hkcFairl3mm Geography and Land Studies Department

CeaM Washington University Ellensburg, Washington

~ ~ a m Q c w u . ~

Faculty Advisor Dr. Karl LiDqukt @mgragBy and Land Studies Depammt

Central Washington University Ellmburg, Washington

lillquis@cau.edu

Figure I . Location rnajfiof%dy area

2. Physiofiaphic map

3. Inundation map of Quincy Basin *.>

4. Oblique ground view % f ~ e o r ~ e Gravels, , 7 .

5. George Grapels 4

6. An example of weathered scbid$& : Gravels

7. Map of George channel*f;owrrrs I U L ~ U U I I VL Seorge Gravels

8. Annotated rn, of bash and butte topography

9 0bliqrp8grouna vlew of stripped structural bedrock terrace n, 10. Map view of stripped structural bedrock terrace

I 1. Map view of kolks

12. Oblique ground view of kolk

13. Map view of plunge pools

14. Mosaic oblique ground view of plunge pools

15. Map view of crescent-point bar

16. Map view of pendant bars

17 Mosaic oblique ground view of pendant bars

18. Map view of expansion longitudinal bar and pendant bar

19. Oblique ground view of current dunes from southwest

20. Oblique Ground view of spalling basalt corestone

21. Physical and chemical weathering on interfluve surface

22. Talus mantling fosse side of crescent-point bar

23. Large block rock fall on Babcock bench

24. Oblique ground view of rotational landslide block

25. Map view of undifferentiated landslide scarp

26. 1962 U.S,D.A. airphoto of the Potholes Coulee

Tables

Table 1. Giant current dune frequency

Abstract

]introduction

Study area

Background

Methods

Geomorphology

Fluvial Features

Potholes Coulee

George Gravels

Basin and Butte Topography

Kolks

Plunge Pools

Bars

Current Dunes

Weathering Features

Physical Weathering

Chemical Weathering

Composite Weathering

Eolian Deposition

Mass Wasting Features

Rockfall

Landslides

Solifluction

Biotic Geomorphic Features

Flora

Fauna

Humans

Conclusion

Literatures Cited

Abstract

The Potholes Coulee is located on the western margin of Quincy Basin,

Washington about 15 miles southwest of Quincy . Potholes Coulee has been shaped by

various geornorphic processes and agents since the Miocene epoch creating a unique

landscape. The bedrock of the basin is Miocene Columbia River flood GasaIt folded by

Pliocene tectonic forces and shaped by catastrophic flooding events of Pleistocene era

(Bretz, 1923). Quincy Basin was a depositionaI (fluvial and eolian) and erosional region

of the Missoula floods during the late Pleistocene epoch (Bretz, 1928). Miocene

Columbia River Basalts were folded, and then eroded by Pleistocene glacial outburst

flood events. The western margin of Quincy Basin has three eroded outlets through

Babcock/Evergreen Ridge. The Babcock and Evergreen Ridges are separated by Potholes

Coulee. Potholes Coulee is a relict landform characterized as a headwardly eroded

cataract. Grolier (1965) describes the coulees as existing prior to the Missoula Floods

based on the flood gravels indicating a western source in Quincy Basin. The cataracts

contain late Pleistocene Missoula flood crystalline and basalt gravels as various

landfoms. The flood sediments are capped by a weathering mantle, eolian deposits, and

mass wasting debris. The Columbia Basin Irrigation Project during the 1950's enabled

increased settlement in the area adding humans as key geomorphic agents. In the early

19503, Ancient Lake cataract was flooded, filling the cataract with a temporary Iake,

leaving a rime indicating the past shoreline.

Introduction

Potholes Coulee has been shaped by various geomorphic processes and agents

since the Miocene epoch creating a unique landscape. The bedrock of the basin is

Miocene Columbia River flood basalt folded by Pliocene tectonic forces and shaped by

catastrophic flooding events of Pleistocene era (Bretz, 1923). Quincy Basin was a

depositional and erosional region of the Missoula floods during the late Pleistocene epoch

(Bretz 1928). After nearly a century of research, many questions remain regarding the

geomorphology of the Quincy Basin, and specifically the Potholes Coulee (Figure 1).

The primary focus of this paper is to describe the geomorphology of the Potholes

Coulee and adjacent Babcock Bench, as well as to provide geomorphic context to late

Pleistocene sloth remains unearthed at Bishop Springs (Figure 2). Secondly, I will

describe future research possibilities in the area. The overall intention of this study is to

provide further insight to the geomorphology of Quincy Basin and the Channeled

Scablands.

Study Area

The Potholes Coulee is located on the western margin of Quincy Basin about 15

miles southwest of Quincy (Figure 1). The Potholes Coulee is situated 134 meters above

and 1.5 kilometers east of the Columbia River in sections 7, 8,9, 18, 17, 16, T. 19 N., R

23 E., W.M., of the Babcock Ridge, Washington United States Geological Survey

(U.S.G.S.) 7.5 minute quadrangle. The rim elevation of the coulee varies from 41 1 to 320

meters elevation with the floor of the cataract varying from 250 to 308 meters elevation.

The Potholes Coulee consists of double horseshoe cataracts bisecting Babcock Ridge and

Evergmn Ridge along the western margin of the Quincy Basin (Figure 2). The rim of the

cataracts opens to the west onto the B h k Bench above the Columbia River.

]Figure 1. Loration map, the M y ama is bated -15h wlrthwezt of George aad -Mkm sonthw& of Qdncy. (Map derived from US.GA DEM)

The bedrock consists of tJw, CoIumbia River Basalt Group (CRBG's) with

diatomite and sandstone interbeds. The Rosa flow, Babcock Bench flow and two Ginkgo

flows of the Frenchman Spring member of the Wampum basalt p u p and Vantage I

Sandstone are exposed (R.D. IBentIey, personal communication, May 2003) to the level of ;I1 & L . I L .

