DEPARTMENT OF THE INTERIOR
UNITED STATES GEOLOGICAL SURVEY

121°00° ri p
47°30" RISE 1900 660000

52500000 B
T23N

150 000 FEET
(NORTH)

750
T22N

700

15°
a
z
@
xg
3
s
8
al

650 000 FEET,
(SOUTH)

47°00" jy Pee NS

Stren RISE 7 900 000 FEET (SOUTH) 65 Rie

Base from U.S. Geological Survey, 1975

Projection and 10 000-meter grid, zone 10:
Universal Transverse Mercator. 1927 North
American Datum

50 000-foot grid ticks based on Washington
coordinate system, south and north zones

A
FROST < *
METERS MOUNTAIN 3 2
S S SOUTH CLE
= Thf Tta Ti T B Tgn2. = ELUM RIDGE
Tte _Tte 8 Te §
1500 re © ps PIMP ais § Tgn2
1000 ee LLLASKZ EE
son f 5 CZ, Lp
‘Tdg
SEA LEVEL \

R 16 E :2 000 000 FEET (NORTH)

45"

TRUE NORTH

(3
Ss
‘2
iS
iG
ie
=

APPROXIMATE MEAN
DECLINATION, 1982

Yakima River

45° 07

RITE

1.950

LOOKOUT
MOUNTAIN
Qisb Qksm Qls

92 Trl Tm

SWAUK PRAIRIE
Qibs Okst

(CHELAN) 30°

Cascade i

30° (YAKIMA 1.250 000) R19

SCALE 1:100 000

O___} 284 gO KILOMETERS
1 ° 1 2 3 4 __5 MILES
5000 oO 5000 10 000 15 000 20 000 25 000 FEET

CONTOUR INTERVAL 50 METERS
NATIONAL GEODETIC VERTICAL DATUM OF 1929

WENATCHEE MOUNTAINS
“x

3
Teanaway dikes Qls 33 Tsp
Ts ayy .

Tsp

Tsc

Tronsen Creek

LEAVENWORTH
FAULT ZONE

Mission Creek

15° 2150 ui) R21E

15!

ee

a a

a

QUADRANGLE LOCATION

CHIWAUKUM GRABEN

Bear Creek

Te

2 100 000 FEEFISOUTH)

Thickness of unconsolidated units is exaggerated

VERTICAL EXAGGERATION X1.25

INTERIOR—GEOLOGICAL SURVEY, RESTON, VA —1987—Ge0603

12_R22E 2 200

100
‘SEA LEVEL
100
200

120°00°
47° 30°

‘gd

T23N

528

T21N
ne
- sag
a8 700
eS 15"
>
&
8
ert
8
=
T20N

pty or

TIBN

52100000N

47°00"
120° 00'

Geology mapped by R. W. Tabor, R. 8. Waitt. Jr.,
and V. A. Frizzell, Jr., 1975-79; D. A. Swanson,
G. R. Byerly, and R, D. Bentley, 1976-77; Sharon
Allshouse and Eduardo Rodriquez, 1975; Jay
Coburn and Ron Tal, 1976; Bill Gaum and

Kim Marcus, 1977; D. B. Booth and Elizabeth
Lincoln, 1978; Joe Marquez, 1979

MISCELLANEOUS INVESTIGATIONS SERIES

MAP I-1311
CORRELATION OF MAP UNITS
‘pe, i align SURFICIAL DEPOSITS
years before Wenatchee and Columbia drainage basins
present Mass
(Estimates in All drainage Yakima and Peshastin Landslide wastage
parentheses) basins drainage basins Flood deposits deposits Alluvial deposits deposits Glacial deposits _Eolian deposits
oF f ; t——11 : t—i : Vf , 1
ay | ap ae | ow fe at | {_asy | arg |{ Ge ‘1k 1
(0.01) - ce jz
Qwt! 7
Qifo | air
cay aT za
Qisy
>
Qis 3
Qsi Lz
: A
2
Qibt
-Qlso.
(0.018) —
Qkit | Qkim | Qkis | kil
Qkt | Oks
(0.14)- ‘Okst Okss i Qfg
(0.75) - Qim
Unconformity
BEDROCK
| :
Shee
2
L
8
14-165 - =
2
5
8
r=
>
=
a
z
Ceara B
Tda
30 - h ~
aaa
Southwestern Eastern sequence Small Tertiary 2
sequence Western sequence (Chiwaukum graben) intrusive bodies L H
L F 1 1
VE Vf i 1 z
- fo)
= Tw? Tw
Uneonformity x
[x — Tete Ton
|—e—Teteb
Fabectoee Fe)
Te al
Trhf Ny
47- > ee? 2
Mill ee a :
il ro
f Tesh |
52-
Unconformity _ 4
Pre-Tertiary basement
93 - } 38 3 7 £8
+ BO
ob 88
228
| 2883 o 48
150- ‘+ rneaag L&Snee
236283 | 5S9eho
g 3 1 R86
558888 = 2°88
‘J 252
amg

Areal percentage underlain by dikes of
Teanaway dike swarm

0-80 1-10

Contact—Solid where established in
reconnaissance mapping by authors; long
dashed where derived from other workers
(see fig. 2); short dashed where inferred;
dotted where concealed or indicating
contact of coherent unit in landslide (unit
symbol in parentheses)

—_t— High-angle fault—Dashed where inferred;
dotted where concealed. Bar and ball on
downthrown side

~+— + Thrust fault—Dashed where inferred; dotted
where concealed. Sawteeth on upper plate

Major folds—Dotted where concealed.
Arrows along axis show direction of plunge

<f— \ Antictine
>—— _ Syndine

Monoclinal hinges—Arrows on steep limb

pointing down dip
en Bend up
+t Bend down
—f— Regional arch

Strike and dip of bedding—Ball on strike line
indicates top is toward number

a Inclined
ard Overturned
a Vertical—Ball indicates top on vertical bed
turned toward 90°
we Variable
® Horizontal
Strike and dip of foliation in igneous and
metamorphic rocks
Fe Indined
we Variable
Seiad Vertical
Bearing and plunge of mineral lineation—
Usually combined with foliation
—° inclined
bod Horizontal

ee Direction of basalt flow

——— Zone of sheared rock—Not shown in
serpentinite within dike swarm zone (Kmsd)

--——-—— Crest of moraine

Landslide—Arrow shows direction of
movement. Unit in parentheses indicates
coherent block

e& Dated sample locality—See table 1

Note: Sheets 1 and 2 of the geologic map of the Wenatchee Quadrangle
are from a scanned image of I-1311. Some of the map's explanitory
material has been rearranged to fit this digital format.

GEOLOGIC MAP OF THE WENATCHEE 1:100,000 QUADRANGLE, CENTRAL WASHINGTON

By

R. W. Tabor, R. B. Waitt, Jr., V. A. Frizzell, Jr., D. A. Swanson,
G. R. Byerly, and R. D. Bentley

1982


Qis

Qy

Qp

Qidm

Qibt

Okit

Ttm

DESCRIPTION OF MAP UNITS
SURFICIAL DEPOSITS
All drainage basins

LANDSLIDE DEPOSITS, UNDIFFERENTIATED—Poorly sorted deposits ranging from
muddy boulder gravel to bouldery mud; clasts are angular and of only one or two local rock
types; most slides have hummocky surfaces, bulbous toes, and moats at the head and
margins; smaller slides generally head at theater-shaped scars; some large slides merge
headward with block slides (Qlsb). Small slides designated by arrows only, showing
direction of movement

LANDSLIDE OF LARGE BLOCKS—Mainly large intact blocks whose original internal
stratigraphy is partly to wholly preserved (where mapped, internal stratigraphy designated
in parentheses); slides occur mainly as the headward parts of large landslides derived from
regional escarpment of the Yakima Basalt Subgroup; large incipient slide near Mission
Peak includes nonrotated blocks, of which the largest, essentially in place, measures 2000
x 1000 x 150 m. Elsewhere blockslides are of older rock units

