y

The Yakima Basalt and 

Ellensburg Formation of 

South-Central Washington

By JAMES W. BINGHAM and MAURICE J. GROLIER

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1224-G

Prepared in cooperation with the 

Washington Department of Conservation 

Division of Water Resources
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

,-c. 

GEOLOGICAL SURVEY _/,

William T. Pecora, Director ^

V

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1966

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

Washington, D.C. 20402 - Price 10 cents
CONTENTS

Page

Abstract_______________________________________________________ Gl

Introduction._____________________________________________________ 1

Columbia River Group___.______--_-__-..__--__--____-___-_---_____ 2

Yakima Basalt._______________________________________________ 2

Vantage Sandstone Member.._-..--____---___-_________--._ 6

Frenchman Springs Member________________________________ 6

Basalt flows-..._______----------___________ 6

Squaw Creek Diatomite Bed---_--_-----__-__---------_. 8

Roza Member__-_-_---__________------__--_------------- 8

Priest Rapids Member_______._____________________________ 9

Quincy Diatomite Bed...______________________________ 10

Basalt nows-_-_-____--__---_-___--------_-----_-_-_-_- 10

Saddle Mountains Member.______________________________ 11

Ellensburg Formation._____________________________________________ 12

Beverly Member__-__-_-___----_____----___-_____________-____ 13

References cited------_---___-_-----___-_---_-----_----___-___---_- 14

ILLUSTRATIONS

j, _____

Page

x FIGURE 1. Diagram showing stratigraphic sequence in the northwestern

._/ Columbia Plateau......_______________________________ G3

2-4. Maps showing: 4

2. Areal extent of the Columbia River Group___--______

3. Towns, and physiographic features--_-_______-______ 5

4. Type sections____________________________________ 7

m
r *~ 

i X
CONTRIBUTIONS TO STRATIGRAPHY

THE YARIMA BASALT AND ELLENSBURG FORMATION OF 

SOUTH-CENTRAL WASHINGTON

BY JAMES W. BINGHAM and MAURICE J. GROLIER

ABSTRACT

The uppermost part of the Yakima Basalt herein assigned to the Columbia 

River Group has the following largely conformable units (from oldest to 

youngest) : lower basalt flows; the Vantage Sandstone Member; the Frenchman Springs Member, which locally includes the Squaw Creek Diatomite Bed; 

the Roza Member; the Priest Rapids Member, which locally includes the Quincy 

Diatomite Bed; and the Saddle Mountains Member. Sedimentary deposits of 

the Ellensburg Formation interflnger with basalt flows of the youngest member 

of the Yakima Basalt.

The maximum thickness of the Yakima Basalt is not known, but the formation is about 4,500 feet thick at a test well drilled in the Odessa area, and is 

probably much thicker toward the center of the Columbia Plateau. The part 

described herein has a composite thickness of about 1,200 feet above the Vantage 

Sandstone Member. The overlying and interflngering Ellensburg Formation is 

as thick as 2,000 feet in the type area, and the Beverly Member, which represents 

the lower part of the Ellensburg in the Sentinel Gap area, is as thick as 300 feet.

The Yakima Basalt is late Miocene and early Pliocene in age, as determined 

from the flora and fauna in the underlying Mascall Formation in Oregon, the 

intrabedded sedimentary rocks and the interbedded and overlying Ellensburg 

Formation.

INTRODUCTION

The stratigraphy of a thick series of outwardly monotonous basalt 

flows in the Columbia Plateau has been studied in the past to determine 

the geologic structure as it affects engineering and ground-water projects. Whether the project is an areal ground-water study or a relatively localized engineering investigation, the presence or absence of 

anticlines, synclines, faults, unconformities, interbedded sedimentary 

deposits, and other features must be known before sound geologic 

interpretations can be made. U.S. Bureau of Reclamation geologists 

and consultants noted about 1940 that some basalt flows in the Columbia Basin Irrigation Project area had distinctive characteristics which

01
G2 CONTRIBUTIONS TO STRATIGRAPHY

enabled them to be mapped. Grolier and Foxworthy (1961) mapped 

two basalt units in the Moses Lake North quadrangle. The names for 

units in the upper 1,200 feet of the Yakima Basalt and the overlying 

and interbedded Ellensburg Formation are herein briefly described hi 

an effort to summarize =the stratigraphic nomenclature. A resume 

of the nomenclature used in this paper is given in figure 1.

