Late Cenozoic Deposits, Landforms, 

Stratigraphy, and Tectonism in 

Kittitas Valley, Washington

Late Cenozoic Deposits, Landforms, 

Stratigraphy, and Tectonism in 

Kittitas Valley, Washington

By RICHARD B. WAITT, JR.

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1127

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress catalog-card No. 79-600011

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-03147-7
CONTENTS

Page

Abstract---------------------------------------------------------—----- 1

Introduct ion---------- — --_-__--_-_--__----_--_-__------_--------------- 1

Grande Ronde Basalt of Yakima Basalt Subgroup----------- — ---- — - — ----- 1

Ellensburg Formation----—---------------------------------------------- 1

Surficial Deposits and landforms---------------------------------------- 3

Depositional facies--------------------------------------------------- 3

Criteria for subdivision--——___________________-__-_---------_------ 7

Nomenc1ature--------------------------------- — _______________-_----__ 7

Correlation of surfaces and deposits---------------------------------- 9

Alluvium and drift---------------------------------------------------- 9

Thorp Gravel------------------- —— --- —— -- —— -- —— ------ —— --- —— -- 9

Lookout Mountain Ranch Drift-------------------—----—------------- 12

Kittitas Drift ———— ———— ——————————————— ————— —————————— 13

Lakedale Drift-- ————— ———————— —————— ———— --———————————— 13

Holocene alluvium--------------------------------------- — ---------- 13

Comparison to glacial sequence and chronology of Sierra Nevada-------- 13

Structure---------------—--—-_-__-__--_-__-__--_____------------------ 14

Folds —— ———————— ———————— ———————————— ————— ———— ———— —— 14

Faults-- ——————————————— ————— ——————— -- ———— ———— —— ————— 15

Post-Yakima faults in central Washington----------—---------------- 15

Young faults in Kittitas Valley-----------------------—------------ 15

Regional tectonic significance--------- — ----------------------------- 15

Acknowledgment---------- — ____-_-_-_-__-_-__ — ___________________--_---- 16

Reference cited------------------------------—------------------------- 16

ILLUSTRATIONS

Page

Figure 1. Tectonic map of south-central Washington————— —— ———— ——————————————————————————————— 2

2. Geologic map of Kittitas Valley area-------—----------------------------------------------------- 4

3. Diagram showing nomenclature and age of Yakima Basalt Subgroup-——------------------—————_____ 7

4. Geologic map of northern Kittitas Valley---- ———— - —— —— -- —— --------- —— —— _______ ——— __ —— ____ g

5. Composit section of Thorp Gravel-----------—_--_-__---_-_--_____-___----------------—-—-------- 10

TABLES

Page

Table 1. Nomenclature of surficial deposits----------------------------------------------------------------- 9

2. Fission-track ages of Thorp Gravel-——________________________________————__________————___ n

3. Correlation of surficial deposits of Kittitas Valley with Sierra Nevada—————— —————————— ——— 14

LATE CENOZOIC DEPOSITS, LANDFORMS, STRATIGRAPHY, AND 

TECTONISM IN KITTITAS VALLEY, WASHINGTON

By Richard B. Waitt, Jr.

ABSTRACT.--Kittitas Valley, a structurally determined 

wide segment of the Yakima River valley, is partly 

filled with the Pliocene Thorp Gravel and with Pleistocene till, outwash, and related sediment that accumulated during three glaciations. The Thorp Gravel, 

whose age according to fission-track dating is about 

3.7 m.y., forms a conspicuous fill terrace locally as 

high as 130 m. Bodies of drift, all younger than the 

Thorp Gravel, form nested fill terraces along the Yakima River. The massive moraines, intermediate morpho-stratigraphic position, and well-developed soil of 

the Kittitas Drift suggest its correlation with the 

penultimate northern-hemisphere glaciation of about 

0.13 m.y. ago. The Lakedale Drift, which composes a 

single outwash terrace in Kittitas Valley, evidently 

correlates with the classical late Wisconsin Glaciation. The newly named Lookout Mountain Ranch Drift, 

which forms moraines at higher altitudes than and is 

older than the Kittitas Drift, lacks an attendant 

valley train.

Three faults disrupt the Thorp Gravel but apparently not the Kittitas Drift, and therefore probably are between 0.13 and 3.7 m.y. old. The eastward trend and up-to-the-basin throw of the faults 

probably reflect reverse faulting due to a regional 

north-south compression that uparched several easttrending anticlines in central Washington. The 

southeast trend of the dextrally echelon arrangement 

of the faults apparently is due to a right-lateral 

couple across a zone parallel to the Olympic-Wallowa 

lineament.

INTRODUCTION

Kittitas Valley, an unusually wide segment of the 

Yakima River valley near the western edge of the Yakima Basalt Subgroup, is the topographic expression of a 

broad synclinal basin in the Yakima Basalt Subgroup 

and the Ellensburg Formation (figs. 1 and 2). Containing the most complete Pliocene and Pleistocene record in the eastern Cascades and lying parallel to and 

immediately north of the Olympic-Wallowa lineament as 

defined by Raisz (1945), the valley is a likely area 

in which to examine Pliocene and Pleistocene tectonism 

in the region.

Since the early reconnaissance of Russell (1893, 

1900) and early mapping by Smith (1901, 1903a, 1904), 

who dealt with the Quaternary but casually, only 

Porter (1975, 1976) has scrutinized the Pleistocene 

record in upper Yakima Valley. The present report 

augments the investigations of Porter and evaluates 

Pliocene and Pleistocene tectonism in and beyond 

Kittitas Valley.

GRANDE RONDE BASALT OF 

YAKIMA BASALT SUBGROUP

The geochemical, petrographic, and megascopic 

character of the laterally continuous basalt flows peripheral to Kittitas Valley indicate their stratigraphic position low in the Yakima Basalt Subgroup, below 

the Vantage Sandstone Member of Mackin (1961) 

(Rosenmeier, 1968; Tabor and others, 1977; Bentley, 

1977; D. A. Swanson, oral and written commun., 1978) 

(fig. 3). The basalt is thus part of the Grande Ronde 

Basalt of Swanson and others (1977). The absence of 

post-Vantage basalt in western Kittitas Valley is consistent with the absence of the younger formations of 

the Yakima Basalt Subgroup near the western margin of 

the basalt field farther south (Waters, 1955; Mackin, 

1961; Swanson, 1967; Swanson and Wright, 1978).

ELLENSBURG FORMATION

Conformably underlying, interlayered with, and 

conformably overlying the Grande Ronde Basalt are volcaniclastic sedimentary rocks that range from siltstone to cobble conglomerate, the latter comprising 

silicic to intermediate volcanic clasts. The lowest 

of the volcaniclastic strata, which crops out at the 

base of the Grande Ronde Basalt in the Yakima River 

canyon south of Lookout Mountain, includes fluvial 

conglomerate similar to that characteristic of the 

thick suprabasalt beds, in which some fluvially rounded boulders exceed 35 cm and whose diamictites contain 

rare clasts as large as 2.3 m. Although most of the 

sedimentary rocks are moderately sorted plane-bedded 

and crossbedded alluvium, several massive diamictite 

units as thick as 6 m in the suprabasalt strata apparently originated as lahars (Schmincke, 1967b). Crossbedding in sandstone and imbrication in conglomerate 

in western Kittitas Valley indicate variable paleocurrents, mostly toward the northeast, east, and 

southeast, down the regional eastward paleoslope envisioned by Waters (1955) and Schmincke (1967a).

Russell (1900) noted the volcaniclastic sandstone 

beds at the base of the basalt on Lookout Mountain, 

but did not include them within the Ellensburg, which 

he and Smith (1901, 1903a) defined as strictly overlying the Yakima Basalt Subgroup (then, Yakima Basalt) 

in the area. The interbasalt and subbasalt sedimentary strata on Lookout Mountain and vicinity, however, 

apparently are everywhere conformable with the basalt. 