- 4 the Babcoek Bench. The Babcock Bench consists of the Gnrnde Ron& N2 group of the

I

CRBG' s. Loess and cover sand caps glacio-fluvial deposits flooring the cataracts. Brown

tuffaceous sand and platy caiiche capped by I w s cover the Babcmk Ridge and

Evergreen Ridge (Grolier, 1 965).

The region is characte* a semi-arid, continental setting. At Quincy, from

194 1-2002, the maximum average annual temperature was 17" C and the minimum

average mud temperature 3' C; with July behg 30.1' C, and January king -7' C.

The average annual precipitation was 22.3 centimeters, with the majority of precipitation

occurring in September, November, December and January. The region receives an

annual average of 33 centimeters of snow (www .wnx.dri.edu, March 2003).

Rgum 2. Physiographic map s b w & Potholes CoPrlee, locsted on the w h mmrgin d m y Basin,errstoitber ' " River. N o & d m b l e b o ~ ~ w i t h ~ v e s e p a r a t i n g t h t w o catamcta (Map derived Rom U.S.G.S. DEM)

Five welldrained Aridisols formed on the diverse terrains of Potholes Coulee.

Gentry (1984) describes the soils as follows:

I. Ephrata sandy loam: a sandy-skeletal, mixed, mesic, Xerollic Camborthid soil;

found on 5- 1W slopes, forrned on subfluvial gravels at the mouth of the Ancient Lakes

cataract.

2, m a cobb1y sandy loam: a sandy-skeletal, mixed, mesic XemIlic

Cmborthid soil; found on 0-15% slopes, fmmd on the sub-fluvial bm deposits within

the Ancient Lakes cataract.

3. Mdaga very stony smay 1oam: a sandy-skeletal, mixed, mesic XeroUic

Camborthid soit; fwnd on 0.35% slopes, formed on sub-fluvial bar depusits widin the

Dusty Lake cataract.

4. Starbuck-Bakeoven-Rock outcrop complex: a loamy, mixed, mesic, Lithic

XeroIlic bborthid soil; found on 045% dopes, fonned on basalt bedrock along

Ba-k bench and Evergreen Ridge.

5 . Starbuck-Presser complex: a loamy. mixed mesic, Utbc Xerollic Cambortbid

soil; found on 0-258 slops, formed on basalt dong the northlnorth east rim of Potholes

CouIee.

The vegetation is primarily bluebunch wheatgrass, cheat grass, with big sage

brush, rabbit brush, hapweed, and herbaceous shrubs.

Historic laud uses include human habitation, cattle range, and limited agriculture.

After the implementation of the Columbia Basin Irrigation project in the early 1930's,

bay farming and subsequently archads and various crops became a major land use on

Babcock Bench. At present, the Potholes Coulee is a Washington State Fish and WildIife

managed area and the majority of land use w i t h the study area is recreational

(equestrian, biking, hiking, and fishing).

Miocene-Pliocene E m h s

Between 6 ma. to 17 IxLa many flows of Columbia River Basalt Group magmas

flooded eastern Oregon and s o u ~ t e r n Washington. They originated from fusures in

eastern mgon and southatem Wasbingtoh The flows are charactebd as having a

blocky entablature cap on colonnade with a pillow structured base. The flows are

inkmittenfly bedded with Ellemburg Formation detritus and diatomaceous sediments

-kin, 1%1: T o h et a1989). The CRBGs w a then folded from the west then

south by Phacene tectonic form crearing ridges and basins. Subsidence of the plateau,

uplift of the Cascade Rmge, and plunge associated with regional folding are three

possible causes of deformation. The Columbia River continued flowing through the

region but was diverted at d i f h n t locations and times, The s t w t u d Quincy Basin was

formed through these events and is bound to the north by the Beezly Hills, the west by

Babcock Ridge and the south by the F~nchman Hills (Mackin, 196 1 ; Watters, 1989).

The Columbia River flowed along the western margin of the Columbia basin in

its present course eroding through the CRBGs creating Balm& Bench. Two separate

occasions of rising anticlines from the tectonic forces from the south were thought to

temporady dam the Snake River and Columbia River creating h k e Ringold (Newcomb

1958). The hpowded Columbia River Ieft fluvio-lacustrine deposits, known as the

Ringold Formation, from sauth in the Pasco Basin to north along the rim of the

Babcock/Evergreen Ridge (Grolier ztnd Binglum, 1978).

Pleistacene Emch (The Channeled Scablaads)

The Chamled Sc&1ands of the Columbia Basin are relict landforms of outburst

floods from Late Pleistmne glacially dammed Lake Missoula (Bretz, Smith and N e e

1956). Many huge catastrophic oatburst floods (jakulhhps) from Lake Missoula

e x W the capcity ofthe existing drainage system of the Columbia River with thr:

flood water flowing up to 2,500,000 m3 through the Columbia Bash (Wgtt, 1985). More

then 30 £loads d between 12,700 and 15,300 yem before present (y.b.p) based on

tephrichnology and radiocarbon dating (Waitt, 1985). The flood waters flowed across

north W m into north Washington k f o e enwuntering the Ohogan lobe of the

Cordilleran Xce Sheet which diverted the waters south into the Grand Coulee and into the

Quincy Basin.