MANMADE FILL AND MODIFIED LAND

SIDESTREAM ALLUVIUM—Moderately sorted boulder-to-pebble gravel of the few rock
types that crop out in relatively small drainage basins

ALLUVIUM OF FANS—Poorly sorted boulder gravel to gravelly sand; subangular gravel
clasts are generally of one or two rock types; forms fans of distinctly steeper gradient than
floor of sidestream or trunk-stream valleys but in many places merging gradationally with
deposits mapped as Qs, Qy, Qp, Qc, and Qw

Yakima and Peshastin drainage basins
ALLUVIUM OF YAKIMA RIVER—Boulder to pebble gravel containing rounded stones:
largely of volcanic and dike rocks, moderately of metamorphic and sedimentary rocks, and
sparsely of intrusive rocks. No weathering or soil
ALLUVIUM OF PESHASTIN CREEK—Subrounded cobble to boulder gravel of many rock
types but dominantly amphibolite (KJia) and quartz diorite (Kmsq). No soil
LAKEDALE DRIFT—Divided into:

Hyak subdrift, till—Diamicton of angular to subrounded clasts in muddy sand matrix
forming moraines and drift blanket near heads of valleys; clasts consist of several rock
types; A-C soil about 0.75 m thick

Domerie subdrift, mainstream outwash—Gravel lithologically like Qy but forming terrace
about 5 m above Yakima River near Cle Elum that grades upstream to moraines 9 to 30
km beyond western map boundary. A-C soil about 1 m thick

Ronald subdrift, mainstream outwash—Cobble gravel lithologically similar to Qy but
forming terrace near western map boundary lower than Bullfrog outwash surface
(Qibm) and roughly 12m above modern Yakima flood plain. Grades upvalley to
moraine 5 km beyond western boundary of map

Bullfrog subdrift—Divided into:

Till—Poorly sorted muddy boulder diamicton forming moraine atop Lakedale terrace in
Yakima River valley at western boundary of map; in Peshastin Creek valley, forms
flat-topped mass at mouth of Ingalls Creek and crested moraines immediately
downvalley; lithology of clasts similar to Qy or Qp; weak A-C soil. In upper Naneum
Canyon, consists of angular clasts of Grande Ronde Basalt, a few of them vaguely
striated; forms paired nested moraines in headwaters of Naneum Creek

Mainstream alluvium—Mixed-lithology cobble gravel forming distinct terrace 50 m
above Yakima River at upstream (western) map boundary, grading downvalley to 18
m above the river at southern map boundary; material identical to Qy but includes
discontinuous mantle of loess as thick as 0.5 mand supports soil no thicker than 130
cm, no redder than 7.5 YR, and lacking an argillic B-horizon; grades from moraines
(Qlbt) at western boundary of map. In Peshastin drainage, forms moraine
lithologically like Qp and graded to Qlbt

Sidestream alluvium—Lithologically and texturally similar to Qs but supports a weak
soil; forms terraces 10 to 20 m above Holocene surfaces in Kittitas Valley along
Yakima River and 4 to 7 m above floor of Dry Creek valley

Undifferentiated gravel—Lakedale terrace near Ellensburg containing both mainstream
and sidestream gravel
KITTITAS DRIFT—Divided into Indian John and Swauk Prairie subdrifts:
Indian John subdrift—Divided into:

Till—Boulder diamicton lithologically similar to Qlbt forming ill-defined moraine at
Indian John Hill on southem side of Yakima Valley and distinct left-lateral moraine on
the southern slope of Cle Elum Ridge

Mainstream outwash—Boulder-to-cobble gravel forming prominent 85-m-high terrace
heading at Indian John moraine; occurs discontinuously in Yakima canyon south of
Lookout Mountain and as nearly continuous terrace 50 to 25 m above the modern
flood plain along southern side of Kittitas Valley; lithologically similar to Qy but
contains distinctly weathered stones and locally is mantled with loess as thick as 1.5 m;
soil contains a textural B-horizon as thick as 2.5 m and as red as 5 YR

Sidestream alluvium—tn Kittitas Valley basaltic gravel similar to Qs, forming distinct
terrace on northern side of Yakima River paired to mainstream outwash (Qkim) south
of river. Continuously traceable up Dry Creek and Green Canyon Creek valleys;
terrace is best topographic reference for correlation of sidestream terraces in northern
Kittitas Valley; apparently correlative terraces in upper Teanaway River valley are 10
to 12 m above modern flood plain

Lacustrine deposits—Along irrigation ditch in lower Teanaway valley, thin-bedded silt
and clay containing faceted ice-rafted stones as large as 20 cm; in Yakima River valley
near Teanaway River confluence, an almost horizontal terrace of sand and gravel at
altitude 640 m; graded to conspicuous outwash terrace (Qkim) immediately
downstream. As mapped, includes sidestream alluvial and deltaic debris similar to
Qkis

Swauk Prairie subdrift—Divided into:

Younger lapustrine deposit—Poorly exposed deposit 85 m above Teanaway River on
eastern end of Cle Elum Ridge of thin-bedded sand, silt, and clay containing
dropstones as large as 4 cm

Till—Boulder diamicton of same diverse rock types as Qy; forms massive morainal
embankments at Thorp and Swauk Prairies and distinct nested moraines in saddle on
Lookout Mountain; at Swauk Prairie is capped by as much as 3 m of loess that includes
a buried paleosol having a 2.8-m-thick textural B-horizon as red as 5 YR; at Thorp
Prairie is only thinly and discontinuously capped by loess. Roadcuts briefly exposed in
1977 on eastern slope of Swauk Prairie revealed two layers of till separated by
nonglacial sand and mud

Mainstream outwash—Gravel similar to Qy forming distinct terrace along southern side

of Yakima River; terrace grades downvalley from 100 m above river at Thorp Prairie
moraine to 40 m above river at southern boundary of map

Sidestream alluvium—In northern Kittitas Valley, basaltic gravel forming terraces
intermediate in height between Indian John (Qkis) and Thorp (Tts) sidestream terraces;
sand, gravelly sand, and sandy gravel form broad terraces about 35 m above floor of
each fork of the Teanaway River

Older lacustrine facies—2-m bed of thin-bedded, light-gray to grayish-blue clay and
interbedded silt; clay contains rare dropstones of coarse sand and granules; overlies
older till; underlies 3-m bed grading upward from very fine sand to coarse sand that in
turn underlies till (Qkst) forming Swauk Prairie. Causes landsliding in new roadcuts on
outer slope of the Swauk Prairie moraine

KITTITAS DRIFT, UNDIFFERENTIATED—Divided into:

Till—Till forming lateral moraines in upper Naneum Canyon outside Qibt moraines;
composed of unsorted angular to subrounded clasts of Grande Ronde Basalt
inconspicuously striated and faceted; surface soil in places shows an argillic B-horizon.
Similar deposits lithologically like Qp form moraines on both sides of Peshastin Creek
valley and in lower Hansel Creek
Sidestream gravel—in Kittitas Valley, terrace gravel of clasts of Grande Ronde Basalt;

forms terrace above Lakedale and Holocene sidestream surfaces but below level of
Thorp sidestream surfaces. In Peshastin valley similar terrace deposits lithologically
reflect the local crystalline bedrock

LOOKOUT MOUNTAIN RANCH DRIFT—Diamicton containing rounded to subangular,

faceted, striated stones of diverse rock types similar to Qy; forms subdued moraines 0 to 85

m above the outer Kittitas moraine (Qkst) on Lookout Mountain; soil contains 7 YR to 5

YR argillic B-horizon at least 45 cm thick; correlative moraine along western side of Horse

Canyon

THORP GRAVEL—Divided into:

Mainstream alluvium—Weakly cemented moderately sorted cobble to pebble gravel with
thin interbeds of sand, silt, and tephra; gravel clasts subangular to rounded; diverse rock
types dominated by durable silicic volcanic rocks evidently derived from the underlying
Ellensburg Formation; forms conspicuous terrace along both sides of Yakima River in
Kittitas Valley 220 to 70 m above the river, distinctly above the Qksm terrace. Soil
locally has reddish argillic B-horizon as thick as 50 cm

GEOLOGIC MAP OF THE WENATCHEE 1:100,000 QUADRANGLE, CENTRAL WASHINGTON

By

R. W. Tabor, R. B. Waitt, Jr., V. A. Frizzell, Jr., D. A. Swanson,

Sidestream alluvium—Weakly cemented, moderately sorted boulder to cobble gravel of
angular to subrounded clasts of Grande Ronde Basalt; forms high terrace that slopes
from northern mountain front of Kittitas Valley to the mainstream terrace (Ttm);
contains minor chert, opal, vein quartz, quartzite,and durable felsites, none of which
occur within modern drainage basins incised in the Thorp; surface clasts have thick rinds
and deep cracks

Wenatchee and Columbia drainage basins

Qc | ALLUVIUM OF COLUMBIA RIVER—Gravel containing rounded clasts as large as 30 cm;
widely diverse rock types, including many medium-grained granitic to gneissic rock types
with color indices (CI) below 20 but only a few more mafic varieties; indudes stones of
Swakane Biotite Gneiss, Yakima Basalt Subgroup, many varieties of porphyritic dike
rocks, quartzite, and chert-pebble conglomerate; below Rock Island greatly enhanced in
clasts of basalt

Qw | ALLUVIUM OF WENATCHEE RIVER—Cobble-to-boulder gravel containing rounded
clasts of coarse medium-grained quartz diorite, grandiorite, and weakly foliated gneiss with
ClI>20, derived from quartz diorite of Mount Stuart batholith but contains only a few
granitic rocks with CI<20; includes muscovite and biotite gneiss, dark-colored
fine-grained schist, green amphibolite, hornfels, several other metamorphic rock types,
and various dike rocks. In map area contains small but conspicuous component of
pyroxene- and amphibolite-bearing porphyry derived from Eagle Rock (north of map
boundary) and small component of the Yakima Basalt Subgroup derived from landslide
and debris-flow deposits upvalley (north) of map boundary

BOG DEPOSITS—Mud and peat

risk
ie

Qt TALUS DEPOSITS—Loose angular locally derived boulders forming steep slopes
HOLOCENE DRIFT—Divided into:

Younger subdrift—Inner cluster of Neoglacial moraines (informally Brynhild) of angular to.
subangular quartz-diorite boulders in upper basin of Enchantment Lakes area (2);
average lichen cover less than 5 percent; Rhizocaron thallus to 12 mm; maximum depth
of weathering pits 6 cm; depth of soil oxidation 2 cm; devoid of trees and overlying
tephra. Only moraine crests shown on map

/yOs0 Older subdrift—Outer moraine (informally Brisingamen) of quartz-diorite boulders in
Enchantment Lakes area beyond limits of Brynhild moraines; average lichen cover 20 to
80 percent; maximum diameter of thallus of Rhizocaron 210 mm; weathering pits as
deep as 13 cm; depth of soil oxidation 23 cm or more; in places supports stands of
western larch; overlain by Mazama tephra. Only moraine crests shown on map

Qrg | ROCK-GLACIER DEPOSITS—Angular locally derived boulders forming bulbous tongue

Z Qe | EOLIAN DEPOSITS—Loose well-sorted medium sand deflated from Quaternary deposits
7 along the Columbia River

LOESS—Deposits of wind-deposited silt

GRAVEL OF LATE FLOODS—Divided into:

Qify Younger-phase deposits—Surfaces of gravel generally less than 30 m above river, at West
Bar and Malaga separated from Qlfo by steep erosional scarp that truncates giant
current dunes of Qifo; some bars form broad whaleback having shallow moat at inner
margin; surfaces generally not ornamented with giant current dunes but densely studded
with boulders to 3 m in intermediate diameter, rarely as large as 10 m; riverward slopes
of several bars of Qcg! and Qifo as high as 90 m above the river similarly
boulder-studded. Not everywhere distinguishable from unit Qifo

Qifo Older-phase deposits—Surfaces marked by giant current dunes 50 to 60 m above the
natural surface grade of Columbia River but below tops of sidestream delta terraces
(Qsdt) unmodified by floodwater; giant current dunes spaced 100 m or less; composed
of gravel similar to Qc except for rare boulders as large as 3 m; not overlain by lacustrine
sediment. Not everywhere distinguished from Qcgl

aif Gravel, undivided—Surfaces geomorphically similar to those of Qlfy but altitude similar to
both Qifo and Qify

Sand—Loose, medium to very coarse sand above level of Qifo; probably suspended load
of late flood(s)

Qsi Silt—Thinly and evenly to rhythmically bedded silt and very fine sand, evidently
polygenetic and in various stratigraphic positions: (1) overlies Qegu and Qcgl in the
Columbia River valley, (2) forms distinct terrace at altitude 275 m in canyon west of

1Numbers in brackets after place names refer to locations on figure 4, in pamphlet

Birch Flat [33], (3) occurs as discontinuous patches at altitudes below 275 m in lower
Wenatchee valley, and (4) overlies Qwtu near Monitor, where beds 0.3 m thick fine
upward from medium sand to clay

COLUMBIA RIVER FLOODS DEPOSITS—Divided into:

Gravel of lower-level bars—Similar to Qegu except that surfaces of bars are only 60 to 90
m above the river and embellished with giant current dunes spaced 100 m; surficial layer
of bar at mouth of Moses Coulee is redeposited Qme; great bar north side of Columbia
near Crescent Bar [44] contains rock types derived from upvalley,but long sweeping
foresets dip upvalley and material is sandy pebble gravel fining upvalley to medium
sand. Loess cap thinner than 0.5 m or is absent entirely. Not exclusively distinguished
from Qegu or Qcg

Miscellaneous gravel—Small patches at intermediate to low altitudes, probably mostly
contemporaneous with Qcg!

Deposits on upland surfaces—Sand and pebble gravel in discontinuous patches overlying
older surficial deposits or bedrock; extensive deposits on Babcock Bench [46] overlie
intricate scabland. Probably mostly contemporaneous with Qegu

Gravel of Moses Coulee floods—Along riverwise railroad near mouth of Moses Coulee, a
Poorly sorted boulder gravel almost entirely of basalt and displaying foreset bedding that
dips up Columbia River valley; between southern abutment of Rock Island Dam and
southern abutment of railroad bridge is moderately sorted pebble to basaltic granule
gravel displaying long foresets dipping gently upvalley; at Rock Island Dam, top of
deposit interbedded with and overlain by silt disconformably overlain by
Qcg!