And in color, mean and maximum grain sizes, sorting, 

bedding, lithology, and lithification they are similar 

to the sedimentary beds overlying the basalt, but in 

all these respects differ from the unconformably underlying Eocene arkosic sedimentary rocks farther

1
LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

121° 120° 119°

KILOMETERS

Figure 1. Tectonic map of south-central Washington, 

showing Olympic-Wallowa lineament, major anticlines and faults in the Yakima Basalt Subgroup, 

the Hog Ranch axis of Mackin (1961), and western 

limit of the Yakima Basalt Subgroup. C, Cle Elum; 

E, Ellensburg; LM, Lookout Mountain; T, Thorp; 

WG, Wallula Gap; Y, Yakima. Anticlines plunge 

generally eastward from the Cascades and westward 

from the Hog Ranch axis; the Yakima River thus

crosses the several anticlines south of Ellensburg generally along a cross-structural sag. The 

Kittitas Valley faults are en echelon to each 

other and to anticlines and attendant compressional faults to the southeast. Data from Mackin 

(1955), Newcomb (1970), FUGRO (1974), Tabor and 

others (1977), Bentley (1977), and R. D. Bentley 

(oral commun., 1977).
SURFICIAL DEPOSITS AND LANDFORMS

EXPLANATION

Younger volcanic rocks

covering Yakima Basalt

Subgroup

Contact, approximately located

Western limit of Yakima Basalt

Fault scarp in Kittitas Valley 

Hachures on downfhrown side

Reverse fault in bedrock 

Bar and ball on downfhrown side

Anticlinal crest, showing plunge

Prominent ridge, 

probably northwest extension of anticline

Regional arch

northwest. Evidently all of the volcaniclastic sedimentary beds conformably with the basalt are genetically and temporally related, and they collectively 

compose a unique, mappable body of rock.

Regionally, the base of the sediment-rich part of 

the basalt-volcaniclastic section rises in stratigraphic position southeastward. Mackin (1961) defined 

the base of the Ellensburg in the Vantage-Priest 

Rapids area fairly high in the section, at the top of 

the Wanapum Basalt of Swanson and others (1977). 

Smith (1903a), Waters (1955), and Schmincke (1964), 

however, included the interbasalt sediment as far down 

in the section as the base of the Wanapum, in the 

Ellensburg Formation. Schmincke (1964, 1967a, 1967c) 

also redefined the Ellensburg as mutually interfingering with the Wanapum and Saddle Mountains Basalts, a 

practice adopted by Bingham and Grolier (1966) and by 

more recent workers. In western Kittitas Valley the 

sedimentary strata intercalated with and underlying 

the Grande Ronde Basalt show that the mutually interfingering relation of the two lithosomes--westwardtonguing basalt and eastward-tonguing silicic volcaniclastic sedimentary rock--extends to the very base 

of the Yakima Basalt Subgroup. The interbasalt sedimentary strata are distinguishable from each other and 

from the suprabasalt Ellensburg strata only because of 

the intervening basalt members. As indicated by figures 2 and 4, I therefore opine that all of these conformable, sedimentologically related strata in the 

Kittitas Valley area be included within the Ellensburg 

Formation, and that the definition of the Ellensburg 

be extended stratigraphically downward to the base of 

the basalt-sedimentary sequence. A precedent for this 

type of definition is Griggs 1 (1976, p. 6) exclusion 

of sedimentary interbeds from the Yakima Basalt Subgroup and his assignment of them to the Latah Formation, which he redefined as mutually intertonguing 

with the Grande Ronde and Wanapum Basalts.

The Ellensburg strata overlying the basalt near 

the margin of the basalt field are relatively thick 

because they are not punctuated by the younger basalt 

members, which, offlapping eastward, failed to gain 

the western margin of the field. The frequency of basalt eruption, moreover, generally decreased between 

the earlier (16.5 to 14 m.y.) and later (12 to 6 m.y. 

ago) periods of the basalt eruption (fig 3; McKee, 

Swanson, and Wright, 1976). Consequently, the silicic 

volcaniclastic debris, even if supplied at a constant 

mean rate throughout Yakima time, should have built 

fans that were thicker and extended farther eastward 

in Saddle Mountains time than in Grande Ronde time, 

thus making the upper part of the basalt-sedimentary 

suite particularly rich in sediment, especially in the 

western parts of the basalt field.

In the western areas the suprabasalt volcaniclastic beds overlie only the Grande Ronde Basalt: there 

is no guarantee that the top of the Ellensburg in 

western Kittitas Valley is as young as the base of 

what Mackin (1961) defined as Ellensburg farther east. 

From such exposures as on Lookout Mountain and in 

the areas to the south (Waters, 1955; and Swanson, 

1967) it is clear that the shedding of Ellensburg-like 

silicic volcanic debris eastward from the Cascades was 

not confined to the latter part of the eruption of the 

Yakima Basalt Subgroup, but commenced before the earliest basalt flows reached the area.

SURFICIAL DEPOSITS AND LANDFORMS 

DEPOSITIONAL FACIES

Till, poorly sorted muddy gravel containing 

stones of diverse lithology, forms moraines in the 

valleys and a discontinuous blanket in the uplands of 

westernmost Kittitas Valley. Both the nonglacial mainstream (Yakima River) alluvium and the outwash spread 

downvalley from moraines consist of moderately to 

well-sorted sandy gravel comprising rounded stones of 

diverse volcanic, metamorphic, plutonic, and sedimentary rock types derived mostly upstream of Kittitas 

Valley. Sidestream alluvium graded to the mainstream 

deposits is easily distinguished by its monotonous 

content of subrounded to subangular basaltic gravel. 

The sidestream fans head along the mountain front at 

the mouths of canyons, but on interfluves merge upslope with steep fans of angular basaltic colluvium. 

Sand and silt layers, presumed to be fluvial overbank 

deposits and loess, occur mainly as minor beds within 

and atop mainstream deposits. Fine tephra occurs as 

rare discontinuous beds enclosed by alluvium and colluvium.
LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

120°45'

47° 10'

47°00'

Figure 2. Geologic map of Kittitas Valley area. Base from U.S.
SURFICIAL DEPOSITS AND LANDFORMS

10 KILOMETERS 

I

I

5 MILES

120°30'

Geological Survey Wenatchee quadrangle, Washington, scale 1:100,000.
LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

CORRELATION OF MAP UNITS (figures 2 and 4)

f> Holocene 

Pleistocene

Pliocene 

Miocene 

Eocene

cc

>- 

cc 

<

—-L...

Contact—Precisely to approximately located. 

Dashed where gradational or inferred

Fault—Dashed where approximately located; 

dotted where concealed. Bar and ball on 

downthrown side

Crest of moraine

Overridden moraine or drumlinoid topography

Strike and dip of Yakima Basalt 

Locality referred to in text

Faults referred to in text 

Direction of movement of landslide 

Basement structure from magnetic survey

DESCRIPTION OF MAP UNITS (figures 2 and 4)

Qm Alluvium, mainstream (Yakima River) facies

Qs Alluvium, sidestream facies

Qal Alluvium, undifferentiated

QI Landslide deposit-Arrows indicate direction of movement

Lakedale Drift outwash. Divided into: 

Qlm Mainstream facies 

Qis Sidestream facies 

Qiu Outwash, undifferentiated

Kittitas Drift. Divided into:

Qkit Indian John phase, till

Qkim Indian John phase, mainstream outwash

Qkis Indian John phase, sidestream facies

Qkst Swauk Prairie phase, till with discontinuous loess cap

Qksm Swauk Prairie phase, mainstream outwash

Qkss Swauk Prairie phase, sidestream facies

Qkus Undifferentiated sidestream facies

Qimr Lookout Mountain Ranch Drift

Thorp Gravel. Divided into:

Ttm Mainstream gravel. Locally includes thin discontinuous cap of Tts 

Tts Sidestream gravel

Te Ellensburg Formation; fluvial cobble .gravel, sandstone, and lahars

Ty Yakima Basalt Subgroup. Grande Ronde Basalt of Swanson and others (1977)

Ttr Teanaway Basalt and Roslyn Formation, undifferentiated
SURFICIAL DEPOSITS AND LANDFORMS

Series

UJ

Z

UJ

8

§

<u c 

a a)

Q.