The water pooIed in Quincy Basin before exiting through four outlets. There

were three d e t s on the western margin of Quincy Basin ( C m r W e e , Potholes

Coulee, and Fmchman Code) and one to the southeast (Dmnheller Chmls) at the

eastern margin of tb Fbnchman HiUs (Figure 3) (Bretz, 1930). When the Okanogan lobe

was not in place, the flood waters flowed down the Columbia River -age and into

Quincy Basin via Crater Coulee and Potholes Coulee (Bretz, Smith and NeR 1956).

During intervals of lower magnitude floods, the waters flowed out the more hydmhcally

favorable Dmdeller Channels to the east (Bretz, 1928).

I 1 I I 1 I I I 1 0 22.5 25 SO Kilometers

Legend s

Elwath wedm

r- High : 2870 metsrs Direction of flood waters F.C. - Frenchman CouIee L.QC. - Lower Grand Coulee D.C. - IhmhelIer Channels C.C. - Crater CouIee B.R. - Babcock Ridge - : m P.C. - Potholes Coulee E.R. - Evergreen Ridge

f

-3. ~ k m h u a d a l o n d d Q l r l n c y B a s l b n ~ t h e ~ d ~ ~ t e s t ~ b ta%te Mhmh Tlw --water mrrrlt b Qldncg Basin was 409 m adapted h m Baker (1973). (Map derived fmm U S G A DEM)

The catastrophic floodiog crated an amazing anastomising cumglex in

the bedrock mretz, 1923). The abandoned catarads are described as resulting from sub

fluvial plucking of the columnar basalt by vortices and -porting the blwks

downstream by the extremely competent flow during the l&gst flood events (Bretz

f 930; Baker 1974). The eroded bedmk features are divide crossings, coulees, b u m and

mesas of basalt and kolks (i.e. eroded hollows). b s was eroded creating smadhed

"loess islands". The floods are further evidenced by subfluvial mega-bed form, such as

various bars and giant lcurrent dunes (Bretz, 1927). After flowing through Quincy Basin,

the waters pond4 behind a hydraulic constriction formed at W d d a Gap in the Horse

Heaven Hills forming temporary Lake Lewis with a depth of 350 m. O'Connor and Baker

3 1 ( 1992) calculated the flow through Wallulzt Gap at 10 W o n m /s* , a discharge greater

than any rivers or flaading events previously or since. Waitt (1995) notes smaller

flooding events down the Columbia post dating late Pldstocem Lake Missoula Floods.

m€hwls

This r e s m h was accomplished thmugb document review, interviews,

Geographic ~rmzttim System (GIs) W q u e s , airphoto analysis, and field w o k I

fmt reviewed past literature that describes regional and local pmo'phic processes and

f-rs, landforms, historic use, and recent occapatim to better understand the parameten

of the stcldy area 1 interviewed a resident of mare than 50 years, Dave Bishop, to

understand the role of recent human occupatim at the site. The spatid and ternpard

parameters for the project were decided with understanding the past research.

1: l2,OOO 1949 and 196 1 U.S. Department of Agriculhm and 1996 1:24,000

U.S .G.S. digital orthophoto quads were compared to gauge the rate of environmental

change since the Columbia Basin Irrigation Roject . I then used U.S.G.S. 1:24,000

topographic maps, airphotos, and ArcGIS by Environmental Systems Research Institute

(E-SIU) to identify and analyze key Imdfom and plan field trips for field checking of

those features.

Eeld observations and field checking of observed remotely sensed data was

comp1ete.d from July, 2002 - May, 2003. GPS techniques wete used to locate various

attributes to better interpret hdfoms in the field such as chod length on possible sub-

fluvial Worms. Once identified, the various geomorphic agents and d t i n g land-

forms were mapped onto copied airphotos and topographic maps in the field. In the

C.W.U. GIs lab the measured observations were entered into tbe computer by

downloading GPS coordinates into ArcGIS and digitizing field observations and

Mbutes as poiygons in AEGIS. The polygons were then used in slope process

modeling using ESRI Spatial Analyst to better understand the pmxsses that may have

occurred on the sIopes since initid deposition. Comparisons between the computer's

modeled pdictiom versus field obsedons were made. Obsewd historic and p m a t

pmorphic processes and factors were mapped using ESRI AEGIS.

The various geomorphic processes and factors were c a t e g m d in a relative

temporal and spatial hierarchy beginning with the formation of the primary landform

(Potholes Coulee) of the study area and finishing with the merit advent of humans to the

region. This classificdon is bast4 on the order of landform origins hived from an

application of Steno's Principles and observed physical evidence.

Geomorphology

Fluvial Features

Potholes Coulcg Grolier (1965) describes Pothales Coulee as a sag in the

BabwM3~ergnxn anticline that was subsequently m&ed by Pleistocene flood waters

flawing down Grand Coulee into Quincy Basin. These ftoad waters then fl~wed out

through the sag rejdning the Columbia River. Potholes Coulee, s h h to Nagam F a j

formed by head-ward erosion by subaqueous undercutting then twwport of sediment

down flow as waters from the Quincy Basin flowed though the bmxh to njoh the

Columbia River (Figure 3) (BE&, 1930; Grolier, 1965; Baker* 1973). The fluvial event,

that formed Potholes Coulee, appears to be ephemeral as there are no visible channels

coanecsting the mouth of lower Grand Coulee (northeast) to Potholes Coulee in the

southwest. The events attributed to the f ~ m t i o n of the Iandform m the late Pmtocene

L r r k ~ Migsoda Hoods (1 2,7@15,300 ybp) @re@, 1930).

