacomb and Leffler Gravels of Alli- nee vale
/ 387 iS ia, 1ons SS son (1953), terrace gravels of Baldwin (1964), Quaternary upper ter- TS i ce Sn One CHM ane poms 0d met)
j 2) Aiea ans [ \\Imo Z Faceldndl Onde vnaty muddle toreare'ak Baauliali 1974 -partor teusse (Miocene)—Poorly indurated, friable, fluvial basaltic conglomerate,
a le come BW, Tegr 343 Ais TA Tb deposit and related alluvial material [Ot] unit of Piper (1942), Quater- EWA IG URS Een) We Se ciealiee NUS AU AS
iy “600 Mena, Tr 23 tol-787, Ss mary eileen ate cemcaitstot ela (1579 )1H i) andinich terrace low-marine to estuarine mud rocks and tuffaceous siltstone and sand-
—- Tht ma Til . deposits of Brpwnfield (19825, ¢); early to middle Pleistocene in age stone. Fluvial deposits in the upper part of the formation are derived
| = ee A eey (Allison, 1953) from, intercalated with, and invaded by flows of the Grande Ronde
WILLAMETTE VALLEY —s NS re 2 QTb Basalt and basaltic andesite (Pleistocene and Pliocene)—Olivine basalt easel Ute Sealineseso imei iGalant ley eiaalioilne Wg ea ial Plier
fpegcere and basaltic andesite, and some pyroclastic materials of local extent, Littl mee Bit Ferment: Pear wate uncertain ti
Ve > 334 vents at Highland Butte; equivalent to the Boring Lavas of Allen Tile, VENUS Lette Wiiarulte aii e (iltnedce cited @iisee ng eau!
ic wee (1975); radiometric dates from unit range from 5 Ma (Luedke and blage of basalts and basaltic andesites complexly interstratified with
THI? 52 to -265 Smith, 1982) to 612+23 ka (R.A. Duncan, Oregon State University, volcaniclastic deposits of basaltic to rhyodacitic composition; includes
Feicrioip wera GiHHSH CRRA fol UD! MEH OFSHOR DuspSrimento? Géoloayand thyodacitic to andesitic ash-flow and airfall tuffs, lapili tuff and tuff
58 Mineral Industries, 1990), radiometric date from unit from the Ore- LCS NCI MISiiete SO TSS Recs Bh pall Ogee Nay
ees. OREGON NATURAL GAS gon City plateau of 2.6 Ma (R.A. Duncan, Oregon State University, to coarse-grained nonmarine tuffaceous sedimentary rocks, and volca-
TH 45 to -294 DeShazer 13-22 and N.S. MacLeod, U.S. Geological Survey, written commun. to R.D. nic conglomerates; potassium-argon ages from unit range from 35 to
Togr +294 = Swanson, 1985); also includes basalt, basaltic andesite flows, and He ein ibe reyp Pk) Clip Ceaeca ete A Saute se) EM Ehe
aa ee i sn ieay basaltic breccia of Snow Peak volcano; radiometric dates from unit of aati me | ; ae
TLE edposs le A Uae pas 2.80.3 Ma and 3.3+0.6 Ma (Verplanck, 1985) Tiba Porphyritic andesite (Miocene)—Massive porphyritic andesite
i Tms =481 ; Tfl Fluvial and lacustrine(?) sedimentary deposits (Pliocene and Tibb Basalt and basaltic andesite (Miocene}—Basalt and basaltic andesite
f Ts | -616 & Miocene}—Clay, silt, sand, and gravel. Largely fluvial (A.R. Niem, flows and flow breccias
Ii ONES © BH EXPLORATION Rote Oregon State University, and C.D. Peterson, Portland State Univer- Tsm Scotts Mills Formation of Miller and Orr (1988) (Miocene and Oli-
7] - sity, written commun. to LP. Madin, Oregon Department of Geology gocene)—Marine and nonmarine strata consisting of volcanic con-
ane 400 F008 and Mineral Industries, 1989) but may contain some lacustrine sedi- glomerate, arkose, and mudstone, tuffaceous sandstone, burrowed
SON RAT RHAL Ras 2 Th 41402156 mentary deposits. Equivalent to the Sandy River(?) Mudstone and claystone, barnacle limestone, and interbedded coal of nonmarine ori-
59 Tegr -156 Troutdale Formation in the Portland area; includes unnamed fluvial gin; interfingers with nonmarine sedimentary rocks of the Molalla For-
aa > Tlb, -313 to-1006?7 sedimentary deposits on the cross sections in the southern Willamette mation. Dated as late Oligocene and early Miocene based on
Til. 140-2293 1 EO: Valley mollusks, barnacles, vertebrate fossils, and echinoderms (Orr and
Tegr =293 REICHOLD Bagdanoff 23-28 RH EXPLORATION Sardine Formation (Pliocene and Miocene) Miller, 1986)
Tms —440 =. 59 An 1 Tsab Basalt (Pliocene and Miocene)—Basalt at Marks Ridge; radiometric Tmo Molalla Formation of Lowry and Baldwin (1952) (Miocene and Oli-
% ear Ph = -1771 AS date from unit of 4.5+0.28 Ma (Verplanck, 1985) gocene(?)}—Pumiceous volcanic conglomerate and aquagene tuff
eo = ag -267 oan toe: Tsau Volcanic rocks, undivided (Miocene) with tuffaceous paleosols (Miller and Orr, 1988). Contains early