Gravel of upper bar—Moderately sorted mixed-lithology cobble-to-boulder gravel
containing rare angular boulders as large as 2 m of Swakane Biotite Gneiss and quartz
diorite; internal structure is long downvalley-dipping foresets as tall as 15 m; shallow
moat at valley-side margin; surface near Pangbom airfield [38] 180 m above river level
displays giant current dunes spaced 215 m and whose lee slopes face downvalley;
maximum thickness of deposit 150 m or more. Mantled with 0.5 to 1.5 m of loess, Soil
contains neither textural B-horizon nor K-horizon, calcification being restricted to
overgrowths less than 1 mm thick on the undersides of stones

Qfg | GRAVEL OF FANCHER FIELD [37]—Cobble-to-granule gravel of rounded stones of
diverse rock types of Columbia River provenance; generally is moderately to well sorted,
lacks huge boulders characteristic of younger flood deposits but has thick crossbeds
dipping downvalley; to southeast contains much sand and granule gravel; capped by 0.5 to
2m ofcaliche that locally divides into multiple layers; caliche overlain by 1 to 3 m of loess;
forms extensive terrace at altitudes 410 to 435 m, 30 to 50 m above the altitude of
uncalichified gravel forming upper bars of Columbia River flood deposits (Qegu) farther
downvalley

Qisy | YOUNGER LANDSLIDE DEPOSITS—Angular debris from Yakima Basalt Subgroup;
overlies Qcg! but is partly eroded by younger floods

Qiso. | OLDER LANDSLIDE DEPOSITS—Hummocky diamicton underlying Qlfo, Qify, Qsa,
. Qegu, Qcg! and Qme; upper surface of toe of slide along and in Columbia River near
Malaga and Rock Island has high erosional relief, huge slide complexes on both sides of
Columbia River valley between Wenatchee and Rock Island Dam are sparsely strewn up
to altitude 325 m with very angular light-colored granodiorite boulders ice-rafted by great
floods. Landslide complex northeast of East Wenatchee consists near mountain front of
huge rotated, somewhat deformed blocks (Qisb) of the Grande Ronde Basalt and
Ellensburg Formation; to southwest is highly fractured deformed blocks and divided
debris of the Grande Ronde Basalt deposited in valleys cut into Wenatchee
Formation (Tw); east of river is thickly mantled with loess and eolian sand
Qwti_ | LOWER TERRACE GRAVEL OF WENATCHEE RIVER—Gravel similar to Qw but forming
terrace 10 m above modern flood plain; weathering and soil development very weak

Qtd | GRAVEL OF “d’’ TERRACE—Gravel similar to Qc but forming terrace 20 to 30 m above
Columbia River; unlike flood bars, terrace is flat and lacks giant current ripples, whaleback
form, and inner-margin moat; locally contains rare boulders as large as 0.8 m and grades
northward into surface clearly swept by floodwater; soil lacks B-horizon

GRAVEL OF **c TERRACE—Similar to Otd except forms two discrete terraces 45 m (Qtcl)
and 60 m (Qtcu) above Columbia River; in railroad cuts along southern side of Wenatchee
River overlies flood gravel containing angular boulders as large as 1.4m and displays crude
foreset beds dipping up Wenatchee valley; altitudinally related to Columbia-floods bars
Qegl and Qegu. Soil lacks B-horizon

G. R. Byerly, and R. D. Bentley
1982

GRAVEL OF “‘b” TERRACE—Small patch in Columbia River valley immediately upslope
~ from Qtc and lithologically like Qc; broader surface in lower Wenatchee valley is
lithologically like Qw; Wenatchee valley terrace 70 to 80 m above rivers and separated
from ‘‘c’’ terrace by abrupt scarp; includes 5- to 15-m mantle of very coarse to fine sand,
apparently backwash from floods along Columbia valley. Nowhere on surface of gravel or
on capping loess is soil redder than 10 YR or has textural B-horizon, nor does deposit
contain a buried paleosol
[/Gs4e))) sioeSTREAM DELTA-TERRACE—Angular to subrounded, poorly sorted gravel of clasts of
= Yakima Basalt Subgroup and interbedded arkosic sand; forms terraces at mouths of Rock

Island, Stemilt, and Squilchuck Creeks; internal structure in Stemilt Creek body is tall

foreset bedding dipping steeply toward the Columbia River, at Rock Island Creek, directly

overlies Qsi
SIDESTREAM TERRACE ALLUVIUM—Terrace of basaltic gravel, sand, and mud 5 to 7 m
above floors of Squilchuck Creek and lower Moses Coulee

UPPER TERRACE-GRAVEL OF WENATCHEE RIVER—Gravel identical to Qw but forms
Prominent terrace more than 40 m above Wenatchee River; soil on terrace lacks textural
B-horizon, and granodiorite stones are mostly fresh; unlike lower terrace (Qwtl), upper
terrace is extensively overlain by thin-bedded silt (Qsi)

[ewtus | UPPER SIDESTREAM TERRACE-ALLUVIUM—Alluvium of incised sidestream terrace that
is graded to incisec Qwtu mainstream terrace

| GRAVELLY SAND OF ‘a’ TERRACE—Poorly exposed fine to coarse sand, pebbly sand,
and sandy small-pebble gravel; pebbles are of locally derived Swakane Biotite Gneiss,
although deep cuts reveal a few clasts of granite of Columbia River provenance; forms
terrace in lower Wenatchee valley at altitude of about 320 m, separated from Qtb by
50-m-high scarp; capped by 1 to 3 m of massive silt containing rare angular pebbles of
leucocratic plutonic rocks and of Yakima Basalt Subgroup

Qs! | SAND, LOCALLY DERIVED—Loose very coarse to very fine sand arkose capping divide
between tributaries north of Wenatchee River; crossbeds and crosslaminations dip
southward; content of angular feldspar grains derived from tributary heads to the north;
deposit is as high as 60 m above gravelly sand terrace (Ata), which Qs! grades downslope
into or abuts

Faidy,})] DIAMICTON—Diamicton mainly of angular basalt clasts similar to units Tdyy and Tdyo,

albeit matrix is uncemented; only rarely contains very large entablature boulders;

deposited variously on minor divides and along modern stream valleys. Evidently formed

by debris flows guided by existing topography; mostly derived from Tdyy and Tdyo, but

near Mission Peak [30] derived directly from bedrock and is associated with large-block

landslides (Qlsb). Distinguished geomorphically from Tdyy and Tdyo but otherwise
indistinct from Qls and Qlso in area

HIGH GRAVEL OF WENATCHEE RIVER—Gravel identical to Qw except that unstable
and nondurable rocks (arkose, quartz diorite) are impoverished with respect to hard,
resistant rock types (quartz, amphibolite, dike rocks); caps knoll 130 m above Wenatc-
hee River; similar isolated deposits upvalley beyond map boundary occur on divides as
high as 525 m above valley floor

Tdyy | YOUNGER DIAMICTITE—Similar to Tdyo except that deposits occupy secondary divides
descending toward, but as much as 180 m above, modern drainages; rarely contains very
large entablature boulders; evidently derived from Tdyo. At and near Beehive Mountain, a
lateral ridge and moat separate unit from mounds of eroded Tdyo that protrude through
Tdyy as “‘islands”

OLDER DIAMICTITE—Diamictite of angular granule- to boulder-sized clasts of basalt;
largest unjointed clasts are unmodified prisms of colonade as much as 1 m in diameter, and
largest jointed clasts are of entablature to 20 m in intermediate diameter; the very large
clasts occur as isolated blocks or are clustered in irregular lenses to at least 300 m in
diameter and 80 m thick; rare angular deformed tabular blocks of the Ellensburg
Formation. Occupies divides descending toward the Columbia River valley parallel to
tributaries like Squilchuck and Stemilt Creeks,which have incised as deeply as 300 m into
bedrock, inverting the ancient topography; debris derived from Mission Peak area

BEDROCK

YAKIMA BASALT SUBGROUP OF THE COLUMBIA RIVER BASALT GROUP—Divided
into:
Wanapum Basalt—Includes:

[UHR] —iPrsiest Rapids Member—Fine- to medium-grained basalt flow with sparse plagioclase

and olivine phenocrysts less than 8 mm long. Intergranular to intersertal groundmass
texture. Reversed magnetic polarity. Occurs only in Kittitas Valley along Caribou
Creek

Roza Member—Fine- to medium-grained basalt flow with 5 to 10 percent plagioclase
phenocrysts but few glomerocrysts. Phenocrysts more than 5 mm long and uniformly
distributed throughout flow. Intergranular to intersertal groundmass texture.
Transitional magnetic polarity