Georere Gravels and Gtwrp:e Chamel: Potholes Coulee appears to have an origin much

earlier then vtbe late PIeistocene as older, extwbsind, flood sediments (C*seorge Gravels)

are found in a channel (George Channel) ~~ to the s o u t h s t from Potholes Coulee

into Quiicy Bash. Thou&, it is evident the catafact formed as waters flowed down

Grand Coulee into Quincy Bash a d out the Potholes Coulee from the nmtbst ,

pbab1 J mmmhg as arIy Pleistocene flood waters, Gmlier (1965) M b e s the

coulees as existing prior to the late Pleistocene Miamla Floods based on the flood

gravels indicating a western source in Quincy Basin (area, Smith, and Neff, 1456).

Bretz (1969) noted the massive capped flood sediments (the George GraveIs) Bowing up

the Crater coulee and Po€hoIes Caul= as pm-w~wnsin (80,W ybp) flood deposits

Figure 4).

~ + U W p e ~ ~ d ~ Q ~ & ~ ~ p i € m m ~ ~ ~ ~ : l ) ~ G r a ~ & ~ ~ ~ a ~ r n ~ l g ~ r ~ a t ~ ~ ~ ~ ~ o f l O % Ha. 2) Gmt~pbrCedGeage-

The George Graoda slre a ~)nglummtc cooaposed of extremely weathered basalts with

pdagonite, pigs, =hist, q d t e and granite cobbles with imbridom indicating a

we&em source (F~gruep 5 & 6). The gravels are ~apped by a 1.5-m of MCW (Baker,

1973; P e n and Nummdd, 1978). BjmW, Frecht and Huhar (2001) m@b tbe

George Gravels w nimilrt in age to the Old Maid Coulee gravels, having a reverse

magnetic palaity indicating an early Pleistocene (Brunhes-Matum 7gQ,OOD ybp) w. Though the George Gravels have imbrications hdiclitlq a wstetn source it is evident

they post dstc the c m t ' s f o d o n by early P l e h n e flood watus issuiog 6om

Gtand Coulee.

The George Channel has a northwest to southeast tmd coming from the head of the

Potboles Corrlee to the southeast and contains the George Gavels (Figure 7). The

camacts had to be formed by w m flowing from the norbat prior to genesis of the

channel and deposition of the George Gravels. The implications are intriguing but are in

need of detailed resear~h on the George Gm~els and the sediments within the Potholes

C Q U ~ . A some for flood waters mqeknt enough to crate the landform is in

question as it predates the late Pleistocene Glacial Lake Missmla Alkfnate wakr

s o w could be pal80-gkial lakes since obliterated by subsequent gIacia.1 advances, or

multiple johhhups (sub-glacial outburst flood) from Olranogaa, region of British

Columbia (Shaw et. al1999; Lasemum and Shaw 2000% 2000b; Mate and Levson 2000).

4 u

~~ F ~ t a I ~

I m:- @ GmQeQmvak* ~ h f O ~ m: If*

F ' i g m ? . ~ d e w 3 G e o ~ ~ ~ ~ ~ ~ ~ r m d t S e ~ h ~ M* the dIrectIon ddmpmd h d b g nwthw& to sw- and b t I o n of the George Gmv& (Map W e d from U.&G& DEM)

Basin and Butte Tmmohv: Basin and bum topography is a tern describing generic

scabland topography consisting of various scales of eroded hndforms resulting from

regional catastrophic flcgd activities. This topography was created by flood waters

abrading and plucking, 1s mistant k h x k Ieaving terrace, channel, bk, and butte

l m d f m that range in she from ~1 meter to humbtds of meters (Egure 8). Buttes are

localized areas of s h a ~ ~ &f that d d u a t e in a flat Wle" top surface tkt ranges from

a fbw metas to thousands of.metm in volrune. Basins are eroded ~ t o ~ g channels,

terraces or k o h .

Stripped structural bedroclr temm .am fa& at the heads awl margins of the mtmcts

by turbulent waters rhrough &aqueous undetz:ming, vortices plwkhg then m r t of

the sediment down flow by the exlmmdy competent flow of catastrophic flood waters.

The do&s of the basalt are plucked leaving the more resistant entablature cap of the

lower flow to form long, broad, planar terraces (Figures 9 & 10). Striped structural

bedrock tenaces indieate an extremely high magnitude and competent idiluvid o m .

The featms vary in area from 33,150m2 - 529,200m2, and are 15 m - 67 m above the

cataract floor and are up to 53 m deep. They are capp i by a shallow tu well developed

weathdug mantle and 1- (5 cm to > 2 meters), Some terraces are well shelterd from

wind creating eolian deposition hollows which support a variety of flora and fauna.

S o m e o f t h e ~ d o n o t a p p e a r c o h a v e b n ~ ~ ~ d y b y t h e l ~

Pleistmxne fi& as idhkd by thi: d e v e l ~ t of the wtathering mantle md lichen

growth on exposed hdmk

" i t

Kolks: K o k are formed in turbulent waters by sub-aqueous vortices exploithg localized

wedmesses in the entablature cap d g "pitsM (Balrer, 1973). Kolks are similar in

morphology to plunge pools, save in the study site, they are located in areas up d down

flow from the cataracts heads. K o h f o n d in bedrock indicate an extremely high

magnitude and competent flow at time of origin (Baker, 1973). Some of the larger k o b

(diameter IOm, depth > 1Om) cut through the e ~ 1 ~ cap, tbea into ttte colonnade

W o w and have potential to be depositional hollows tbat can provide datable materid in

form of tephra, organic material atrd laws pigum 11 & 12). The k o k on the interfluve

between the cataractg are formxi on different surf- with some king breechad d h g

c ~ . f o m a t i o n .