.,;_-.. : : .. COLUMBIA RIVER GROUP

Only the upper formation of the Columbia River Group, the 

Yakima Basalt, is exposed in south-central Washington (fig. 2). In 

northeastern Oregon the group also includes older rocks assigned to 

the Picture Gorge Basalt by Waters (1961, p. 607). '

YAKIMA BASALT

The Yakima Basalt was named and defined by Smith (1901, 

p. 15) ,to describe "the great series of [flood] lavas * * * which 

covered the vast area between what is now. the crest of the Cascade 

Mountains on the west and the mountains of Idaho on the east, and 

between the mountains of northeastern Washington on the north and 

the Blue Mountains of Oregon on the south." Smith restricted the 

name to that part of Russell's Columbia Lava (1893, p. 21; 1897, p. 40) 

which is of Miocene age. The name Yakima Basalt has been subsequently used by Calkins (1905), Waring (1913), and Schwennesen 

and Meinzer (1918), and many others.

In 1961, Waters (p. 607) considered the Yakima Basalt to be the 

upper formation of the Columbia River Group. He also confirmed 

(p. 606) the validity of Smith's definition of the formation but extended the time of eruption of the Yakima Basalt flows to early 

Pliocene (p. 608), an age indicated by flora and fauna preserved in 

continental sedimentary deposits of the Ellensburg Formation and in 

beds which interfinger with or overlie Yakima flows near the margin 

of the Plateau. The age of the Yakima Basalt is late Miocene and 

early Pliocene (Fiske and others, 1963, p. 63).

The Yakima Basalt includes individual lava flows, many of which 

are of great lateral extent. The general appearance is monotonous, 

but several flows have characteristics that make them distinctive. 

Among these characteristics are chemical composition; mineralogy; 

color; texture; degree of crystallization; hardness; porosity; number, 

shape, and size of vesicules; thickness; breakage habits; type and spacing of joints; alteration; permeability; and the presence of spiracles 

and pillow zones. Taken separately, no single feature permits the 

lateral tracing of individual flows, but the consistent association of 

several of the characteristics in one flow, when considered in relation
YAKIMA BASALT, ELLENSBURQ FORMATION, WASHINGTON G3

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G4 CONTRIBUTIONS TO .STRATIGRAPHY

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FIGURE 2. Areal extent (stippled) of the Columbia River Group in the northern 

part of the Columbia Plateau. (After Waters, 1961.)

to those of the overlying and underlying flows, is sufficient for stratigraphic identification of some flows over many tens of miles.

The maximum thickness of the Yakima Basalt is not known because the base of the formation is exposed only in scattered outcrops 

near the margin of the Columbia Plateau. About 40 miles from the 

margin of the plateau, in the Odessa area, however, an oil test well 

has penetrated 4,465 feet of basalt, 202 feet of sand and shale, and 

15 feet of granite. Smith (1901, p. 15-16) stated that "more than 

2,500 feet [of basalt] is exposed in vertical section in the canyon of 

the Yakima River, and as the section [there] includes neither the top 

nor the base of the lava series, the real thickness may possibly approximate that along Snake River * * * Canyon, where 3,000 feet of lava 

is exposed * * *."

The exposures of Yakima Basalt in the Yakima River canyon between Ellensburg and Selah (fig. 3) are generally considered typical, 

and that area has been designated the type area (Mackin, 1961, p. 4, 

from Smith, 1901, p. 15) even though the complete sequence of flows 

is not present. Only the upper ] ,200 feet of the Yakima Basalt has
YAKIMA BASALT, ELLENSBURG FORMATION, WASHINGTON G5

121° 120° 119° 118° 117°

40 40 MILES

FIGURE 3. Location of towns and physiographic features.

been extensively mapped and formally named. This paper describes 

only the Vantage Sandstone Member and the overlying members, as 

well as the lower part of the Ellensburg Formation, which is interbedded with the uppermost basalt member. The thick sequence of 

largely unnamed flows below the Vantage Sandstone Member is exposed only in the deepest gorges. The first few flows below the 

Vantage appear to be at least as extensive as the upper sequence. The 

flows have characteristics that make them distinguishable from the 

overlying sequence. Among these characteristics are smaller columns, 

different shape and type of vesicles, more spiracles, and more pillow 

zones.