Frenchman Springs Member—Two or more flows of fine- to medium-grained basalt.
Contains abundant to sparse plagioclase phenocrysts and glomerocrysts commonly 1
to 2 cm across, irregularly distributed throughout the flow. Lowest flow is generally
more highly porphyritic than overlying one and commonly has pillowed base. Normal
magnetic polarity. Includes the Ginkgo flow of Mackin (1961), which contains many
large plagioclase phenocrysts and glomeroporphyritic clots and the Sand Hollow flow
of Mackin (1961), which has few such phenocrysts and clots. West of long
120°07'30", a flow apparently more porphyritic than the Sand Hollow and less
porphyritic than Ginkgo forms lower flow in the member; may be one of the Kelly
Hollow flows of Bentley (1977) or an unusual facies of the Sand Hollow or Ginkgo
flows. Flows north of West Bar sparsely porphyritic except for a highly porphyritic flow
on Badger Mountain west of Rock Island Creek. Member is sparsely porphyritic where
exposed in fault blocks near Parke and Caribou Creek along east side of Kittitas
Valley. Locally includes the Vantage Member of Ellensburg Formation where Vantage
is too thin to show separately

Grande Ronde Basalt—Fine- to medium-grained basalt flows. Nonporphyritic to very
sparsely plagioclase porphyritic except unit Tgrp. Groundmass textures dominantly
intersertal with small clots of plagioclase and clinopyroxene. Complexly jointed. Pillows,
hyaloclastites, and invasive flows common. Locally includes thin sedimentary deposits
of Ellensburg Formation. Many flows in southeastern part of quadrangle display typical
jointing patterns including basal colonnade, central entablature, and, in some flows,
upper colonnade, all thoroughly described in nearby areas by Mackin (1961, p. 9-12),
Swanson (1967, p. 1083-1086), and Diery and McKee (1969, p. 52-54). Cliffs just east
of Crescent Bar [44] (studied by McDougall, 1976, p. 780, and Waters, 1961, p. 598)
and along most tributary canyons west of Columbia River show these features well
Jointing patterns in much of area are considerably affected by interaction of flows with
water and sediment. Subdivided on basis of magnetic polarity and locally distinctive
outcrop characteristics. Includes:

Upper flows of normal magnetic polarity—Subdivided into following units:

Basalt of Beaver Creek—Youngest flow in unit in northeastern part of mapped area.
Well-developed colonnade; pillowed base in places

Basalt of Keane Ranch—Several invasive flows and associated hyaloclastite and
Peperite. Includes flows of at least three different chemical compositions

Invasive flow of Duffy Creek—Shown only in extreme northeast corner of mapped
area

Tor: . Basalt of Rocky Point—Flow, possibly two flows in places, containing 2 to 5 percent

plagioclase phenocrysts less than 5 mm long. Lowermost flow in unit Tgn2, along

North Fork of Manastash Creek, consists largely of unsorted hyalociastite with

sand- to boulder-size fragments of broken pillows with or without glassy rinds.

Deposit is 10 to 15 m thick, unbedded, and locally contains intermixed sand.

Vertical dewatering conduits occur in places

Tgr2 Flows of reversed magnetic polarity—Subdivided into following units:

Invasive flow of Howard Creek (Howard Creek Member of Rosenmeier,. 1968, p.
22-25)—Upper contact is more complex than that of other invasive flows,
consisting largely of a thick hyalociastite and, locally, peperite. Well exposed 500 m
southeast of Grouse Spring [28] in upper part of Naneum basin and along the west
side of Diamond Head. Chilled sill-like contact against sedimentary rocks is exposed
locally, as along the road to Grouse Spring at elevation 1510 m

Invasive flow of Hammond—Same as Hammond sill of Hoyt (1961)

[Tont ] Lower flows of normal magnetic polarity—Occurs only along Naneum Creek and
contains at least two invasive flows
ELLENSBURG FORMATION—Includes:
(7) Volcaniclastic rocks—Mostly sandstone and siltstone but includes conglomerate,
diamictite of probable laharic origin, and very minor amounts of micaceous feldspathic
siltstone. Weakly lithified. Volcaniclastic detritus mostly andesitic and dacitic. Clasts
commonly pumiceous. Volcanic debris probably freshly erupted from volcanoes in
Cascade Range. Interbedded with and overlies Grande Ronde Basalt
Sandstone, siltstone, and conglomerate—Micaceous feldspathic sandstone, siltstone, and
very minor amount of pebble conglomerate and dark mudstone. Weakly indurated.
Interbedded with Grande Ronde and, locally, Wanapum Basalt. Includes:
Vantage Member—Occurs between Grande Ronde and Wanapum Basalts. Maximum
thickness about 30 m, average thickness 5 to 10 m. Pinches out toward Naneum Ridge
anticline

Tda | DIAMICTITE OF ANDESITE—Ciiff-forming massive diamictite north of East Wenatchee,
mostly angular porphyritic andesite to dacite clasts as large as 0.75 mset in a volcaniclastic
matrix. About 2 percent of gravel fraction is rounded—about 1 percent porphyritic
andesite and dacite and 1 percent vein quartz and various intrusive and metamorphic rock
types

HORNBLENDE ANDESITE PORPHYRY COMPLEX OF HORSE LAKE MOUNTAIN
(34]—Includes:

Homblende andesite porphyry—Gray, commonly with black shiny hornblende prisms to
several centimeters long; euhedral plagioclase and stubby pyroxene crystals in a dense
gray matrix which in some rock is crowded with microphenocrysts of plagioclase,
hypersthene, opaque minerals, and rare quartz and K-feldspar. Matrix is commonly
pilotaxitic to intersertal. Some rocks pervasively altered to chlorite, clays, zeolite, and
calcite. Includes masses of fine-grained slightly porphyritic to xenomorphic granular
Pyroxene gabbro altered to actinolite, clays, and calcite and rare muscovite. Sills
commonly about 10 cm to 15 m thick and with good columnar jointing (Bayley, 1965, p.
12-23)

(ae Breccia dike—Angular fragments less than one millimeter to several meters across of

sandstone, argillite, cumulative homblende gabbro, quartz diorite, and quartz gabbro in

a chloritic mesostasis with small plagioclase laths. Also contains abundant euhedral

hornblende phenocrysts to 6 cm long with abundant groundmass inclusions. Pilotaxitic

marginal phase similar to hornblende andesite porphyry (Thp) with only a few inclusions

Thd Area of numerous homblende porphyry andesite dikes and sills shown as overprint over
country rock. In Horse Lake Mountain summit area, dikes and sills make up more than
60 percent of terrain

Southwestern sequence
(eT) BASALT OF FROST MOUNTAIN [22]—Dense black microporphyritic olivine basalt;
microphenocrysts of plagioclase, clinopyroxene, and olivine in intersertal matrix of
plagioclase, clinopyroxene, opaque ore, and brown glass. Locally altered to siliceous white
rock. Locally columnar jointed

[Te | ANDESITE OF PEOH POINT—Gray to black homblende-hypersthene dacite porphyry;
holocrystalline—glomeroporphyritic fine-grained granular. Local crude columnar jointing
TANEUM ANDESITE—Mostly gray to green and brown, generally highly altered porphyritic
to nonporphyritic andesite, dacite, and rhyolite flows, tuffs, and breccia; greenish-blue,
purple, and white altered ash-flow tuffs, commonly welded, with relict quartz and
plagioclase phenocrysts

MANASTASH FORMATION—Sandstone, shale, and conglomerate. Light-greenish-gray or
tan, massive, medium- to coarse-grained feldspathic sandstone averaging 55 to 60 percent
quartz and 5 to 10 percent lithic clasts. Minor seams of bituminous coal; leaf fossils locally

Western sequence
ROSLYN FORMATION—Includes:

Upper member—Medium- to fine-grained, white-weathering to yellow, micaceous,
lithofeldspathic sandstone, some with calcite cement. Dark olive-gray to greenish-yellow
siltstone, predominantly quartz and feldspar; thin-bedded to laminated. Subordinate
0.6- to 6-m thick seams of well-jointed, banded bituminous coal. See “Coal Measures”
of Bressler (1951, p. 31)

Middle member—Similar to upper member (Tru) but only very minor stringers of coal

Lower member—Mostly white, weathering to yellowish and pale orange, medium- to
coarse-grained, micaceous, in part zeolitic, lithic, feldspathic, and lithofeldspathic
sandstone with crossbedding, pebble stringers, and cut-and-fill structures in beds to 15
cm thick. Abundant conglomerate and pebbly sandstone with rounded pebbles of
granitic and aphanitic extrusive or hypabyssal rock. Includes Bressler’s (1951, p. 35)
basal beds of red to red-brown fine-grained sandstone with minor angular clasts of
quartz, metamorphic rock fragments, some feldspar, and other rocks. Some sandstone
with abundant calcite

RHYOLITE—Includes:

Trhf Rhyolite flows, tuff, and tuffaceous shales; some interbedded sandstone—Flows are white
thyolite weathering irregularly to brown and yellow. Commonly poorly exposed. Earthy
or finely granular by spherulitic devitrification. Microphenocrysts of quartz and
plagioclase in mesostasis of very fine-grained quartz, plagioclase, K-feldspar, sericite,
hematite, and chlorite; rare plagioclase microlites. Clayton (1973, p. 29) reports
sanidine phenocrysts and a SiO, content greater than 80 percent. Light-brown
interbedded tuff and shales with volcanic clasts of rhyolite or altered rhyolite as above
[teni] Rhyolite dikes and plugs—Similar to extrusive rhyolite but appears to crosscut structure

and lacks sedimentary interbeds

[UGB teanaway wasat—Bosalt, basaltic tuff, and breccia with minor anceste, dacite, and
rhyolite. Black, generally dense to glassy nonporphyritic pyroxene and rare olivine basalt,
weathering red brown to yellow. Commonly fine-grained intersertal with plagioclase laths
and clinopyroxene; interstices of brown glass or alteration products (Clayton, 1973, p.
18-19). Blocky to columnar-jointed flows characterized by large chalcedony and calcite
amygdules. Tuff and breccia commonly altered to clays. Siliceous varieties including
welded tuff are white, purple, and highly altered but contain relict phenocrysts of quartz,
plagioclase, and rare K-feldspar

aw SWAUK FORMATION—Relatively dark gray weathering to tan, zeolitic, and locally calcic
micaceous feldspathic to lithofeldspathic sandstone averaging about 35 to 40 percent
quartz and 15 to 20 percent lithic clasts, 65 percent volcanic rock. Thin to very thick
bedded, poorly sorted, locally crossbedded with lesser amounts of carbonaceous siltstone
and shale, pebbly sandstone, light-colored micaceous sandstone, and conglomerate

Arkosic sandstone facies—White feldspathic sandstone, similar in appearence to
sandstone of Chumstick Formation (Tc), poorly sorted, thick-bedded, and crossbedded.
Interbedded with shale (Tssh)

Shale facies of Tronsen Ridge—Evenly and thinly bedded, locally crossbedded, relatively
dark grayish or tannish micaceous lithofeldspathic sandstone, alternating with evenly
bedded dark carbonaceous siltstone and shale. Light-colored, finely laminated,
fine-grained sandstone and siltstone without crossbedding and lesser amounts of
thick-bedded and crossbedded sandstone and pebble conglomerate

ee] Conglomerate facies—20 to 50 percent conglomerate and conglomeratic sandstone in
feldspathic and lithofeldspathic sandstone, siltstone, and shale. In vicinity of Scotty [8]
and Ruby [4] Creeks, boulders to pebbles of chert, argillite, granitic and metamorphic
rock in matrix of micaceous lithofeldspathic to feldspathic sandstone, crossbedded with
cut-and-fill structures. In the vicinity of Mission Peak [30] and Mount Lillian, pebbles are
predominantly light-colored volcanic rocks

Monolithologic fanglomerate facies—North of Shaser Creek [7], mostly rounded clasts of
serpentinized peridotite in serpentinite sand matrix; contains beds of ironstone (see
Lamey, 1950). In the Leavenworth fault zone north of Tronsen Creek and north of Red
Hill [9] fanglomerate is made of subangular to rounded granodiorite in angular
granodiorite sand. Locally strongly sheared

Tsir Ironstone—Iron-rich sandstone, shale, and conglomerate, locally well bedded. Iron

sese minerals are limonite, hematite, and magnetite. Conglomerate composed of peridotite
and serpentinized peridotite in iron-rich matrix. Most deposits are rich in nickel
(Broughton, 1944; Lamey, 1950)

[78 | SILVER PASS VOLCANIC ROCKS OF FOSTER (1960)—Mostly discontinuous beds of
mafic tuff and breccia interbedded in Swauk Formation, dark-yellowish-green and
containing altered mafic microporphyry-bearing plagioclase, homblende, and pyroxene.
Alteration minerals are calcite, smectite, chlorite, epidote, and zeolite. Major outcrop area
west of Swauk Pass is interbedded altered tuffs and arkosic sandstone. Probable Silver
Pass shown on north side of South Cle Elum Ridge is poorly exposed, altered, sheared,
and locally recrystallized silicic tuff and breccia

Eastern sequence (Chiwaukum graben)

Tw WENATCHEE FORMATION—Lower half predominantly bluish-gray, muscovite-bearing
and, in places, tuffaceous shale and siltstone with interbed of friable limonitic quartz
sandstone. Red oxidized zones in upper part of lower shale. Overlain by crossbedded
quartz sandstone, beds 5 to 15 m thick, in turn overlain by thinly laminated
light-gray-weathering to yellowish-brown shale, grading upward into similarly colored
sandstone with little muscovite but otherwise similar to lowermost sandstone interbeds.
Quartz clasts in sandstone are typically angular to subangular. Uppermost part is
conglomerate, made of rounded to subrounded clasts of felsic volcanic rocks and some
vein quartz and chert in a friable feldspathic sandstone matrix with appearance of an
arkose in which feldspar has altered to clay. Soils developed on shales are clay-rich and
characteristically expand to a popcorlike texture. South of Malaga, similar to quartz-rich
sandstone and red and green shales of type Wenatchee. Near Lion Rock is green and
yellow to white dacitic to rhyolitic lapilli tuff and breccia composed of altered glass shards;
locally strongly eutaxitic with microphenocrysts of plagioclase and quartz. Similar tuff
exposed on old State Highway 97 east of Swauk Prairie [13] is interbedded with
coarse-grained tuffaceous arkose. Locally contains carbonized wood. Where exposed
along highway 970 unit is red, green, and brown shale, and orange clayey feldspathic
sandstone and may be part of large Lookout Mountain [14] landslide

CHUMSTICK FORMATION—Includes:

Te Sandstone, shale, and conglomerate—White, locally gray, medium- to coarse-grained,
micaceous feldspathic sandstone averaging 35 to 40 percent quartz and 10 to 15 percent
lithic dasts, 90 percent volcanic rock. Crossbedded and channeled, interbedded with lesser
amounts of thin pebbly sandstone and green to bluish shale

Ten Shaly unit of Nahahum Canyon—Shaly sandstone and shale with thin bedding accented
by thin laminae of biotite and organic matter. Some thin turbidite beds. Grades laterally
into unit Tc

Tete Tuff of Eagle Creek—Coarse-grained light-greenish-gray tuff with pumice clasts and flakes
of carbonized wood; equals Tt1 of Whetten and Laravie (1976). Tuff in upper East Fork
of Mission Creek correlated on basis of lithology

Teteb Tuff of Cashmere (b)—Coarse-grained dense pumiceous vitric tuff. Thickness variable to 3
m. Continuous with tuff (Tt2) in Cashmere quadrangle (Whetten and Waitt, 1978)