Figure11. M a p r l m o f L d h ~ t e d m t b e ~ e l A w . c m ~ a L . L c d h t y W r c cataracts. MotatBom: 1) the same kdk as in F ' i 12. 2) B& kolk on Atldent Lake side of iuteduv& (1996 U.S.G.S. digitaI ortho- q d )

Pluage Po&: Plunge p i s formed down flow at the heads of the cataracts as a result of

sub-fluvial erosion and transport of s d h n t or bedrock at the base of waterfalls (Figures

13 & 14). The plunge pools within the heads of the Ancient Lake and Dusty Lake

cataracts are formed in bedrock though there is a '"mispked" plunge pool near the

mouth of the Ancient Lake cataract that f o n d early jn tbe cataract formation. The

plunge pwls generally have bars mantle the plunge pool floor, as well as, extending

down stream from them. The plunge pols in the hertds af the catarm contain water

from the CoIumbia Irrigation Project; having an elongated to circular morphology

with the long axis indicating direction of flow, and no distinct volume. Plunge pools

Nustrate the fluvial origin by which Pleistocene flood waters once flowed through these

cataracts before rejoining the Columbia River.

~ 1 3 . ~ b o f p h u r s e p o o l b f o r m e d k M s e d i m e n t & a h e ~ o f t b e b e a d s J Ancient h k e and DClsty Ldw ~~ N h r P) Rmge pod (1% US.G& digital claad)

Figure 14. M d obl e gromtd view of p- PIS Iacated at the b d ~ d Amdent lake a d

Bars: The cataracts are f l d by glacio-fluvid deposition with bar morphology. A bar

is a streamlined deposition pointing in the direction of flow. A fosse, an elongate, eroded

hollow next to the cataract wall, forms where water depth, channel topography and

hydraulics allow for deposition of sediment. . The bars are classified based on

morpho~ogy and depositional location. The bars of the study site are categorized as: 1)

crescent-point bar, 2) pendant bar, and 3) expansion-longitudind bar (Waitt, 1994).The

bars consist of a mixed lithology of sub-rounded to angular sand and cobble sized basalt,

quartzite, schist, gneiss, rip-up clasts of calcrete, calcmte coated basalt, petdied wood,

palagonite clasts with the mode being basalt, There are also angular basalt boulders with

an intermdate diameter >1 m.

Crescent-point bars, s i d a r to point bars in morphology and deposition, form on

the lee side of a bend in the channel, with or without an obstruction or a slowing of flow

(Waitt 1994). Great crescent bars rising more than 30 meters above the Babcock Bench

and more then 720m long formed on the southeast edges of the mouths of both cataracts

of Potholes Coulee (Figure 15).

~ 1 5 * M s p ~ o P ~ - ~ ~ b a r s c w ~ ~ d t h e m o * o f ~ a n d W M W E B ~ , ~ ~ bp -<imus~a agi~al orth~plmpto

Pedant bars form on the lee side of an obstruction or spur on a channel wall

extending down current and are named for rhe way a pendant hangs from one's neck

(Waitt 1994). Pendant bsus have formed along the north and south in the Ancient Lake

Cataract and north side of the Dusty Lalre cataract. The bar on the north side of the

Ancient h k e catamct rises >30m above the cataract floor and is more then 2.25 km long

with tdus partialiy to comp1etety fillirrn the fosw side (Figures 16 & 17). F w t h , the bar

was mworked to form plunge pooh at the head of the eatmct. The bar dong the south

wall of the Ancient M e catatact experienced 3 bar budding events evidenced by bee

pronounced ?errace like" f m on the north side of tha bar. This bar complex rises

>3Om above the ccataract flaor and is more then 1.25 Zrm long with a mass wasting block

and talus H h g the fom side of the bar and is mwoW to form plunge p l s at the head

of the cataract. The pendant bar on the north side of the Dusty Lake cataract formed on

the down current side of a channeI spur and rises >15m above the cataract floor and is

more then 1 km long with talus partially fiIling the fosm side of the bar.

Figwe 17. Mmak oblique ground view of pendant bar along north side of the Ancient Lake cataract taken from h i e r f b e to the south. Note cammt &me train on the s d side of tbe bar, evaporite '~,andplmgeporSintltebersdof thecataract to &east.

l%psiWon@tudinal. bars axe formed in side channels or mid-channe1s with or without

obstruction or chamel widening (Waitt I*). The expmsiodon@tudinal bar in Dusty

We Camma f o n d at a widend section mid-channel, Tbis bar rises >10m h v e the

c&m& floor and is more then 2 km Ibng with talus partidy W g the fosse sides and a

plunge pool awed in to it at the hehe of the catarmt ( E g w 18).

Cuxrent dunes: Current dune features have ripple morphology and atse formed by wata

flowing over workable sdbmt at a specific depth and velocity. The current dune

features are lwated on the south side of the pendarat bar dong the north wdI of the

Ancient Lakes cataract (Figure 19). The dune train is >1.5 km long forming on slopes

< 1s" trending east-west with the dunes muding north- south lOOm long and have an

average chord of 23 m and a mode of 17 m with surface amplitude < 1 m (Table 1). The

rnorph010gy, wruate shnpe and sub-cxiticaily climbing dunes of the feature indicate

direction of flow hrn the eat. The coarse sediments on the surface and in the m n t

dunes indicate st fluviaI origin.