—4

<uc

11

o

§

=5

1

a>

c 

a>

o

§

5

5

o

Group

Q_

0 

6

"5

u>

0)

O

JO

E

1

Subgroup

a.

o

0)

-O

to

"5

o

CQ 

o

E

o

>-

Formation

Saddle

Mountains

Basalt

(10 named members,

separated by disconformities and

tongues of

Ellensburg

Formation)

Wanapum Basalt

(3 named members

in central Washington)

£•

15

I

1

tnCTJ

&

&

m

£

I

o 

a

_ /Vantage Sandstone \ _

Member of Mackin ( 1961 )

Grande Ronde Basalt

(Many flows undifferentiated as members;

many sedimentary

interbeds in Kittitas

Valley area)

K-Ar age 

(m.y.)

6

8.5

10.5

12

14

to

16.5

Stratigraphic range of 

Ellensburg Formation

?

'

1 | '

I o* 1

7 !>

y « -o

1 |2

w .^ u

?!

1

1 ^

1 »

4

Figure 3.--Nomenclature and K-Ar ages of the Yakima

Basalt Subgroup, abridged from Swanson and others 

(1977), and showing Stratigraphic position of 

Vantage Sandstone Member of Mackin (1961) and 

Stratigraphic range of the Ellensburg Formation 

as variously defined.

CRITERIA FOR SUBDIVISION

The Pliocene and Pleistocene sequence in Kittitas 

Valley is subdivided largely on the basis of relative 

geomorphic position. In the western end of the valley 

sets of moraines are separated from sets farther upvalley by moraine-free areas. From each of these moraine sets an outwash terrace grades downvalley, such 

that in central Kittitas Valley the several outwash 

(mainstream) terraces are nested one inside another, 

forming four paired terrace levels. In northern Kittitas Valley four levels of sidestream terraces are 

nested one inside another, each of them graded southward to one of the mainstream (outwash) terraces. 

Relative altitude and longitudinal position of geomorphic features in the valley are thus the foremost criteria for subdividing the surficial deposits of Kittitas Valley. Each of the despositional surfaces that 

connects a moraine to a mainstream terrace, and a 

sidestream terrace to a mainstream terrace, is a geomorphic memento of the conclusion of an episode of 

aggradation in the valley. All of the lithologically 

varied deposits underlying such a surface predate the 

surface; all of the deposits within valleys incised 

below such a surf ace postdate the surface. These isochronous depositional surfaces are used to divide the 

lithologically varied ensemble of surficial deposits 

into local time-stratigraphic units.

Useful to confirm the geomorphic subdivision and 

to temporally group the various bodies of drift are 

time-dependent criteria like soil development (color, 

thickness, horizonation, clay content), degrees of 

weathering of surface and subsurface stones, thickness 

of loess cover, and presence of paleosols (Porter, 

1975, 1976; Coleman, 1976).

There is little field evidence with which to 

evaluate whether any of the terraces are surfaces cut 

in older alluvium, rather than being, as I perceive 

them, nested fill terraces. The mainstream terracegravel units are so lithologically similar that the 

deposits of different ages are distinguished only by 

their relative geomorphic positions and by differences 

in weathering, soil development, and loess thickness 

at their surfaces. Because all of the prominent terraces are traceable upvalley to moraines, it is 

thought that the terraces were formed during aggradational rather than degradational episodes. Most of 

the alluvium underlying a given terrace therefore is 

thought to be related to the same episode of aggradation that formed the surface. With the possible exception of the Thorp Gravel, the deposits of Kittitas 

Valley therefore are thought to represent a series of 

relatively brief episodes of aggradation and swift incision, each followed by a lengthy episode when the 

Yakima River and its tributaries flowed at or near 

their present grades.

NOMENCLATURE

Blackwelder (1915, 1931), dividing alpine-glacial 

sequences in Wyoming and in the eastern Sierra Nevada 

on regionally applied time-stratigraphic bases, named 

the divisions "stages", drawing precedent from that 

crucible of glacial terminology, the Midcontinent. 

"Stage," however, has all but disappeared from the 

glacial literature of the West, having been superseded 

by descriptive lithologic terms like "drift" and 

"till", and by reference of deposits to a "glaciation." The terms "drift" and "till", sometimes regarded as rock-stratigraphic units, in fact refer to 

units that are time-stratigraphic in nature. 

Blackwelder (1915, 1931), for example, again taking 

precedent from the Midcontinent, used "Pinedale drift" 

and "Sherwin till" nearly synonomously with "Pinedale 

stage" and "Sherwin stage," his contexts leaving no 

doubt that he intended each of these terms in a timestratigraphic sense.

The Code of Stratigraphic Nomenclature (American 

Commission on Stratigraphic Nomenclature, 1970) is an 

ambiguous guide for time-stratigraphic classification 

and nomenclature of Quaternary alpine deposits, which 

in practice are divided on a morphologic or time-stratigraphic basis, and only later, if at all, are further divided on a rock-stratigraphic basis. Richmond 

(1962) and Porter (1976) divided glacial deposits into 

"formations" or "drifts", said to be rock-stratigraphic units of formation rank, and divided some of 

these into "members." While the division of a "formation" or "drift" into "members" conforms to Articles 6 

and 7 of the Code, the lithologic character of such 

drifts and the criteria used in their distinction violate Article 5. A single drift, or a named "member"
LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

47° 10'OO'/

47°07'30"

Figure 4. Geologic map of part of northern Kittitas 

Valley, showing topographic and stratigraphic evidence of westernmost of three faults that offset

of a drift, comprises sediment as lithologically varied as boulder till and loess; a drift, unlike a bedrock formation or member, is not distinguished by lithology from neighboring lithologically heterogeneous 

drifts; it is distinguished by its geomorphic position 

and continuity, and perhaps by its geomorphic character; it is independent neither of time concepts nor 

of inferred geologic history. Such drifts and socalled "formations" and "members" in fact are more time 

stratigraphic in nature than rock stratigraphic.

While "formation" and "member" seem to be inappropriate designations for the divisions and subdivisions of glacial deposits in Kittitas Valley, neither 

does it seem correct to use the accepted time-stratithe Thorp Gravel. Base from U.S. Geological Survey Mount Stuart 4 NW quadrangle, Washington, unedited advance sheet, 1959.

graphic terms "stage" and "substage" when the units 

are intended only for local use.

The terminology adopted herein, which is only a 

temporary expedient until an appropriate terminology 

is developed for the region, deviates only a little 

from Porter's (1976) formal names. I retain Porter's 

term "Kittitas Drift" for the larger unit, though explicitly as a local time-stratigraphic term of stage 

rank. Porter's Swauk Prairie and Indian John "Members" are informally designated the Swauk Prairie and 

Indian John phases, both intended as local chronostratigraphic units of substage rank. The Kittitas Drift 

thus comprises the Indian John phase and the Swauk 

Prairie phase.
SURFICIAL DEPOSITS AND LANDFORMS

Unlike Porter, I include within each of the 

drifts and phases substantial volumes of sidestream 

gravel, which, while not strictly glaciogenic, accumulated pari passu with outwash in the main valley. 

Otherwise I deviate from Porter's conception of the 

Kittitas-aged units mostly in name.

CORRELATION OF SURFACES AND DEPOSITS

Table 1 summarizes the Pliocene and Pleistocene 

morpho- and time-stratigraphic sequence in Kittitas 

Valley. Terraces along the southern side of Kittitas 

Valley are distinct and nearly continuous and are 

readily traced upvalley to moraines. A prominent terrace (fig 2, loc I) on the southern side of the Yakima 

River, for example, heads at the moraines of the Swauk 

Prairie Drift that form Thorp Prairie; the next lower 

terrace is a remnant of the prominent surface that 

grades downvalley from the Indian John moraine (loc. 

J). It is by similar geomorphic relations that the 

deposits are divided into the several time-stratigraphic units and are locally correlated in the map area.