= Teas Te. ae ‘Aton PARE ORT re Siena reke a Je Miocene fossil leaves (J.A. Wolfe, U.S. Geological Survey, written
Ts’ -6097 * Tent CaP © Tsaa pei ( liocene)— Pe Le We On rte QAline :e OT aOn ASG: commun., in Peck and others, 1964); radiometric dates from unit of
© Ty 84010-1771 The 192 to £9627 includes basaltic andesite at Washburn and Lone Pine Buttes; potas- 15.9+ 1.0 Ma and 15.0+0.7 Ma determined by Ficbelkorn and others
Hep f= e sium-argon age from unit of 1.90.3 Ma (Verplanck, 1985) (1983)
REICHOLD Fin Tsat Tuffaceous nonmarine sedimentary rocks (Miocene)—Fine- to Trig diMarine taedimentary rocker Olsacene andi Eocens)=<1ctarecterait
oe | coarse-grained tuffaceous siltstone and sandstone, pebble conglomer- stone and sandstone in the south becoming tuffaceous claystone and
2146 ate, agglomerate, volcanic cobble conglomerate, basaltic andesite ranidatone tote noriuectialatinipart toro buceneuonceusand
Tms 52 to -92? flows, and minor interbeds of air-fall tuff (Hampton, 1972; Walker and : ae aes ae ites
Tener : : Pittsburg Bluff Formations; also equivalent in part to Eocene and Oli-
Ty Liga Duncan, 1989); includes the Fern Ridge Tuffs of Thayer (1939) gocene sedimentary rocks of Bela (1981); tuffaceous marine sedimen-
Tsr 1019 to~2146 Te Columbia River Basalt Group (Miocene), VES aCe ere tholelitic tary rocks of Baldwin and others (1955), and the Ilahe Formation of
basalt flows; in places separated by baked tuffaceous sedimentary Thayer (1939); foraminiferal assemblages assigned to the Refugian
rocks. In the mapped area, group is represented by the Yakima Basalt Stage in the south (McKeel, 1985) and the Refugian and late Narizian
RESERVE Bruer1—_ Subgroup, which is divided into the Wanapum Basalt and the Grande Stage in the north (Brownfield and Schlicker, 1981a)
109 Heteiee! Tbs Submarine basalt (Eocene)—Pillow basalt and submarine basalt breccia
31582 Wanapum Basalt and lapilli breccia and intrusive rocks (Wells and others, 1983); possi-
Tms 106 to.-69 Tewf Frenchman Springs Member—Thin flows of gray to dark-gray, bly equivalent to either the Tillamook Volcanics or the Siletz River
Ts 3, medium-grained, commonly plagioclase-phyric basalt; age is 15.3 Ma Wale nies
Si renee Teor Grande Ronde Basalt—Flows of dark-gray to black, glassy to mostly Twh Basalt of Waverly Heights and associated sedimentary rocks, undi-
: aphyric, locally vesicular tholeiitic basalt; age is 16-15.6 Ma in Wil- idea | (cere ye ibe alk bacalivat vis aarneine ieedimmeniaryitecles
___ lamette Valley aa ‘ ‘ (Beeson, Tolan, and Madin, 1989). Two flows from unit have potas-
Gos. Tib Little Butte Volcanics, undivided (Miocene and Oligocene}— sium-argon ages of about 40 Ma (R.A. Duncan in Beeson, Tolan, and
Assemblage of basalts and basaltic andesites complexly interstratified Madin, 1989)
with volcaniclastic deposits of basaltic to rhyodacitic composition; :
includes rhyodacitic to andesitic ash-flow and air-fall tuffs, lapilli tuff
mal A l and tuff breccia, andesitic to dacitic mudflow deposits, massive to bed- INTRUSIVE ROCKS
123°30° R3W 123°00' ded, fine- to coarse-grained nonmarine tuffaceous sedimentary rocks,
a i All Areas
and volcanic conglomerates; potassium-argon ages from unit range
from 35 to 22 Ma in the map area, with suspect ages older than 35 Ti __ Intrusive rocks, undivided (Tertiary)—Sills and dikes of granophyric gab-
Ma (Lux, 1982) bro and granophyric diorite in the Coast Range south of Sheridan,
GEOLOGIC MAP OF THE NORTHERN WILLAMETTE VALLEY, CLACKAMAS, MARION, MULTNOMAH, POLK, TILLAMOOK, WASHINGTON, AND YAMHILL COUNTIES, OREGON rns act ad rgdcte Moan) Das fo oie vk cm cote cnr ba an dr nh Co are
9 > i) plexes north of Sheridan; basalt, basaltic andesite, and andesite with minor
Tibb Basalt and basaltic andesite—Basalt and basaltic andesite flows and dacite to rhyodacite in the western Cascade Range; ages range from
By flow breccias Eocene to Miocene in the Coast Range (Wells and others, 1983) and
Tibw Welded to nonwelded ash-flow tuff—Mostly vitric-crystal and vitric from Oligocene to Pliocene in the western Cascade Range (Walker

1Department of Geosciences, Oregon State University, Corvallis, OR 97331
2Unocal Corp., Lafayette, LA 70505

U.S. Government Printing Office: 1996--774-067

Robert S. Yeats,! Kenneth S. Werner,!? and Thomas A. Popowski!
1996

ash-flow tuff (Walker and Duncan, 1989)

and Duncan, 1989). Queried where uncertain

o

Se eles