Giant Current Dunes Dune Chord (m)

1 35 2 41 3 41 4 41 5 43 6 30 7 19 8 1 S 9 18

10 17

Giant Current Dunes Dune Chord (m)

22 20 23 27 24 12 25 28 26 30 27 17 28 17

Statisties Sum 948 Average 23 Made 17 Median 19 Minimum 12 Maximum 43 Std. Dev. 8.647Q74

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Chemical and physical weathering both occurs within the study site &pW

being discretely cat ego^ they often occur simahanesusly. Physical and &eW-d

weathering enable e&h other: for example, physical weatbring mates more s H & @

area, thereby enabling chemical weathering to mur. Furtherp chemical weathering

weakens the substrate enabling physical weathezing to wuf. Bath forms of d&&

occur at present. I : ' , ..

, , I , - I in i .. 1 1 . . b . . ' A t

PhvsicaI Weathering: Physical weatbering is the degradation of rock via mechanical

means, often with more hen om mechanism occurring at once. The domimat form of

physical weahzing at the site is a composite af thermal expansion-contraction (freeze-

thaw) and f b t wedging. This weatkhg wcurs at locations of bedrock exposed by

f l d w a k r s and on cliffs and horizontal surfhces with maximum surface area exposed to

the environment. Fmm-thaw shattahg and wedging enables mkfd and talus

coIIBction at the base of the cliffs as talus sIapes, Freeze-thaw shattering occurs at rn

abandoned plunge poolkolk inside the eastern mgin of the mouth, more than 250 m

away from CWS of the Ancient Lake catam$. The exposed bedrock is discontinuously

mantled by a layer angular to sub-angular rock fragments, 5 to 25 cm (intermdate

diameter) resembling colluvium and talus. The rock e n t s have a we&, < lmm

weathering rind, little lichen growth with some baving an evaporite coating fkom the

flooding of the cataract in the early 1950s. Similar weathering has formed a weII

developed weathering mantle on the long plateau surface of the interfluve, A k s

common form of physical weathering in the area is root wedging, the wedging apart of

rock by shrubs growing the joints of rock. Tbough this is not common in the study site, it

dms accur on cliff faces. Spalling occurs with isolated boulders creating a round

corestone. An example of spalling is found on the fosse side of the pendant bar dong the

south wall of the Ancient Lake c a m t measuring 0.75 m (Figure 20).

. .. ' .. I - . . I I " '

I

Figure 20. Oblique ground view of spalling, b d r corestune resting in fosse of pendant bar 1-ted on the swth side of the Ancient lake a&ract. Note the joinling paraltet to tbe surface on the rock creating a round corastone. Also note the red-brown weathe* rlrrd and white evaporite coating. (Seth Ma- for scale)

Chemical weathering: Chemical weathering is the in situ decomposition of rock via

chemical reactions resulting in the formation of new minerals. The dominant chemical

weathering in this area is oxidation; the process leads to the collapse of the crystal

structure of the. iron in the basalt enabling weathering by other means, Oxidation of iron

minerals is shown as a red weathering rind on exposed basalt be it a cliff or rock

fragment. The development of the oxidation weathering rind varies with the amount of

time the rock is exposed to the environment; thus a freshly broken piece of basalt will

show little or no weathering rind in contrast to a fragment of basalt with long exposure to

the environment will show a deeper weathering rind. The basalt rock fragments on the

interfluve have resulting from a combination of oxidation and chelation (chemical

weathering resulting from the production of organic acids by biota such as lichen). The

basalts are subject to hydrolysis, replacement of Potassium cation (0 with Hydrogen

ion 0 with the pmence of warn to break down the mineral to clay.

Comoodte W t x t k ~ As mentioned previously physical and chemical weathering

rmly mnr independent of each other, so the two will dso be addressed simd~6ously,

The long inkdive and cataract rim surf& exbibit signs of composite chemical and

physical weahring o c c ~ g together in a feedback system. During the f o d a n of

the Potholes Coulee and subsequent floods, the surface was stripped of available

sediment* leaving the W k bare. After thh time physical and chemical weathering

ocamd W g a &&ow weathering mantle. A combination of frost action, freeze-

thaw Euad oxidation fragmented rock on the surface d n g more surface area enabling

chemical watherhg, The rock fragment were then subjected to further physical and

chemical weahring decomposing and degradhg the rock frsrgment into angular to sub-

angular very coarse oxidized basalt sand and pebbles (figure 21). Tbe composite

weathering regime on the interfluve has culminated in forming a shallow, well-developed

weathering prome capped by loess. The stability and location of the sediment has

enabled various biota and landforms to form such as patterned ground resulting fmm

shrink-swell and lichen.

~ r e 2 ~ ~ a n d ~ w e n U & & g w t h e ~ e ~ Notetbebasaltweatheredto p a g a i a r ~ a f f l ~ - ~ & , a n d p e b b h t h e m ~ r f n d , a n d b b ~ ~

Eolian Demsition

Eolian proeesscs in past and present affected the landscape with loess and cover

sand blmketing the flwial depositions and weathering mantles. The loess forms as very

fine sediments mmported as mspded bad then settles from the air in areas of

decreased velocity and is tbe dominate land cover within the Columbia Basin. The depth

of loess ranges from 20 cm at the mouths d rims ~f the cataracts to more then 1 .S rn on

striped bedrock terraces, damct flm, and dong the cliff bases of Babcock Bench, The

loess consists of buff colored silt-sized particles and varies in compaction thoughout the

year based on available moistwe and bioturbation. A thin, discontinuous cover-sandnag

resulting from deflation is found thmugh out the study site, mostly occurring at the mouth

of the catam& dong Babcock Bench or areas of consistent bioturbation. Eolian

processes still occur, deflating disturbed surfaces as well as depositing loess.