The thickness and number of flows within the basalt members overlying the Vantage Sandstone Member differ from place to place. One 

of the reasons for the differences is the accumulation of more flows 

near the center of the plateau, where subsidence continued during ex212-527 66 2
G6 CONTRIBUTIONS TO STRATIGRAPHY

trusion of the basalt. The individual members have been mapped in 

only part of the Columbia Plateau; so, their total extent is not known. 

The members that constitute the upper 1,200 feet of Yakima Basalt are 

briefly described in the pages that follow:

VANTAGE SANDSTONE MEMBER

The Vantage Sandstone Member was named by Mackin (1961, p. 12) 

from exposures in readouts along old U.S. Highway 10, at the mouth 

of Schnebly Coulee in the SE^NW^ sec. 19, T. 17 N., R. 23 E., 1 

mile west of the old Vantage bridge (fig. 4). The member consists of a 

distinctive medium, friable, quartz-feldspar-mica sand, or of a weakly 

cemented tuffaceous sand, silt, or clay containing hornblende. At most 

places, thei arkosic sand is overlain by tuffaceous sedimentary rocks. 

Poorly'preserved carbonized twigs and plant impressions commonly 

occur in a black earthy zone near the top of the tuffaceous unit. The 

member is oxidized to pale yellow where exposed and is reported as 

blue or green in the subsurface by water-well drillers.

The Vantage Sandstone Member is about 35 feet thick in the Vantage-Priest Rapids area and thins northeastward to about 2 feet near 

the Bacon siding, approximately 10 miles northeast of Soap Lake.

FRENCHMAN SPRINGS MEMBER

Mackin (1961, p. 12-21) named and described the Frenchman 

Springs Member from excellent exposures in Frenchman Springs 

Coulee (fig. 4), where two flows and the Squaw Creek Diatomite Bed 

are present.

BASALT FLOWS

The Frenchman Springs Member contains two to six basalt flows. 

Of these, the three flows comprising the member in the VantageSentinel Gap area were named for nearby localities. The lowermost 

flow, the Gingko, was named by Mackin (1961, p. 13-14) after the 

G-ingko Petrified Forest; its type locality is in the lower part of Schnebly Coulee west of Vantage (fig. 4). The overlying Sand Hollow flow 

was named (Mackin, 1961, p. 15-17) for a tributary valley on the east 

side of the Columbia River valley nearly opposite Vantage; its type 

locality is in the cliff exposures just north and south of the tributary 

mouth (fig. 4). The uppermost flow in this area is the Sentinel Gap 

flow (Mackin, 1961, p. 17-21), named for the water gap through the 

Saddle Mountains. Its type locality is immediately south of the mouth 

of Sand Hollow. This flow terminates about 2 miles north of Sand 

Hollow and therefore is not present in Frenchman Springs Coulee. 

The three flows and additional unnamed flows exposed east of Connell 

make up the member within central Washington.
YAKIMA BASALT, ELLENSBURG FORMATION, WASHINGTON G7

R. 17 E. R. 18 E.

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TYPE SECTIONS

B Beverly and Saddle Mountains Members SC Squaw Creek Dlatomlte Bed

PR Priest Rapids Member SG Sand Hollow and Sentinel Gap flows

Q Qulncy Dlatomlte Bed V Vantage Sandstone Member and Glngko

R Koza Member flow

F. Frenchman Springs Member

FIGURE 4. Location of type sections (x) of Yakima Basalt.

The Frenchman Springs basalt is dark gray to black, medium to fine 

grained, and sparsely porphyritic; it consists of plagioclase, monoclinic 

pyroxene, olivine, opaque minerals, and a large quantity of glass (Waters, 1961, p. 602, sample 10). The plagioclase phenocrysts occur as 

single crystals or in clusters and are usually equidimensional, ^-^ 

inch in diameter. These phenocrysts are unevenly distributed accumulations may occur anywhere in the flow. The concentration of 

crystals ranges from several per square foot to one in several square 

yards.

At Frenchman Springs Coulee, the Frenchman Springs Member 

is about 250 feet thick; it is thinner to the north and northeast. South
G8 CONTRIBUTIONS TO STRATIGRAPHY

of Vantage, where the Sentinel Gap flow is present, the total thickness 

increases to about 375 feet, and this thickness appears to be consistent 

eastward.