The weathered character of many geomorphic surfaces also is distinct. Stones of Grande Ronde Basalt 

and of andesite on the lowest terraces have oxidation 

rinds less than 1 mm thick and are uncemented; volcanic stones on intermediate-level surfaces have oxidation rinds a few millimeters thick but are only 

slightly cemented; on the highest surfaces these 

stones are partly rotten and are deeply cemented with 

hematite and montmorillonite. Porter (1975) noted 

distinct differences of weathering-rind thickness on 

clasts of the Eocene Teanaway Basalt between the 

several geomorphic surfaces; his data have been independently reproduced,by S. M. Coleraan (1976; oral coramun., 1977). High surfaces invariably are more weathered than intermediate surfaces, which in turn are 

more weathered than low surfaces. Relative heights 

and degrees of weathering together thus are the means 

of correlation between the terraces.

Young fans and colluvium that have prograded 

across older surfaces complicate cartography and timestratigraphic designations. Holocene fans overlie 

all terraces; those atop the Kittitas terraces probably accreted throughout the last interglaciation,

last glaciation, and the Holocene Epoch. Despite 

these younger surficial materials, the height of 

the mainstream gravel above the modern stream and the 

weathered character of that gravel generally identify 

a terrace.

ALLUVIUM AND DRIFT 

Thorp Gravel

Definition.--A weakly cemented, deeply weathered 

gravel forming a conspicuous terrace 100 to 220 m 

above the Yakima River in Kittitas Vallpy originally 

was included within the Ellensburg Formation (Smith, 

1904). Porter (1976) inferred that the gravel (sediment) which overlies typical Ellensburg Formation 

(rock) is glacial outwash and named it the Thorp 

Drift. Because of the apparent Pliocene age of the 

gravel, its improbable correlation with drift on Lookout Mountain and in Horse Canyon, and the possibility 

that it is not glaciogenic at all, the accumulation is 

here renamed the Thorp Gravel.

The Thorp Gravel consists mostly of two facies: 

mainstream gravel, most of whose stones are rounded to 

subrounded and comprise durable silicic to intermediate volcanic rocks; and sidestream gravel consisting 

mostly of subangular clasts of Grande Ronde Basalt. 

The type locality of the mainstream facies (fig 2, loc 

A), a landslide scar in the NE% sec. 12, T. 18 N., R. 

15 E., along the northern side of the Yakima River 1.5 

km east of Thorp, Kittitas County, was designated by 

Porter (1976, p. 66) as the type locality for the outwash facies of his Thorp Drift. The base is not exposed at the type locality, but, in small stream valleys 7 km to the northwest, Thorp mainstream gravel 

unconformably overlies the Ellensburg Formation. The 

low-relief upper surface of the Thorp mainstream terrace, which slopes generally about 16 m/km southeastward, roughly parallel to the grade of the modern 

Yakima River, is incised as deeply as 100 m by small 

generally southeast-trending creek valleys whose cross 

profiles are curiously asymmetric, having southwestfacing sides averaging 30° and northeast-facing sides 

about half as steep. Where not affected by these incised valleys, the upper surface apparently is only a

Table 1.--Nomenclature of surficial deposits in upper 

Yakima drainage basin

Upper Yakima valley 

(Porter, 1976)

Kittitas Valley 

(this report)

Holocene deposits

Pleistocene

Lakedale Drift

includes four named 

members 

Kittitas Drift

Indian John Member 

Swauk Prairie Member

Thorp Drift

Till and Outwash

Holocene

Alluvial deposits 

Pleistocene

Lakedale Drift

Kittitas Drift

Indian John phase 

Swauk Prairie phase

Lookout Mountain Ranch Drift

Disconformity 

Pliocene

Thorp Gravel
10 LATE GENOZOIG DEPOSITS, KITTITAS VALLEY, WASHINGTON

little modified, and in a readout 2 km north-northwest (loc. L) of the type locality displays a brown 

(7.5 YR 4/3) to yellowish red (5 YR 4/6) soil having 

a very argillic B horizon as thick as 45 cm within 

which plutonic stones are rotted. There is no evidence that this surface has ever been overlain by 

anything other than incidental veneers of loess and 

fine tephra.

The type locality for the sidestream facies of 

the Thorp Gravel is a small abandoned gravel pit in 

NE%SE% sec. 6, T. 18 N., R. 19 E., Kittitas County, 

Colockum Pass SW 7.5-minute quadrangle (fig 2, loc. 

K). The pit exposes 6 to 8 m of gravel whose clasts, 

angular to subrounded, reach 38 cm in intermediate 

diameter arid are entirely of Grande Ronde Basalt derived from the mountain front 6 km to the north. The 

deposit is thick bedded, comprising beds variously of 

small pebble to cobble gravel enclosed in a sandy 

granule basalt-clast matrix ranging from closely packed to meagerly openwork. Within 1 m of the surface 

the basaltic stones have thick oxidation rinds, vague 

Liesegang banding, and deep cracks. The sidestream 

facies is conspicuously cemented at the type locality 

to a depth of at least 10 m with alternating bands of 

reddish hematite and, verified by x-ray diffraction, 

pale-yellow montmorillonite. Similar material can be 

seen in many localities to the west and south, as at 

localities B, C, E, F (fig. 2). The type locality 

does not reveal the base of the sidestream facies, 

but gullies incised into the western remnant of the 

Thorp sidestream terrace 17 km northwest of the type 

locality reveal that the sidestream facies overlies 

the Ellensburg Formation and the Grande Ronde Basalt 

with an angular unconformity (figs. 2 and 4).

The upper surface of a prominent Thorp sidestream 

terrace 3 km west of the type locality slopes about 22 

m/km to the south-southwest and evidently is a primary 

depositional surface, albeit is dissected like the 

mainstream terrace. A similar Thorp sidestream terrace 14 km farther northwest is smoothly graded to the 

top of the Thorp mainstream terrace. Like the surface 

of the mainstream terrace, there is no evidence that 

the Thorp sidestream terraces have ever been buried by 

anything but a veneer of loess and tephra.

The surface of the western Thorp sidestream terrace contains several percent of rounded to subrounded 

pebbles and granules of various resistates not derived 

from the Grande Ronde Basalt, wherein the headwaters 

of the modern streams that incise in the terrace originate. These resistates include variously colored 

chert and opal; variegated chert-granule conglomerate; 

various porphyritic and nonporphyritic durable felsites; quartzite; vein quartz; fine-grained dense black 

basalt (Teanaway Basalt); and a characteristic opal 

popularly known as "Ellensburg blue," whose bedrock 

source is the Teanaway Basalt. The resistates signify that while the western part of the Thorp sidestream gravel accumulated, the contributing streams 

headed in the Teanaway Basalt and Swauk Formation, 

which crop out north of the updip limit of the Grande 

Ronde Basalt. The beheading of these streams by the 

Swauk Creek tributary, First Creek, (fig. 2, loc. P), 

a capture described by Russell (1900, p. 124) and 

Smith (1904, p. 3), therefore occurred after the accumulation of the Thorp Gravel. The lack of these resistates in sidestream deposits of the Kittitas Drift 

indicates that the capture took place prior to 

Kittitas time.

Stratigraphy and sedimentology.--At the type locality of the mainstream facies (fig. 5) five mixedlithology gravel layers, each 5 to 15 m thick, separate much thinner layers of sand (overbank alluvii— 

z 

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LOCALITY

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THICKNESS, 

METERS IN 

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80-

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LITHOLOGY

Sidestream (basaltic) gravel

^^ Tephra, 3.7±0.64 m.y.

Mainstream (mixed-lithology) gravel

Loess(?)

Mainstream gravel; contains large 

angular silt clasts near base

Paleosol(?) 

Sand and silt

Mainstream gravel

Sand, with paleosol(?)

\ Tephra, 3.6±1.3 m.y.

N^ Sand and silt

Mainstream gravel

Sand and silt

Mainstream (mixed-lithology) gravel

Sandstone, conglomerate, diamictites 

(lahars), siltstone. Paleosol 

near top of section

Figure 5.--Composite section of Thorp Gravel at type 

locality of mainstream facies (fig- 2, loc. A), 

and nearby locality (fig. 2, loc. C) containing 

upper tephra and sidestream facies.
SURFICIAL DEPOSITS AND LANDFORMS 11

urn ?), silt (loess?), and rare tephra. While the 

mean grain size varies within the gravel units, 

there are no consistent differences in grain size, 

sorting, bedding character, or lithology of clasts 

among the gravel units. The fine layers persist for 

100 m or more along the exposure, showing the general conformity of the bedding. Several oxidized 

zones, possible paleosols (fig. 5), are present at 

the type locality, though ground water seepage, which 

occurs at several levels, may account for some of the 

zones. In a roadcut 2 km to the north-northeast (loc. 