M a s Wasting Features

Mass wasting is the dowaslope movement of sediment andfor bedrock as a result

of gravity and is affected by fluvial undercutting, weatking, slope, aspect, climate, and

vegetation. Mass wasting occurs in the study site as tskFa& Wand slides,

undifferentiated slides and wlifluction ranging in magnitude of events from s d

rockfall (<I 0 cm) to composite undifferentiated landslides more than 500 m wide.

Rockfall: Rockfall rxcurs when a rock is pulled h m a vertical. or newly vertical surface

by gravity enabled by frost wedging and Ereeze-thaw action. Rockfall in the area occm

at d aspects of expasure with the most occurring along cliffs with a northern aspect and

ranges h n 3cm to >5 m in diameter. For this report, roclcfrtll is classified as two

categories baed on s i z talus and discrete large block

Tdus is class5ed in this report as coarse angular rock fragments, less than 1 m

intermediate diameter, that collects at the base of the cliff it fell from The majority of

the &all is classified as talus and forms 20'-30" slopes, more than 25 m tall: The

majority of the chsts, in talus, mge h m 5 - 50 cm diameter with some cIasts up to 1 m

in diamter. The talus c o w coaIesce into one continuous apron at the bases of the cliffs

in the study area, partially to completdy £ilhg the fosse side of the bars. The talus

slopes show no pressure ridges or a pronounced be= at the toe of the slope @gure 22).

M- 22. Oblique p o n d view of talm s lop mdtling fasse dde of crewmtlpht bar s o d of Potholes Codee on Babeaek Bench.

Discrete large black rocHall is classified as angular blocks of rock that collects at

the base of the cliff it fe11 from occurring as large blocks greater than 1 meter

intermediate diameter and as Iarge as 10 meters intermediate diameter. It consists of

entablature or colonnades that succumb to the forces of gravity enabled by the jointed

nature of the bastsalt bedrock, physical weathering, seismic events and sometimes extreme

weather. In the study site, rockfall commonly occurs from cliffs with a northern aspect in

both the Ancient Lake cataract and the Dusty Lake cataract as we11 as the along the

Babcock Bench (Figure 23). Much of the large bIock rockfall, after rolling, comes to rest

mantling the fosse side of bars and the cataract floors. :' ' .*IF, Lf.7 - ' ': 1 ;

Figure 23. Oblique pd view of large bloc% rock M on B h o c k Ben&. TbiF rock is more than 5 meters in intermdate diameter.

Landslides: Landslides result from the downslope sliding of an area or the slope pulled by

gravity enabled by bedrock structure, fluvial undercutting, weathering, seismic events, ox

extreme weather. Landslides occurring at the study site incIude rotational slides and

undifferentiated slides and range in width from 50 m to greater than 300 ra. The

landslides occur on slopes with northern aspects in Ancient Lake, and Dusty Lake

cataracts; and western aspects along the slope between the Babcock-Evergreen Ridge and

Babcock Bench.

Rotational landslides are mass movements in which the bottom of the slope is

cantilevered away from the slope allowing the top of the slope rotated downslope leaving

a scallop-shaped scarp in the cliff above the slide. The morphology of a rotational

landslide includes: a sag, hallow, depression like W, behiud the main body with a toe

at the: terminus of the slide. Rotational slides in the study site are often easily identified

by the offset of the once vertical colonnade after the slide has corn to rest. A textbook

xample of a bedrock rotational slide ~~ in middle of the south side of the Ancient

A e cataract (Figure 24). The slide d after bar deposition as it and asso~htd

lebris rest on the fosse side. of a pendant bar.

Und8fprentiate.d lrtndslides are landslides that the mechanics offbe slide cannot

le determined by visual, ohat ions dtber due to the nature of the slide or past event

nod i f i don . These landslides o m in the southwest extent of the study site on the

Babcock Bench along the Evergreen Ridge south of the mouth of the Dusty Lake

cataract. The slides we recopkd by the scallop-shaped scarp left in the Evergreen ridge

above the slide. The diff~culty in determining the mechanism of the slide is that the main

body of the siide has been reworked by h e Pleis-ne flooding down the Columbia

fiver coupled with bar building. Two of the scarps have channels leading to them

indicating fluvial flow prior or subsequent to tbe mass wasting event. Two hn south of

the cmca-point bar is an undiEerentiated lmdsfide with the scarp width greater than

Solifluction: Solifluction h the down dope movement of a subs-, in this case flood

gavels on a bar, by graw enabled by saturation ofthe substme. Sulifluction cmmd

on the channel side of the pendant bar dong the north waIl in the head of the Ancient

M e cataract, The movement occnrred on a slope than 20 degrees providing ttae

energy necessary to compellsate for the weIJ drahhg rmbstrab of ahe bar. The feature is

10 m wide 20 m long and 0.5 m deep with a small tm on the down slope side of the

Reatwe.

Biotic Geonmmhic Fbatws

Bafa (flora, faun& and htmm) can be compet%nt pmphic agents. The study

site has wikgom change by £bra, fa- and humans discreetly and in composite,

brirrging various forms of change. Biota can act as ether a slrrface stabilizer or a source

of &ace disruption.

Flora: A well developed flora egime indicates a stable surface. Grasses and shrubs

stab& the surface by covering the mufpbce making it resistant to eolian and slup

erosion. Lichen acts as a chemical weathexing geomorphic agent by secreting organic

acids that decompose the minerals of the rock it's growing on, thereby enabling other

forms of weathering and erosion. Lichen grows at a slow rate and the presence of well

developed lichen indicates a long duntion of surface stability.

F a u x Coyotes, badgers, mice and oher small mammolIs canse biohvbation of the

suffwe and subsurface mixing the stratum of the sail pmfde by burrowing and fomghg.