Tuff of Cashmere (a)—Dense fine-grained, crystal vitric tuff, 2-4 m thick. Continuous with
tuff (Tt1) in Cashmere quadrangle (Whetten and Waitt, 1978)

Red conglomerate—Massive red to purple and green conglomerate in beds 6 m thick with
1- to 2-m thick dark-colored sandstone interbeds. Clasts are quartz diorite, phyllite and
chert, as in other conglomerate, and amygdaloidal basalt and rhyolite

Fanglomerate and monolithologic fanglomerate—tIn vicinity of Peshastin Creek,
monolithologic fanglomerate made of well-rounded cobble- to small-boulder-size clasts
of serpentinized peridotite in green to rusty brown matrix (Cashman, 1974, p. 12)
interbedded with angular to subangular clasts of quartz diorite to 1 m in size in angular
unsorted matrix of quartz diorite to granodiorite sand. In Mission Ridge area, quartz
diorite to granodiorite material only

Basalt, basaltic breccia, and tuff—Black to dark-brown and gray to green dense basalt and
amygdaloidal basalt; flows(?) and clasts in basaltic sand matrix. Some clasts of indurated
feldspathic sandstone. Crudely bedded and locally interbedded in feldspathic sandstone
of unit Te

Small Tertiary intrusive bodies
[Tima | MISCELLANEOUS DIKES, SILLS, AND PLUGS—Individual intrusive masses and areas
intruded by numerous dikes and sills, generally more than 50 percent of terrain. Mostly
andesite but ranges in composition from diabase to dacite and rhyolite (Gresens, 1976),
generally considerably altered. An intrusive dacite dome on the south side of Dry Gulch
[36] has a partial shell of perlite and breccia. Core is porphyritic xenomorphic with broken
quartz phenocrysts or xenoclasts (Coombs, 1952, p. 198-199)

CAMAS LAND DIABASE OF SOUTHWICK (1966)—Dark-brown to black diabase and
gabbro weathering to pale gray. According to Southwick (1966, p. 5-8), most of the rock is
coarse-grained ophitic diabase with normally zoned labradorite to andesine, subcalcic
augite, and pigeonite. Marginal phases contain olivine and have intergranular and
intersertal groundmass. Alteration is slight

Saas DIABASE, GABBRO, AND BASALT—Fine- to medium-grained black diabase and gabbro
weathering to brown and reddish brown. Contains labradorite, clinopyroxene, rare
olivine, and opaque ores. Subophitic to ophitic texture; variously altered to smectites,
calcite, and chlorite (Stout, 1961, p. 350)

TEANAWAY DIKE SWARM—In the area of the Teanaway dike swarm, density of dots
represents proportion of terrain underlain by dikes. Dikes are mostly dark green and brown
to black basalt and diabase weathering reddish brown. Includes pale, dull holocrystalline
dikes with plagioclase laths and granular clinopyroxene in intergranular texture. Interstices
are filled with quartz, plagioclase, zeolite, and clays (Southwick, 1966, p. 9). Waxy, partly
glassy dikes with andesine, clinopyroxene, and minor olivine; altered to chlorophaeite and
devitrified glass (Southwick, 1966, p. 10-11)

HYPERSTHENE GABBRO—Heterogeneous fine- to medium-grained gabbro with
hypersthene and clinopyroxene commonly altered to pale-green amphibolite and clays.
Calcic plagioclase is rimmed with graphic intergrowths of albite(?) and K-feldspar and
feldspar and quartz. Locally brecciated and mylonitized

Pre-Tertiary basement
ROCKS OF THE MOUNT STUART BATHOLITH—Includes:
Biotite-hornblende-quartz diorite—Medium-grained hypidiomorphic granular; massive to
strongly gneissic near margins of pluton. Includes some granodiorite

Biotite-hornblende granodiorite—Medium-grained hypidiomorphic granular. Massive to
weakly gneissic in area of Enchantment Lakes, rich in mafic inclusions. Near summit of
Mount Stuart cut by aplite and pegmatite dikes and contains vuggy feldspar clots and
radial bursts of tourmaline

Granodiorite metaporphyry and metaquartz diorite—Similar to metaporphyry in contact
complex, but nonschistose

Contact complex—Mostly hornblende and biotite schist, gneissic leucoquartz diorite,
schistose hornblende-biotite granodiorite metaporphyry with minor serpentinite,
altered; as much as 10 m thick, trending mostly northwest. Some rocks thermally
metamorphosed. Probably related to metaporphyry in unit Kmsm

Kmsd, Homblende feldspar dacite and granodiorite dike complex (diagonal line overprint on
other units) —Fine-and medium-grained homblende feldspar dacite porphyry and
medium-grained hornblende biotite granodiorite dikes, commonly altered; as much as
10 m thick, trending mostly northwest. Some rocks thermally metamorphosed.
Probably related to metaporphyry in unit Kmsm

sg SWAKANE BIOTITE GNEISS—Fine- to medium-grained biotite-plagioclase-quartz gneiss;
commonly granoblastic and locally strongly cataclastic to mylonitic, with varying
amounts of muscovite and garnet and small amounts of sphene, zircon, apatite, and
magnetite (Waters, 1932, p. 615). Amphibolite, homblende schist, and calc silicate
schist locally. Alaskite and pegmatite dikes and sills

INGALLS TECTONIC COMPLEX—Includes:

Silicate carbonate rock—Bright orange craggy masses of silica, calcite, and magnesium(?)
carbonate derived from alteration of serpentinite along faults. Locally, small patches of
garnierite, hence called nickel dikes (Pratt, 1958, p. 164-165; Miller, 1975, p. 32-33)

Amphibolite and schistose amphibolite—Very fine grained massive to weakly foliate
amphibolite; minor epidote minerals, biotite, opaque ores, and sphene. Probably
metamorphosed Hawkins Formation (Smith, 1904, p. 4) or sheared and recrystallized
gabbro or diabase

Horblende schist, schistose amphibolite, and lesser amounts of mica schist—Mostly very
fine grained actinolitic hornblende and homblende plagioclase schist; locally, cordierite
biotite schist, garnet biotite schist, and small pods of serpentinized peridotite. Probably

more thoroughly metamorphosed greenstone and associated sedimentary rocks of the
Hawkins Formation. Probably includes metamorphosed Peshastin Formation

Diabase and gabbro—Mostly highly heterogeneous uralitized pyroxene gabbro and
diabase ranging from hypidiomorphic granular to ophitic or diabasic. Southwick (1974,
p. 398) reports anorthite in the least-altered anorthositic varieties. Shearing and
brecciation is common with recrystallization to weakly foliate amphibolite. Layered
structure is uncommon; cumulate textures are lacking in eastern part (Southwick, 1974,
Pp. 98) but present in the western part (Miller, 1975, p. 42). Esmeralda Peaks[5] and
Hawkins Mountain are mostly diabase

Foliated and massive serpentinite, serpentinized peridotite, and metaserpentinite and
metaperidotite—Prior to serpentinization, ultramafic rocks were mostly harzburgite,
with minor wehrlite and dunite (Southwick, 1974, p. 397). South of the Stuart Range,
harzburgite (shown without shearing symbol) is characterized by spinel foliation and
some compositional layering including chromite pods and layers. A relatively
unserpentinized block of hornblende-bearing lherzolite (shown without shearing
symbols) lies west of Mount Stuart (Miller and Frost,1977,p. 284, Cowan and Miller,
1980, p. 2). In an irregular aureole around Mount Stuart batholith, ultramafic rocks are
commonly thermally metamorphosed to talc-tremolite and anthophyllite rocks, all
bearing newly formed forsterite and characteristically orange weathering and blocky
jointed (Miller, 1975, p. 33; Frost, 1973b). West and southeast of Mount Stuart areas of
strongly sheared serpentinite (shearing symbols) from Cowan and Miller (1980, p. 2)