L), a brown (10 YR 5/4) argillic paleosol 60 cm thick 

is buried 4 m below the upper surface of the deposit. 

While the paleosols and minor unconformities--gravel, 

for example, channeled a few decimeters deep into underlying sandy mud--indicate minor hiatuses within 

the Thorp Gravel, the several gravel layers are so 

lithologically and sedimentologically similar as to 

appear related and not of greatly different ages.

In several localities (fig. 2, Iocs. B, C, D, and 

E) where the mainstream and sidestream facies occur in 

the same section, the basaltic gravel overlies the 

mixed-lithology gravel, indicating progradation by 

high-gradient sidestreams after the Yakima River abandoned, or migrated to the southwestern margin of, the 

mainstream surface. At locality F along Dry Creek, 

basaltic gravel apparently intertongues with mainstream gravel, indicating that sidestream fans occasionally spread over the mainstream surface during aggradation; at locality G, a layer of mixed composition 

is sandwiched between the dacite-rich basal gravel and 

a basalt-rich surface gravel, indicating that the 

mainstream and sidestream facies occasionally intermixed at their margins.

Paleocurrent indicators and changes in grain size 

and in pebble lithology reflect the direction of 

transport in both facies. Paleocurrents inferred from 

pebble imbrication and from crossbedding vary greatly 

but in the mainstream facies are generally eastward, 

and in the sidestream facies in northern Kittitas Valley are generally southward, indicating paleocurrents 

roughly parallel to the modern incised drainage. The 

intermediate diameter of the largest clast in the 

mainstream gravel near Thorp (fig. 2, loc. A) is 20 

cm, but at Craigs Hill 14 km downvalley (loc. B) is 

9 cm; the nonvolcanic fraction near Thorp is about 25 

percent, of which one-fifth or more is plutonic 

stones, whereas at Craigs Hill the nonvolcanic fraction is less than 2 percent and evidently includes no 

plutonic stones. The maximum size of basaltic stones 

in the sidestream gravel decreases from 50 cm near 

the mountain front to 10 cm where the toe of the sidestream fan overlies the mainstream terrace just north 

of the Yakima River.

Age.--Table 2 shows data on fission-track dates 

(by C. W. Naeser, U.S. Geological Survey) on zircons 

from two tephra layers interbedded with the Thorp 

Gravel (fig. 5). Because the samples bracket the upper half of the thickest section of Thorp Gravel, 

these dates suggest that all of the Thorp is Pliocene 1 . 

Geomagnetically reversed layers within the Thorp Gravel therefore must lie within the Gilbert reversed polarity epoch, rather than within the Matuyama epoch 

as suggested by Porter (1976).

Origin.--Porter (1976) argued that tne rnorp 

Gravel is an outwash facies of a pre-Kittitas drift 

that he named the Thorp Drift. While many characteristics of the Thorp Gravel are consistent with the 

outwash hypothesis, several relations suggest that it 

does not correlate with the till on Lookout Mountain 

and in Horse Canyon. First, the great lithologic variety of till on Lookout Mountain and in Horse Canyon 

contrasts with the overwhelming dominance of intermediate volcanic stones in the Thorp mainstream gravel. Second, the heights of the Thorp and the Swauk 

Prairie terraces are very different, despite the 

proximity of the downvalley limits of Porter's (1976) 

Thorp and Swauk Prairie till. Third, whereas the 

Thorp Gravel is weakly but distinctly cemented, till 

on Lookout Mountain and in Horse Canyon is uncemented. 

Fourth, Thorp sidestream gravel caps the narrow divide east of Horse Canyon and perhaps part of the 

divide west of Horse Canyon, suggesting that it formerly extended over the area now occupied by Horse 

Canyon. Because drift in Horse Canyon postdates the 

excavation of the canyon, the "till facies" of Porter's 

Thorp Drift evidently postdates his "outwash facies".

A preliminary K-Ar age by R. W. Tabor and W. C. Gaum 

(written commun., 1978) on hornblende crystals from 

a tephra layer in SW%NE% sec. 35, T. 18 N., R. 17 E. 

and of stratigraphic position intermediate between 

the two tephra layers yielding the fission-track 

dates, is 4.40±8;^§ m.y. The statistical error overlaps the mean of'each of the two fission-track dates.

Table 2. --Fission track ages by C. W. Naeser on zircon

from two layers of tephra in Thorp Gravel (C. W.

Naeser, written commun, 10/20/76). Discussion of

techniques in Naeser (1969) and Izett and Naeser

1976)

Spontaneous tracks

Collector, 

Field No. , Crystals 

Lab. No. counted

S. C. Porter, 

5 Porter U. Wa. , 4 

DF-743

R. B. Waitt, 

RBW 75.410, 6 

DF-1047

Uranium 

concen. 

(ppm)

28Q 

320

No. 

counted

32 

147

Density1

0.553 

0.635

Induced

No. 

counted

482 

1280

tracks

Density 1

16.6 

11,1

Neutron Age 3 

flux2 (m.y. ±2a)

1.79 3.64 ± 0.74 

1.05 3.70 ± 0.2

x Values x 10 6 /cm2

2Values x 10 15 neutrons/cm2

A = 6.85 x 10" 17 yr" 1
12 LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

With the possible exception of the apparent antiquity of the Thorp, its characteristics generally 

are consistent with an origin as outwash. A striated 

boulder found on the Thorp mainstream surface 2 km 

from the head of that surface certainly keeps this 

possibility open. If it is outwash, however, it must 

substantially postdate the Lookout Mountain Ranch 

Drift.

An alternative origin of the Thorp Gravel is aggradation caused by local tectonic activity. Mainstream aggradation can occur as well by interruption 

of grade downvalley as by increased load (because of 

glaciers) upvalley. Because the Yakima River is antecedent to the anticlines south of Ellensburg (Smith, 

1903), aggradation in Kittitas Valley should have resulted whenever the rate of relative uplift of the 

anticlines exceeded the rate of stream incision. The 

structure-transverse segment of the Yakima River south 

of Ellensburg coincides with a cross-structural sag, 

toward which prominent east-trending anticlines and 

intervening synclines plunge eastward from the Cascade 

Range and westward from the Hog Ranch axis (fig. 1). 

The coincidence of the Yakima River with a structural 

sag is either fortuitous or admits that during relative uplift of the ridges, the Yakima River was defeated from an earlier course into its present structurally and topographically favorable course. Such a 

tectonic diversion should have caused aggradation upstream: an ancient, tectonically caused aggradation 

in Kittitas Valley is thus deductively logical. 

Whether the Thorp Gravel represents this aggradation, 

or instead represents relative upward movement on the 

anticlines south of Kittitas Valley after the Yakima 

River acquired is present course, is an open question. 

That the Thorp apparently is not involved in the regional folding would suggest the latter, as is inferred (Newcomb, 1958; Brown and McConiga, 1960; 

Newcomb and others, 1972) for the Pliocene Ringold 

Formation, which is stratigraphically to Pasco Basin 

what the Thorp is to Kittitas Valley.

Correlation.--The only known deposit in the region 

with which the Thorp Gravel may be reasonably correlate is the Ringold Formation, which crops out typically on the White Bluffs of the Columbia River in the 

central part of the Pasco Basin, 120 km southeast of 

Kittitas Valley (fig. 1). After comprehensive reexaminations of Ringold vertebrate faunas, Gustafson 

(1973, 1976, 1977, 1978) and Tedford and Gustafson 

(1977) designated the fauna from the gravel member as 

Hemphillian; they inferred that the fauna from below and 

above a prominent tuff higher in the Ringold is very 

early Blancan.

