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
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
- r- , y e - - - - - .;. - - , . . - \ < Id
,I,
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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