The basal part of the Frenchman Springs Member consists of a 

widespread zone of pillows and palagonite that is 50-75 feet thick in 

the Vantage-Priest Eapids area. This part of the member is best 

exposed in a highway cut at the junction of Sand Hollow and the 

Columbia River valley. The pillow-palagonite zone has been traced 

northeast into lower Grand Coulee, 4 miles north of Soap Lake, where 

it is 20 or 30 feet thick. In places the zone contains much petrified 

wood that occurs as logs lying partly or entirely embedded between 

pillows or in palagonite. Nearly everywhere the zone is buried under 

talus.

SQUAW CREEK DIATOMITE BED

A bed of diatomite, which rests on the basalt of the Frenchman 

Springs Member, was named the Squaw Creek diatomite by Mackin 

(1961, p. 21) for exposures in the Squaw Creek drainage basin (fig. 

4). He interpreted the diatomite as having been "deposited in a lake 

impounded by the Sentinel Gap flow * * *"; on this basis he considered it equivalent to a part of the Frenchman Springs Member. 

This classification is used herein, and the unit is designated the Squaw 

Creek Diatomite Bed.

The easternmost known exposure of the Squaw Creek Diatomite 

Bed is in Frenchman Springs Coulee. In the Squaw Creek drainage 

basin, the bed is 5-17 feet thick; it grades westward into sandstone and 

pebble conglomerate composed partly of tuffaceous and partly of 

granitic detritus (Mackin, 1961, p. 21). In places where the Squaw 

Creek is not present, silicified wood or odd-shaped siliceous concretions mark the contact between the Frenchman Springs Member and 

the overlying Roza Member.

ROZA MEMBER

The Roza Member consists of two unnamed flows. The lower flow 

apparently is continuous over an area of thousands of square miles. 

This flow constitutes the Roza Member as defined by Mackin (1961, 

p. 21-23) in the Columbia River valley near Sentinel Gap and in the 

Yakima River canyon where he chose its type locality as "a scarp on 

the east side of the Yakima River opposite Roza Station * * *." 

(Roza station is a railroad siding in the canyon of the Yakima River 

between Ellensburg and Yakima (fig. 4).) This flow is a key stratigraphic marker throughout the Columbia Basin Irrigation Project 

area.
YAKIMA BASALT, ELLENSBURG FORMATION, WASHINGTON G9

The lower flow of the Roza Member is relatively uniform in thickness and composition; it has been identified as far north as Coulee 

City in the Grand Coulee, as far south as Pendleton, Oreg., as far 

west as the vicinity of Goldendale, and as far east as Coif ax, an area 

of over 20,000 square miles. The basalt is dark blue gray and weathers to a deep red brown, is medium to coarse grained and porphyritic, 

and contains plagioclase, monoclinic pyroxene; iron-rich olivine, 

opaque minerals, and glass (Waters, 1961, p. 602, sample 8). The 

phenocrysts are light-yellow or transparent plagioclase crystals that 

are lath shaped and average about 1 cm in length and 0.5 cm in thickness. The phenocrysts are uniformly distributed throughout the 

flow, averaging about five crystals per square foot.

The key lower flow is columnar through most of its thickness. The 

columns are 5-10 feet in diameter and tend to break into slabs and 

chips along platy joints normal to the columns. In many places 

these horizontal platy zones grade upward into a zone of swirling 

plates which characterize the upper part of the columns. Wherever 

the platy parting is well developed, the basalt is coarser grained than 

average, and plagioclase phenocrysts appear dark in the groundmass.

Overlying the lower flow from the Drumheller Channels and Connell eastward into most of Whitman County as far as Colfax is a 

dark-reddish-gray porphyritic flow. This overlying flow contains 

feldspar phenocrysts similar to those in the underlying flow; therefore, it is considered a part of the Roza Member (Bingham and Walters, 1965, p. 89). The reddish-gray flow ranges in thickness from 

55 to about 100 feet and is well exposed in Washtucna Coulee east and 

west of Devils Canyon.