According to the time scale of Berggren and 

van Couvering (1974, fig. 11), the Hemphillian-Blancan 

boundary is at about 3,9 m,y.; and according to comparison by Tedford and Gustafson of the Taunton and 

White Bluffs Local Faunas with the Hagerman Local 

Fauna of Idaho, the upper unit of the Ringold is no 

younger than 3.2 m.y. old. From recent northern hemisphere geochronologic, biochronologic, and geomagnetic data, C. A. Repenning (oral commun., 1978) and 

Repenning and Fejfar (1977) suggest an approximate 

age of 4.5 m.y, for the very early Blancan. The 3.7 

m.y. Thorp Gravel either correlates with the upper 

part of the Ringold containing the very early Blancan 

fauna, or is as much as one million years younger.

Lookout Mountain Ranch Drift

Definition and description.--Till preserved on 

Lookout Mountain 70 m or more above the well-defined 

Kittitas (Swauk Prairie) moraines is here designated 

Lookout Mountain Ranch Drift, named for the ranch that 

occupies most of the top of Lookout Mountain. The 

type locality is the exposure at the top of the northwestern scarp of Lookout Mountain, at altitude 1,000 

to 1,300 m, in SE%SW% sec. 36, T. 20 N., R. 16 E., Cle 

Elum is-minute quadrangle, Kittitas County, where the 

drift unconformably overlies the Grande Ronde Basalt 

(fig. 2). One to 3 km beyond the well-defined type 

Swauk Prairie moraine the drift is also exposed in 

.Horse Canyon, the type locality of the till facies of 

Porter's (1976, table 4) Thorp Drift.

The Lookout Mountain Ranch Drift consists of a 

varied lithologic mix including porous dark-gray basalt (Grande Ronde Basalt), fine-grained dense black 

basalt and diabase with brown rind (Teanaway Basalt), 

several varieties of felsite and dikerock porphyry, 

altered porphyritic andesite (Keechelus Andesitic 

Series of former usage) t granodiorite, gneiss, quartzite, gray to black chert-pebble conglomerate (Guye 

Formation), sandstone and siltstone (Swauk and Rosylin 

Formation), vein quartz, chert, and opal. As described by Porter (1976), the till forms subdued lateral 

moraines on the southern slope of Lookout Mountain and 

on the western side of Horse Canyon. Most rock types 

are conspicuously weathered, and the till at the type 

locality has a soil that includes a reddish brown (5 

YR 4/4) argillic B horizon at least 50 m thick; but it 

also locally displays a few surficial clasts of partly 

weathered granodiorite and contains conspicuously 

striated cobbles of hornfels and volcanic rocks. The 

Lookout Mountain Ranch Drift evidently is less weathered than the Thorp Gravel and is uncemented.

Unlike the younger drift sheets in the upper 

Yakima Valley, the Lookout Mountain Ranch Drift has no 

recognized outwash facies. The reason for the absence 

of outwash is unclear, but the pattern is not unlike 

that 45 km to the north in the Wenatchee Valley. 

Page's (1939) Peshastin Till and Leavenworth Till, 

which evidently correlate respectively with the 

Kittitas and Lakedale Drifts in Yakima Valley, include 

easily recognized outwash terraces immediately downvalley of the valley-floor moraines. An older drift, 

conspicuously weathered and forming an eroded lateral 

moraine well above the outer Peshastin moraine on 

Boundary Butte, does not include a recognizable valley 

train in the Wenatchee Valley (Waitt, 1977).

Age and comparison to Thorp Gravel.--As compared 

to the outer Kittitas moraine on Lookout Mountain, the 

Lookout Mountain Ranch moraines are at higher altitudes, are broader and flatter, have a redder surficial hue, and display fewer surficial boulders. The 

Lookout Mountain Ranch Drift thus is distinctly older 

than the Swauk Prairie Drift. Several lines of evidence suggest, however, that it is not millions of 

years older. The Lookout Mountain Ranch Drift has 

been exposed to weathering since its deposition, but 

nonetheless displays a variety of slightly to moderately weathered stones, including a few coarse-grained plutonic and metamorphic rocks. Although the soil 

on the Lookout Mountain Ranch Drift is well developed, it does not resemble the deep cementation of the
SURFICIAL DEPOSITS AND LANDFORMS 13

Thorp Gravel. Moreover, whereas the Thorp Gravel is 

extensively dissected by triburary canyons as deep as 

100 m, the original shape of the moraines on Lookout 

Mountain and in Horse Canyon is still recognizable. 

These criteria together with geomorphic evidence that 

Horse Canyon postdates the Thorp Gravel indicate that 

the Lookout Mountain Ranch Drift is much younger than 

the Thorp Gravel, though definitely older than the 

Swauk Prairie Drift.

Kittitas Drift

The Kittitas Drift, deposited during the penultimate glaciation of Yakima Valley, comprises the Swauk 

Prairie phase (older) and the Indian John phase. 

Massive moraines at Swauk and Thorp Prairies define 

the downvalley limit of glaciers that deposited the 

Swauk Prairie phase. A well-defined mainstream terrace (fig. 2, loc. I) 60 to 100 m above the modern 

river descends downvalley from the moraines at Thorp 

Prairie; a lower, equally prominent terrace 30 to 60 m 

above the river descends from the Indian John moraine 

(loc. J) (Indian John phase) farther upvalley. Stratigraphic exposures at Thorp Prairie, Swauk Prairie, 

and Indian John Hill show that while each of the moraines consists of till, the till is a veneer variously 0 to 10 m thick overlying mainstream gravel, evidently recording the advance of glacier ice over its 

own proglacial outwash. The Indian John and Swauk 

Prairie phases show similar degrees of weathering and 

soil development, suggesting that both accumulated 

during a single glaciation (Porter, 1975, 1976; 

Coleman, 1977); hence their grouping under the common 

name Kittitas Drift.

Several remnants of sidestream terraces in northern Kittitas Valley are roughly graded to the Kittitas 

mainstream terraces and have weathering characteristics intermediate between those of the Thorp surface 

and low-level surfaces. Like Thorp sidestream terraces, Kittitas terraces that descend from the northern 

mountain front consist of basaltic gravel. A well-defined surface that heads 2 km south of Green Canyon 

and continues 15 km southward unambiguously matches 

the Indian John mainstream terrace south of the Yakima 

River (fig. 2). I therefore correlate sidestream terraces in northern Kittitas Valley that are above the 

Indian John sidestream surface, but well below the 

Thorp sidestream surface, with the Swauk Prairie mainstream terrace.

Soil on the Kittitas Drift in many places is well 

developed. On the outer moraine of the Swauk Prairie 

phase on Lookout Mountain the soil displays a brown 

(7.5 YR 4/4) textural B horizon at least 60 cm thick, 

which probably developed during the last major interglaciation. This soil resembles the buried paleosol 

developed on Kittitas-aged loess and the underlying 

till of the Swauk Prairie phase at Swauk Prairie 

(Porter, 1976, Fig. 9. loc. 12). Kittitas Drift 

therefore apparently represents the penultimate full 

glaciation of the marine isotope record, of which 

Stage VI culminated 0.14 to 0.13 m.y. ago (Emiliani 

and Shackleton, 1974, Time Scale D; Hays and others, 

1976). Remarkably similar ages are reported in two 

continental glacial sequences: Pierce, Obradovich, 

and Friedman (1976) obtained an age of about 0.14 m.y. 

for the Bull Lake Drift in West Yellowstone, Mont.,

and Porter, Stuiver, and Yang (1977) reported an age 

f 0.130 to 0.136 m.y. for the penultimate glaciation 

of Mauna Kea, Hawaii.

At Craigs Hill in the town of Ellensburg, the 

downsection change from normal to reversed polarity 

(the Brunhes-Matuyama boundary, 0.7 m.y. ago) occurs 

below the well-developed post-Kittitas soil 

(S. C. Porter, written commun., 1975). The available 

paleomagnetic and soil data therefore are internally 

consistent in the Kittitas Drift.

Lakedale Drift

Outwash of the Lakedale Drift, forming three or 

more terraces near Cle Elum (Porter, 1976), forms a 

single well-defined mainstream terrace 5 to 10 m above 

the Yakima River in Kittitas Valley. The terrace is 

nearly continuous along the southern bank of the river 

but is dissected by several tributaries on the northern side. Partly of Holocene alluvium, the floor of 

Green Canyon Creek also forms a terrace above the floor 

of Dry Creek distinctly below the Indian John sidestream terrace; it is therefore correlated with the 

Lakedale mainstream terrace (fig. 4).