Metabasalt (greenstone), tuff, and breccia—Predominantly massive greenstone with
lesser amounts of metabreccia and tuff, mostly in greenschist facies: Hawkins Formation
of Smith (1904, p. 4). Breccias contain metamorphosed andesite or keratophyre
(Southwick, 1974, p. 395-396). Locally includes fine-grained amphibolite and
metadiabase

Argillite, phyllite, sandstone, metasandstone and conglomerate, metamorphosed flows
and breccias, and minor chert and marble—Predominantly black hackly argillite to slaty
argillite with subordinate very fine grained, angular, poorly sorted dark lithic
subquartzose sandstone with graded beds, local rhythmite. Subordinate volcanic-lithic
microbreccia and small pebble conglomerate. Red, gray, and black radiolarian chert
and metachert. Dacitic to andesitic tuffs, breccias,and flows, mostly metamorphosed,
minor on east (Southwick, 1974, p. 395), more abundant in De Roux Creek area (Miller,
1975, p. 6). Locally includes very fine grained amphibolite, cordierite-biotite schist, and
calc-silicate granulite. Includes most of Peshastin Formation of Smith (1904, p. 3-4)

LOW-GRADE METAMORPHIC SUITE—Includes:
Greenschist—Very fine grained epidote-chlorite-quartz schist with varying amounts of
crossite. Relict pillow structure in greenschist northwest of Keenan Meadows [23].

Includes pegmatitic biotite gneiss, homblende gabbro, and quartz plagioclase gneiss
west of Buck Meadows

Phyllite—Dark graphitic albite-muscovite-quartz phyllite grades into fine-grained mica
schist. Includes minor greenschist and blue amphibole schist and pods of metagabbro.
Well-developed cleavage, crinkled, and isoclinally folded



Table 1.— Samples dated by fission-track and isotope analysis

[All fission-track ages calculated with Af=7.03 x 10-7 yr-*; all USGS K-Ar ages calculated on the basis of 1976 IUGS decay and
abundance constants. Ages from Gresens corrected by use of table in Dalrymple (1979)]

Field
Map sample Location
no. no. Method = Materials LatN. — Long W. Unit or formation (m. y.) ‘Comments Source
1 «P41 UPb = Zircon 47°27.9' = 120°40.4" Ingalls Tectonic Complex Late Jurassic Southwick, 1962
2. RWT 55-76 K-Ar Homblende 47°28.0' = 120°39.1' do. 85.3+1.8 Thermal metamorphic This report
event; metadiabase
3. RWT-512-75 FT Zircon 47°14.6" 120°41.8" Silver Pass Volcanic 49.125.2 C. W. Naeser,
Rocks of Foster (1960); written commun.,
interbed in Swauk Formation 1976
4. VF-77-101 FT Zircon 47°20.4" 120°35.8" do. 50.521.2 This report
5. ER-76-75 FT Zircon 47°20.1' —-120°42.0" do. 43.6+1.1 Age appears to be This report
too young
6. VF-76-450 FT Zircon 47°20.5' 120°38.9" do. 48.642.3 This report
7. RWT-400.-76 K-Ar Whole rock  47°23.8’ ——:120°40.1' Basalt in Teanaway dike 46.420.4 -100+200 mesh This report
swarm 46.920.6 -60+100 mesh,
acid treated
8. KAS K-Ar Whole rock  47°25.0' —-120°23.1'_—_—Diabase dike intruding 47.1228 R. L. Gresens,
Chumstick Formation written commun.,
1979
9. RWT-66-77 K-Ar —_ Biotite 47°17.7" 120°23.8" Chumstick Formation 46.323 Minimum age of This report
source; granodiorite
boulder in fanglo-
merate in Leavenworth
fault
10. RS FT Zircon 47°19.9" 120°48.7' Rhyolite pumice 55.323.0 Probably con- J. A. Vance and
lapilli tuff taminated with older C. W. Naeser,
zircon written commun.
1976
i. RT FT Zircon 47°18.9' —_120°48.4’ __Rhyolite dike in Teanaway 20.0208 J.A. Vance and
Basalt C. W. Naeser,
written commun.,
1976
12. VF-77-184 K-Ar —_Biotite 47°25.5' 120°19.3' Dacite intrusive dome in 43.220.4 This report
Chumstick Fm.
13. KA-6 K-Ar —_Biotite 47°23.7' 120°19.3' do. 42.5216 R. L. Gresens,
written commun.,
1979
14. R-90 FT Zircon 47°25.5' =: 120°19.3" do. 51.422.8 Age is too old; J. A. Vance and
contamination? C. W. Naeser,
written commun.
1978
15. RWT 4690-76 FT Zircon 47°02.1' 120°56.1' Taneum Andesite 46.2+1.1 Age appears to be This report
too young
16. VF-77-305 FT Zircon 47°02.1' 120°56.1" do. 51.821.0 This report
17. RWT-435-76 K-Ar Whole rock —47°03.9'—-120°59.6" Basalt of Frost Mtn 32.220.4 —60 mesh; This report
minimum age?
18. RWT-349-76 K-Ar Whole rock 47°17.5' ~—:120°23.5'—_ Basalt dike or sill in 32.1+0.7 —60 mesh; This report
Swauk Formation minimum age?
19. R42 FT —ireon 47°16.8' —120°35.8’_Tuff bed in Wenatchee(?) 34.4223 4. A. Vance and
Formation Cw.
written commun.
1978
20. RWT-644.77 FT Zircon 47114 120°42" do. 32.820.6 This report
21. VF-77-149 FT Apatite 47°20.5' 120°14.6" do. 35.6220.3  U concentration This report
very low
22, LS 6C FT Zircon 47°23.2' —120°20.1' _—_Tuff bed in Wenatchee 33.4214 R. L. Gresens,
Formation C. W. Naeser,
J.T. Whetten,
written commun.,
1978
23. MS 4C FT Zircon 47°23.2' = 120°20.1" do. 49.1+2.3 Contaminated (?) R. L. Gresens,
with older detridal C. W. Naeser,
zircon J. T. Whetten,
written commun.,
1978
24. 27a FT Zircon 47°28.6' = 120°17.6" do. 34.521.2 R. L. Gresens,
C. W. Naeser,
J. T. Whetten,
written commun.
1978
27a 1G Apatite 47°28.6' —120°17.6" do. 39.829.0 R.L. Gresens,
C. W. Naeser,
J. T. Whetten,
written commun.,
1978
25. RWT-318-76 K-Ar Homblende  47°24.2' —_120°26.5" Dike in complex of Horse 25.120.3 This report
Lake Mountain
26. RWT-316-76 K-Ar Homblende  47°25.0' —120°26.0' do. 29.826.6 This report
27. KA-1 K-Ar Homblende = 47°24.8' —-120°26.7" do. 30.222.1 R. L. Gresens,
written commun.,
1978
28. KA-2 K-Ar Homblende 47°23.5' ——-120°25.7' do. 29.723.2 R. L. Gresens,
written commun.,
1978
29. KA3 K-Ar Homblende 47°25.3' —- 120°22.8’ Andesite dike in misc. 35.123.2 Probable minimum R.L. Gresens,
dike unit Tmd age written commun.,
1978
30. 5-Porter-U.W FT Zircon 47°04.9' —120°39.9' Tuff in Thorp Gravel 3.720.7 S.C. Porter and
C. W. Naeser,
written commun.,
1976
31. RBW-75-410 FT Zircon 47°06.6' 120°40.9" do. 3.820.3 Waitt, 1979
32, RBW-77.988 FT Zircon 47°05.8' = 120°40.3' do. 4.420.3 This report
33, RBW.77.988 K-Ar Homblende 47°05.8’ —_120°40.3" do. 4520.7 This report