Worms chum the soil as they work their way through creating a homogenous soil profile

;as well as adding h u m to the sail, Eoms and deer create trails and disrupt the surface

as they walk, enable and prepare the substrate for eolian processes (transportlde:£Mion)

and slope erosion. This is especially noticeable during transition from winter to spring

w h e ~ surface &grades from a compact surface to an uncolasolidated hose dust that

billows mmd ones feet.

flumans - Humans, though in the area for a short time, have been very effective

geomrphic agents. Humans have occupied the area for several thousand years prior to

modern upa at ion which began in early 1920s with homeskdng, The land use

includad range land tellring advantage of the natural corrals created by the atamcts

(personal communication, Dave Bishop, June 2002). The m a was without irrigation

save one pmdd spring on Babcock Bmch outside of tbe Potholes Coulee. In the

1950s the Cp1mnbia Basin higation Project brought w a r to the region for @cultme.

In the early 1950's, the Aneient Lake Cataract was flooded intentionally to create a lake,

however, due to a fault in the cataract the water slowly leaked out (Grolier 1965). There

were sevrerd attempts to maintain the lake's level, however, this was abandoned in

subsequent yews. Despite the ephemeral, nature of this lake, it had an impact on the

cataract mating m c i d biotic barriers and creating new landforms. SaIts precipitated

from the ponded lake water, Ieaving an evaporite. The shomline mated a barrier

blocking the native flora that once occupied the area from re-inhabiting the area (Figure

261, Bacteria and more alkali tolerate plants could prwes the salts in the soil enabling re-

colonization by the local shntbs. kt present, more than 40 yeas since the lake was

abaudoned, a few sagebrush shrubs are beginning to occupy the area. The daminant flora

is cheat grass and Russian thistle.

The Iake did nat only impact the local biota, it also mat4 unique landforms.

The lake left temwfks and a %bat tub" ring of evapi te indicating the past sho~line

17,20, & 26). The tewacettes are continuous p d e l small terrace features

similar to shorelineg that can be fouod along resavois shores at present. It is unlikely

that they are of a faunal o m (cattle &.ail temttes), m they do not braid hga one

another. Also, the p h e n o ~ n e m be observed at modern memoirs.

is:

a 0 500 1000

Figure 26: 1962 US.D.A. airphoto of tbe Pothole8 showing waning lake waters m the Ancient Lake cataract. Note the wbite evapite deposition showing d m u m lake Ievet.

The Potholes Coulee has been affected by volcanism, kctonism, fluvial, eolian,

weathering, mass wasting, humans, and biotic geomorphic factors from the Miocene

epwh to present creating the Potholes Coulee, an amazing landform The Miocene-

Pliocene CaBGs created unique m k tbat was folded by Pliocene tectonic forces,

setting the stage for future modification by Pleistocene catastrophic f l d g events.

Th~ugh the events setting the stage for future moMcation occurrsd over millions of

years, they culmin&e in it msmndo of glaci6fluvial processes which sculpted amazing

landforms in the stark CRBGs. Throughout tbe Pleistwene, episodic catastrophic

flooding even& operated as competent erosional forces, plucking basalt along structural

weaknesses crdng the Potholes Coulee, and then deposited mvid mega-Worms

flooring the excavated cataracts. Eolian deposition blanketed the bedforms, wdherhg

mantles, and mass wasting deposits. Rockfall detritus mantles the base of the catatact's

walls. The combined geomorphic pracesses create a unique landscap. Potholes Coulee

is a steep walled double horsedm cataract with sinuous elongate kolk takes above the

heads of the catam&. Lakes fill concentric elongate plunge pools a the base of the

cataract's W. Mega-bars and bedforms of flood sediment discontinuousiy floor the

cataracts. Tdus and landslides mafltle the steep cataract walls. Varied depths of loess

blanket tbBe flood ssdiments and flora has s t & W the surface. Anthropogenic agents

expbited the setting through itrigation and M e building events, as well as comtructing

trails and introducing exotic fauna (cattle and Modern hams) to the area.

After nearly a century of research, many questions main regarding the

geomorphblogy of the Quincy Basin, and specifically the Potholes Coulee: 1) The

George Gravels in the George Chamel mmecttd to Potholes Coulee imply it was

f o d hundreds of thousands of years prior to the late Pleistocene catastrophic floods.

D b t research addmsing the age of the gravels and linking them to the Potholes Coulee

would 'be a valwb1e project in explaining the genesis of the Channeled Scabland; 2)

Exploring the blks on the interfluve in the Poth01es Coulee would yield further

understanding in the temporal origin of the glacio-fluvial activity that flowed through the

study site as well as reconcile the dramatic difference in weathering between the elevated

interftuve surface and lower cataract surfaces; and 3) Quantifying the current dunes by

understanding the sub-loess topography would allow description of the current dunes and

calculation of flow through the cataract at time of origin.

A c k n o w ~ t s

Tbis research was made possible by the financial suppart of the Evolving Earth

Foundati~n. I acknowledge David Bishop for excavating the sloth remains, historic site

description, use of his personal library, allowing access to the site, and bring his

discovery to the scientific c~mrnunity. I acknowledge Steven Hacbnberger for

incorporating this work into his fmal report, access to his personal study site photos, and

permitting access to the sloth site. I acknowledge Karl LilIquist for his guidance through

out the project, assistance in the field, and pf-readhg earlier versions of tbis

manuscript. I appreciate Robert Hickey, for guidance with GIS technologies and for

proof-readiug earlier versions, and Seth Mattos, for assistance in the field

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Western R e g i d Climate Center, Quincy Is, Washington, http:fhtww.wrcc.dri.&cgi- bin/cmAIN .pI?wquin