Weathering rinds on fine-grained stones in the 

Lakedale Drift are less than 0.7 mm thick. Soils, the 

base of whose C horizon is only a meter or so deep, lack 

a textural B horizon and are no redder than 10 YR. The 

freshness of depositional landforms and the meagerness 

of weathering and of soil development identify the 

Lakedale Drift with the Fraser Glaciation of the Puget 

Lowland (see Armstrong and others, 1965) and with the 

late Wisconsin Glaciation of the mid-continent.

Holocene Alluvium

Because Holocene colluvial aprons, tributary fans, 

and sidestream gravel are graded to and cap all preHolocene terraces, they compose the largest area of 

surficial deposits--more area, in fact, than shown in 

figure 2. Near the Yakima River Holocene sidestream 

gravel is smoothly graded to the modern river channel 

and forms surfaces below the Lakedale terrace.

COMPARISON TO GLACIAL SEQUENCE AND 

CHRONOLOGY OF SIERRA NEVADA

A brief comparison of the glacial sequence in 

Kittitas Valley with the dated glacial sequence of the 

eastern Sierra Nevada, a region of broadly similar 

climate, is revealing of relative ages of the older 

surficial deposits in Kittitas Valley. Recent reinterpretation of the Sierra Nevada sequence, moreover, renders the disparity between the glacial sequences in the 

two regions not so great as it formerly seemed.

From new relative-age criteria on the Sierra 

Nevadan drifts and from new limiting dates by Bailey, 

Dalrymple, and Lanphere (1976) on the Casa Diablo Till 

of Curry (1971), Birkeland, Burke, and Yount (1976) and 

Burke and Birkeland (1976) tentatively conclude that 

the Mono Basin and Casa Diablo Tills are temporally related to the Tahoe Drift, and the Tenaya Drift variously to the Tioga and Tahoe Drifts. Personal 

observations on several relative-age criteria, however,
14 LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

convince me to agree with Sharp and Birman (1963) that 

the type Mono Basin moraines are distinctly older than 

the topographically unconformable Tahoe moraines. If 

most of the conclusions of Birkeland, Burke, and Yount 

are correct, however, the eastern Sierra Nevada sequence is not dissimilar to Blackwelder's (1931), as 

is shown on table 3 with suggested correlations to the 

Yakima Valley sequence. The prominent pre-Tahoe drifts 

in the Sierra Nevada are the valley-floor Sherwin Drift 

and the divide-capping McGee Till. Sharp (1968) inferred the age of 0.75 m.y. for the Sherwin Drift, 

which underlies the 0.7 m.y. Bishop Tuff (Dalrymple 

and others, 1965; Izett and Naeser, 1976). The highly 

weathered state of the McGee Till, and the major topographic inversion between the times of deposition of 

the divide-capping and valley-occupying drifts evince 

a large hiatus separating the McGee and Sherwin Drifts 

(Blackwelder, 1931).

In Kittitas Valley the type Lookout Mountain Ranch 

moraines are higher than but parallel to the outer 

Kittitas moraine. Because valleys surrounding the mountain harbor both drifts, the configuration of ridges 

and valleys has not changed greatly since emplacement 

of the drifts. In weathering, preservation of original morphology, and topographic locale the Lookout 

Mountain Ranch Drift far more closely resembles Sherwin 

Drift than it does McGee Drift, despite that weathering 

and erosion of the type Sherwin was retarded by the 

accidental carapace of Bishop Tuff. The Lookout Mountain Ranch Drift probably is no older than Sherwin 

Drift, thus reinforcing the inference that the Lookout Mountain Ranch Drift is much younger than the 3.7 

m.y. Thorp Gravel in Kittitas Valley.

STRUCTURE

FOLDS

The erosionally stripped, centripetally dipping 

surfaces of the Grande Ronde Basalt advertise the snyclinal basin of Kittitas Valley. From a zone of steep 

(10° to 50°) dip along the margins of the basin, the 

basalt strata flatten near the crests of anticlines 

that form the Wenatchee Mountains and Manastash Ridge.

Table 5.--Suggested correlation of surficial deposits 

in Kittitas valley, Washington and in the eastern 

Sierra Nevada, California

Kittitas Valley, 

Cascade Range

(This report)

Approx. age 

(m.y.)

Eastern Sierra Nevada

(Blackwelder, 1931; Sharp and 

Birman, 1963; 

Birkeland and others, 1976)

Unit

0.01-0.02Lakedale Drift 

0.13-0.14 (?) Kittitas Drift

Lookout Mountain 

Ranch Drift

Approx. age 

(m.y.)

Unit

3.7 Thorp Gravel

Tioga Drift 

Tahoe Drift 

Mono Basin Drift 

0.71 Bishop Tuff

Sherwin Drift

McGee Till 

2.7 Basalt

Close to the axis of the basin, strata of the conformably overlying Ellensburg Formation generally dip less 

than 5°. Steeply dipping inliers of basalt trending 

subparallel to the margins of the basin, however, hint 

that minor anticlines or fault blocks lie beneath the 

basin sediments.

West of Ellensburg the Yakima River flows down 

the plunge of the Kittitas Valley syncline; and its 

tributaries, heading on the limbs of the syncline, 

flow generally downdip. Inclined as the underlying 

structure, the depositional slopes of the Thorp mainstream and sidestream terraces are difficult to distinguish from any effects of post-depositional warping. The slope of the Thorp sidestream terrace 

adjacent to lower Green Canyon is, in fact, almost 

identical to the slope of the Lakedale-Holocene valley-floor surface, suggesting that there has been 

little if any post-Thorp basinward tilting.

The gradual upsection decrease in the centripetal dips in the Ringold Formation in Pasco Basin 

suggested to Brown and McConiga (1960) that the deformation of the area including Horse Heaven anticline could have continued at least until the 

conclusion of Ringold deposition. The presence of 

thick strata of clay and silt in the lower and upper part of the Ringold Formation (Newcomb, 1958; 

Brown and McConiga, 1960; Newcomb, Strand, and Frank, 

1972) indicates growth of the Horse Heaven anticline 

at Wallula Gap at least as recently as middle 

Pliocene, the maximum age of the upper Ringold 

according to Gustafson's (1973, 1976) vertebrate

data.

Growth of anticlines south of Kittitas Valley 

may have influenced the accumulation of the Thorp 

Gravel in the Kittitas Valley at roughly the same 

time as the accumulation of the Ringold Formation. 

Most of the early workers, preoccupied with the notion that the courses of the Columbia and Yakima 

Rivers were established prior to the rise of anticlines across their courses, inferred or implied 

that the folds were youthful (Russell, 1900; Smith, 

1903a, b; Willis, 1903; Calkins, 1905). Deformation of early Pleistocene pediments (Waters, 1955) 

and possibly of 19th century flumes (!) (Gilluly 

and others, 1968, p. 131; Brown, 1968, p. 40; 

A. C. Waters, written commun., 1976) suggest that 

some anticlines near Yakima may be still developing. A bulge in the reconstructed profile of Moses 

Coulee suggested to Hanson (1970) Holocene arching 

of the Badger Mountain anticline. The near-faithful 

correspondence of the Columbia and Yakima Rivers to 

structural lows in central and southern Washington, 

together with Schmincke's (1967a) stratigraphy indicating that in the Yakima area the accumulation of 

gravel of Columbia River provenance outlived the accumulation of silicic volcaniclastic sediment, suggest that it was not eastward-accreting fans but 

rising anticlines that defeated the Columbia and lower Yakima Rivers into downwarping basins during the 

Pliocene Epoch (Waitt, 1978). Focal mechanisms of 

earthquakes indicate modern north-south compressive 

stress in Pasco Basin and across the Saddle Mountains 

anticline (Malone, Rothe, and Smith, 1975; 

A. M. Pitt, oral commun., 1976, 1977; Malone, 1978). 

Several pieces of evidence thus suggest that some 

structures in central Washington have grown during 

the Pliocene and younger epochs.
STRUCTURE 15

FAULTS 

Post-Yakima Faults in Central Washington

Faults cutting the Grande Ronde Basalt and Ellensburg Formation associate with many of the anticlines in 

central Washington (Mackin, 1955; Waters 1955; 

Rosenmeier, 1968; Diery and McKee, 1969; Bingham and 

others, 1970; FUGRO, 1974, App. 2B and 2C; Bentley, 

1977). If some of the folds are growing, some of the 

faults may be at least intermittently active. There is 

little evidence, however, that Pleistocene sediment in 

central Washington is either folded or faulted. Brown 

(1968) and Bingham, Loudquist, and Baltz (1970), for 

example, reported no positive evidence of Pleistocene 

faulting in the Hanford area or near Wallula Gap. 