In central Whitman County near Winona, many outcrops expose 

porphyritic cinders that have thin stringers of the upper Roza flow 

interbedded with them. These outcrops of cinders are considered to 

represent cones formed around multiple vents that provided lava for 

the upper Roza flow. In the floor of a scabland channel in the 

NW^SEi/4 sec. 10, T. 17 N., R, 39 E., the flow dips radially from a 

central cinder area.

The average thickness of the Roza Member on the east wall of the 

Columbia River canyon, where only the key flow is present, is 110 feet. 

The flow thins abruptly north of Potholes Coulee and gently along 

Upper Crab Creek valley. The member is over 200 feet thick in the 

Drumheller Channels, where both flows are present.

PRIEST RAPIDS MEMBER

Mackin (1961, p. 23-26) recognized four flows overlying the Roza 

Member at Priest Rapids Dam and named them the Priest Rapids 

Basalt Member. He designated the area upstream from the Priest
G10 CONTRIBUTIONS TO STRATIGRAPflY 

Rapids Dam (fig. 4) the type area and stated that flows occur there "in 

a south-dipping hbmocline on the west side of the reservoir." The 

Priest Rapids Member consists of the Quincy Diatomite Bed and four 

basalt flows. '

ftUINCY DIATOMITE BED

In part of the area, a bed of diatomite separates the Roza Member 

from the basalt of the overlying Priest Rapids; Member. This diatomite was designated the Quincy diatomite by Mackin (1961, p. 25- 

26)., because of its many exposures in. the southwestern part of the 

Quincy Basin (fig. 3), near Frenchman Springs Coulee (fig. 4) ? 

Mackin (1961, p. 26), stated "On the assumption that the Quincy lake 

[in which the Quincy diatomite was deposited] was impounded by one 

Priest Rapids flow and destroyed by another, the Quincy diatomite is 

considered to be a part of the Priest Rapids Basalt Member." It is 

herein designated the Quincy Diatomite Bed of the Priest Rapids 

Member. The area of many quarry exposures in the southwestern 

part of the Quincy Basin near the head of Frenchman Springs Coulee 

(Si/2 sec. 16; SE% sec. 17; NE% sec. 20; and Ny2 .sec. 21, T. 18 N., 

R. 23 E.) is designated the type area.

The Quincy Diatomite Bed is as much as 25 feet thick in the southwestern part of the Quincy Basin and as much as 35 feet thick on the 

south slope of the Frenchman Hills. The Quincy varies laterally, not 

only in the thickness of the diatomite, but also in the occurrence of silt 

and clay lenses, layers of banded opal, .and pieces of opalized wood. 

Northward and eastward from the type area the Quincy generally 

thins and may range locally from a few inches to about 6 feet.

The lake or lakes in which the Quincy Diatomite Bed accumulated 

must have been extensive. Even in areas where diatomite is absent at 

the base of the Priest Rapids Member, a zone of pillows and palagonite breccia as much as 10 feet thick is present. Many trees growing 

along the shore or floating in Lake Quincy were engulfed by the 

first flow of the Priest Rapids Member. These trees are now petrified 

logs or stumps, some in an upright position, within the pillowpalagonite zone.

BASALT FLOWS

Basalt of the Priest Rapids Member is grayish black, medium to 

coarse grained, and nonporphyritic, although some flows contain small 

phenocrysts easily noted in thin sections. Owing to a slightly dikty taxitic texture (Mackin, 1961, p. 23), basalt of the Priest Rapids Member 

weathers easily. Where freshly broken, a sample has a distinctive 

greenish cast, caused by altered saponite and chlorophaeite; where 

weathering has advanced, the basalt is mottled brown, and the outer
YAKIMA BASALT, ELtENSBURG FORMATION, -WASHINGTON Gil

surface is "a distinctive red brown. Spheroidal weathering appears to 

be more common iri the Priest Rapids than in other members.- . '

Acc6rding to Waters (1961, p. 602rsaniple;9), this basalt cbntains 

plagioclase,; monoclinic pyroxene, oliviriel glass, opaque minerals, and 

various decomposition products. The olivine-saponite content (12.5 

percent) is the largest of all samples from the Yakima Basalt reported 

by Waters. The percentage of glass (5.5 percent) is less than onethird that in the Roza Member and less than one-fifth that in the 

Frenchman Springs Member. .

The four flows of the Priest Eapids Member numbered by Mackin 

(1961, p. 23) at the Priest Eapids damsite have a total thickness of 

220 ±25 feet there. The member appears to thin northward and eastward and thickens to the south near Mabton;

SADDLE MOUNTAINS MEMBER

In the Ellensburg quadrangle, Smith (1903) originally named the 

basalt flow intertongued with the Ellensburg Formation the Wen as 

Basalt. More recently, Waters (1955, p. 673) found that "The Wenas 

basalt continues eastward from Smith's area [in the southeastern part 

of the Ellensburg quadrangle] into the Yakima East quadrangle." 

Waters (p. 673) also identified two other flows, the Elephant Mountain flow and the Selah Butte flow, that were interstratified with the 

Ellensburg Formation at higher stratigraphic levels than the Wenas 

Basalt.

On the basis of general lithologic similarity, the name Wenas Basalt, 

used by Smith (1903, p. 4) for flows in his Ellensburg Formation, was 

used for similar rocks in the Sentinel Gap-Saddle Mountains area by 

Taylor (1948, pi. 1) in his.open-file report on the Columbia Basin 

Irrigation Project area. Because the formations are not mapped 

across the intervening distance, the Vantage-Priest Rapids area is considered separate from the Yakima River valley, and the name Saddle 

Mountains Member of the Yakima Basalt is hereby assigned to all 

the basalt flows overlying the Priest Rapids Member in the Sentinel 

Gap area. At the type locality of the Saddle Mountains Member, 

southeast of Sentinel Gap (fig. 4), it consists of one flow (Mackin, 

1961,p.26).

One of the Saddle Mountains flows (the Pomona flow) and the underlying vitric tuff (a part of the Beverly Member) exposed on the 

Saddle Mountains have recently been correlated by Schmincke (1965, 

p. 275) with the basalt and sedimentary rocks mapped by Smith (1903, 

1904) in the Ellensburg and Mount Stuart quadrangles, and by Waters 

(1955) in the Yakima East quadrangle. Also, reconnaissance observations along Wenas Valley have revealed that in Kelley Hollow, Smith
G12 CONTRIBUTIONS TO STRATIGRAPHY

(1903) included basalt of the Frenchman Springs Member with that 

mapped as Wenas Basalt. For these reasons, the name Wenas Basalt 

is abandoned, and the name Saddle Mountains Member is substituted 

for all flows above the Priest Rapids Member in the Yakima River 

valley.

': Field reconnaissance, eastward and southward from Sentinel Gap, 

suggests that the Saddle Mountains Member includes several previously' unrecognized flows; rather"-than a single' flow overlying the' Beverly Member of the Ellensburg Formation as in the type section. Well 

drillers' logs also show that the Beverly Member is discontinuous laterally so that the Saddle Mountains Member rests disconformably on 

the Priest Rapids or Roza Member rather than on the Beverly Member in parts of south-central Washington. The basalt of the Saddle 

Mountains Member is petrochemically similar to the basalt of the 

Priest Rapids Member and is probably a continuation of the same 

great outpouring of basaltic lava as the rest of the Yakima Basalt 

(Waters, written commun., 1963). For this reason, the Saddle Mountains Basalt Member of Maokin (1961, p. 31), considered by him to be 

a part of the Ellensburg Formation, is herein renamed the Saddle 

Mountains Member and is reassigned to the Yakima Basalt, regardless 

of whether it overlies or is intercalated in the Beverly Member of the 

Ellensburg Formation.

At its type locality the single Saddle Mountains basalt flow is black, 

dense, very fine grained, and sparsely prophyritic. The flow is characterized by narrow, splintery columns and by hackly jointing in the 

entablature of the flow, and these characteristics may be so well formed 

that the colonnade is almost absent.

Much of the basalt is vesicular, the small spherical vesicles being 

1-2 mm in diameter. Most of the Saddle Mountains basalt flows 

range from black and hackly to light or dark gray and columnar. 

In some places, however, a flow may consist of an agglomerate of 

reddish subangular pebble- and cobble-size fragments.

Apparently at least one of the flows contains sparse large phenocrysts similar in appearance to those in the Frenchman Springs Member. Also, several flows have distinctive small transparent lathshaped plagioclase phenocrysts 2-4 mm long that are uniformly distributed through the flow six or more per square inch.

Flows of the Saddle Mountains Member have been identified north 

to the Frenchman Hills, eastward almost to Connell, southward to 

TJmatilla, and westward to the Yakima area. In the central part of 

this area as many as four flows have been identified.