Bingham, Londquist, and Baltz, however, cite evidence 

that the reverse fault north of Saddle Mountains offsets the Ringold, from which Tedford and Gustafson 

(1977) described a vertebrate fauna that closely resembles the early Blancan fauna at White Bluffs.

Faults along lower Coleman and Schnebly Canyons 

(fig. 2, Iocs. M and N) bound a horst made apparent by 

a basinward offset in the mountain front between those 

canyons. Like faults that disrupt the Grande Ronde 

Basalt elsewhere in the region, those peripheral to 

Kittitas Valley evidently do not disrupt modern sidestream fans and thus can be dated only as post-Miocene, 

pre-late Holocene.

Young Faults in Kittitas Valley

Three east-trending north-facing scarps break the 

smooth slopes of Thorp sidestream terraces that descend 

from the northern mountain front. Of two prominent 

remnants of Thorp sidestream terraces, the eastern one 

is interrupted 9 km north of Ellensburg by a conspicuous east-trending north-facing scarp 50 m high, whose 

only reasonable explanation is a fault scarp (fig. 2, 

fault Y). The alined upstream ends of 12 flat-topped 

knolls of Thorp Gravel east and west of the prominent 

Thorp terrace suggest that the fault is at least 10 km 

long. Four magnetic traverses by Weston Geophysical 

Research (1977, fig. 2R 1-34) show an abrupt southward 

rise of about 500 gammas across an east-trending bedrock structure about 500 m south of fault Y (fig. 2). 

Weston 1 s gravity profile (fig. 2R 1-36) shows a conspicuous abrupt rise of about 4 milligals southward 

across the same structure. These geophysical data, 

probably showing the greater depth to the Grande Ronde 

Basalt north of the structure than to the south, indicate that fault Y dips to the south and is therefore a 

reverse fault.

Tributary valleys incised in the western remnant 

of Thorp sidestream terrace reveal an upward stratigraphic succession of the Grande Ronde Basalt, conglomerate and sandstone of the Ellensburg Formation, 

mainstream facies of the Thorp Gravel, and sidestream 

facies of the Thorp Gravel (fig. 4). The unconformity separating the Grande Ronde and Ellensburg from the 

Thorp passes gradually southward beneath the floor of 

the canyons, but abruptly reappears in the walls of the 

canyons approximately where the surface of the terrace 

is interrupted by an east-trending north-facing scarp 

10 to 15 m high. The topography of the surface of the 

terrace and the stratigraphy in the walls of the incised valleys independently denote an east-trending fault 

upthrown at least 30 m to the south (fig. 2, fault X).

The alined northern ends of 15 knolls of Thorp 

sidestream gravel suggest up-to-the-south movement on 

a third fault (fig. 2, fault z) striking eastward for 

11 km from the northern outskirts of Ellensburg. The 

knolls also merge eastward with a northwest-trending 

anticline in the Yakima Basalt Subgroup, but the 

linearity of the dissected scarp and its similar trend 

and appearance to scarps that manifest faults X and Y 

suggest the concealed fault Z dotted on figure 2.

The youngest deposit definitely faulted in 

Kittitas Valley is the Thorp Gravel, whose enclosed 

tephra layers are dated at about 3.7 m.y. old. Sidestream sediments of Kittitas age (presumed to be 0.14 

to 0.13 m.y. old) and of-Lakedale age (20,000 to 10,000 

years old) are not demonstrably offset. The Thorp 

Gravel in Kittitas Valley evidently was faulted between 

3.7 and 0.13 m.y. ago. It is possible, however, that 

younger sediments were faulted and the scarps obscured. 

Were faulting continuous since 3.7 m.y. ago, a 50-m 

scarp across the Thorp Gravel should be less than 2 m 

high across Kittitas surfaces and about 20 cm high on 

Lakedale surfaces. Such small scarps could have been 

obscured by erosion and deposition prior to incision of 

the faulted surfaces.

REGIONAL TECTONIC SIGNIFICANCE

Most folds in central Washington trend eastward; 

those within a 10- to 40-km-wide southeast-trending 

zone that includes the Olympic-Wallowa lineament of 

Raisz (1945), trend southeast. That prominent anticlines like Saddle Mountains, Umtanum and Rattlesnake 

Ridges, and Horse Heaven Hills are kinked abruptly into 

the trend of the linear zone suggests that whatever 

caused the east-west structures outside the zone of the 

lineament also influenced the trends of the same structures within the zone. Wise (1963) inferred an interregional southeast-trending right-lateral wrench system 

that generated not only regional southeast-trending 

right-lateral strike-slip faults but also the easttrending compressional folds. Focal mechanisms of 

earthquakes confirm modern north-south compression in 

the Saddle Mountains-Pasco Basin area (Malone, Rothe, 

and Smith, 1975; A. M. Pitt, oral commun., 1977; 

Malone, 1978). The northern limbs of many anticlines 

in central Washington are disrupted by high-angle, upto-the-south reverse faults (Mackin, 1955; Bingham, 

Londquist, and Baltz, 1970; FUGRO, 1974, App. 2B and 

2C; R. D. Bentley, 1977, and oral commun., 1976 and 

1977); some of the anticlines and faults are arranged 

in southeast-trending dextral echelon systems (fig, 1).

The three east-trending faults in Kittitas Valley 

form an echelon system that trends southeast and is 

antithetic to the basinward dip of the Grande Ronde 

Basalt at the northern margin of the valley. The parallelism of the faults to each other and to anticlines 

farther east, and the similarity of their dextral echelon arrangement to that of the anticlines and their 

attendant reverse faults farther southeast (fig. 1; 

Waitt, 1978), suggest a genetic relation to regional 

structures. An hypothesis consistent with regional 

relations is that the individual east-trending scarps 

in Kittitas Valley evince reverse faults caused by 

north-south compression, and that the southeast trend
16 LATE CENOZOIC DEPOSITS, KITTITAS VALLEY, WASHINGTON

of the dextral echelon pattern is due to a right-lateral couple across a southeast-trending structural zone 

that includes, but is not limited to, the topographically defined Olympic-Wallowa lineament of Raisz (1945) 

about 10 km to the southwest.

Along the segment of the Olympic-Wallowa lineament 

bordering Pasco Basin, the east-northeast-trending 

Rattlesnake Ridge anticline is abruptly kinked into the 

southeast trend of the lineament. Unlike the continuous long Rattlesnake Ridge, however, the southeastern 

extension is a series of short ridges formed by elongate quaquaversal anticlines in the Saddle Mountains 

Basalt (Newcomb, 1970; K. R. Fecht, oral commun., 

1977). Many of the anticlines trend individually about 

azimuth 100 and are collectively arranged dextrally en 

echelon along a 120 azimuthal trend. The echelon arrangement, which has counterparts elsewhere on the 

globe (Harding, 1973; Wilcox, Harding, and Seely, 

1973), requires a right-lateral couple across a roughly 

southeast trend, and the eastward trend of the individual anticlines evinces an associated north-south compression.

That two separated areas near or along the 

Olympic-Wallowa lineament independently indicate similar stress fields suggests that a north-south compressional stress has existed in central Washington, 

and that a right-lateral couple has existed across a 

substantial length of the Olympic-Wallowa structural 

zone, from at least the late Miocene to the middle 

Pliocene.

ACKNOWLEDGMENT

This paper has especially benefited by stimulating 

discussions between 1975 and 1978 with R. D, Bentley, 

R. W. Kopf, S. C. Porter, and D. A, Swanson, who of 

course do not necessarily agree with all of the conclutions herein.

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