ELLENSBURG FORMATION

The Ellensburg Formation (Smith, 1901, p. 17-22; 1903, p. 2-3; 

1904, p. 7; Waring, 1913, p. 19-21; Axelrod, 1950, p. 239-243; Waters,
YAKIMA BASALT, ELLENSBURG FORMATION, WASHINGTON G13

1955, p. 670-673; Mackin, 1961, p. 26-36; Smiley, ; 1963, p. 169) is 

composed of 2,000 ± feet of continental pyroclastic and sedimentary 

deposits that interfinger with the uppermost part of the' Columbia 

Kiver Group the Saddle Mountains Member of the Yakima Basalt 

in the northwestern part of the Columbia Plateau. In a report describing the geologic features of a part of Yakima County, Smith 

(1901, p. 17) said .that "Lying directly upon the [Yakima] basalt is 

the sedimentary series to which the name Ellensburg formation has 

been given." Smith was following a usage introduced earlier by 

Eussell (1900, p. 127), who said that the Ellensburg sandstone of the 

Kittitas Valley "rests on a sheet of lava." Smith, however, qualified 

his statement by adding that "in the larger part of the North Yakima 

area * * * some of these sediments were laid down before the eruption of the last flow of the basaltic lava * * *."

According to Foxworthy (1962, p. 19), the age of the mollusks and 

vertebrates indicates that "the main body of the Ellensburg formation 

probably was deposited entirely during the Pliocene epoch * * * 

[and] the uppermost flows of the main body of the Yakima basalt 

probably are of early Pliocene age." On the basis of fossil evidence, 

Smiley (1963, p. 206) has determined the age of the Ellensburg 

Formation to range from late Miocene to early Pliocene.

BEVEBLY MEMBER

The Beverly Member at the type locality southeast of Sentinel Gap 

(fig. 4) in the NW*4 sec. 23, T. 15 N., E. 23 E. (Mackin, 1961, p. 26) 

consists of beds of quartzite-bearing conglomerate, pumicite, and 

^iffaceous sand, silt, and clay. At Sentinel Gap, the quartzite-bearing 

conglomerate and the pumicite compose about 160 feet of the total 

300 feet. The member is known to extend eastward as far as the 

Drumheller and Othello channels and southward as far as Umatilla. 

In the scattered outcrops the member may include basaltic f anglomerate, as well as conglomerate, pumicite, tuffaceous sand, silt, and clay. 

The Beverly Member may be considered a lithesome (Wheeler and 

Mallory, 1954, p. 929), consisting of mutually intertonguing lithostratigraphic units, any one of which may predominate or be present 

to the exclusion of the others at one locality. The time-stratigraphic 

significance of these lithostratigraphic units to one another has not 

been determined.

The 200=t feet (Smiley, 1963, p. 169) of sedimentary deposits underlying the Saddle Mountains Member in the Yakima area was 

named the Selah Tuff Member of the Ellensburg Formation by Mackin 

(1947, p. 33). In 1961, Mackin (p. 26^31) named the 300± feet of 

sedimentary deposits and basalt flows under the Saddle Mountains
G14 . CONTRIBUTIONS TO/STRATIGRAPHY . , :

Member at Sentinel Gap the jBeverly-Member of the Ellensburg 

Formation. The name Beverly Member is here given to the.sedimentary deposits below the top of the uppermost Saddle Mountains 

flow and above the Priest Rapids Member. The name Selah Tuff 

Member is abandoned.

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Axelrod, D. I., 1950, Evolution of desert vegetation in western North America,

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Bingham, J. W., and Walters, K, L., 1965, Stratigraphy of the upper part of the

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Calkins, F. C., 1905, Geology and water resources of a portion of east-central

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Smiley, C. J., 1963, The Ellensburg flora of Washington: Univ. Calif. Pub. in

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Smith, G. 0., 1901, Geology and water resources of a portion of Yakima County,

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Survey open-file report, 182 p.
G15

Waring, G. A., 1913, Geology and water resources of a portion of south-central

Washington: U.S. Geol. Survey Water-Supply Paper 316,46 p. 

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the Takima East quadrangle: Geol. Soc. America Bull., v. 66, no. 6, p. 663-684. 

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o