Notes to accompany 2018 Friends of the Pleistocene, Paci�c Northwest Cell, Sept. 7-9, 2018:

Northwest Channeled Scablands (and other related topics) Leaders:Jim E. O’ConnorRichard B.WaittVictor R. BakerAndrea M. BalbasJon RiedelIsaac LarsenKarin Lehnigk assisted by JoJo Mangano

DarogaState Park

1

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OkanoganRiver

C l a r kF

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B i t t e r oo t

Ran ge

WillametteValley

C o n t i n en

t a l

D i v i de

Purcell Trench

MosesCoulee Gran

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Cou

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Methow R.

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Col

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2

Northwest Channeled Scablands; Supplemental Trip Notes Pacific Northwest Cell, Friends of the Pleistocene Sept. 7-9, 2018 Prepared by Jim O’Connor The Channeled Scabland: Decimated to desperately low numbers by the huge megafloods ripping through the Pacific Northwest, late Pleistocene megafauna marked coulee pathways between far-flung remnant populations on each other’s hides. The scabbed markings, noted by first hunters, were the source of the descriptive term Channeled Scablands. Well, that’s not completely true, but we can pretty much say anything since this ‘guide’ has not undergone USGS review and is not approved for publication, distribution or citation.

Agenda:

Day 1: The Columbia and lower Chelan Valleys—floods, glaciers, outwash, lakes, and floods

Day 2: The Columbia diverted—Grand Coulee, Moses Coulee

Day 3: Convergence

Besides these supplementary notes and maps, directly relevant trip materials include (all available by ftp site): 1. Informal guide for this trip prepared by Jon Riedel. Applicable to stops 1.2 and 1.4. file: FOP2018_Chelan_Stops_1.2_1.4_Jon_Riedel.pdf. 2. Informal materials for this trip prepared by Karin Lehnigk and Isaac Larsen. Applicable to stops 2.3 and 2.6. file: FOP2018_MosesCoulee_Stops_2.3_2.6_UMass.pdf. 3. Guide prepared for 2017 GSA trip by Richard Waitt, includes many stops for this trip:

Waitt, R. B., 2017, Pleistocene glaciers, lakes, and floods in north-central Washington State, in Haugerud, R.A., and Kelsey, H.M., eds., From the Puget Lowland to East of the Cascade Range: Geologic Excursions in the Pacific Northwest: Geological Society of America Field Guide 49, p. 175–205, doi:10.1130/2017.0049(08). 4. Guide prepared Vic Baker et al. for 2016 GSA field trip; includes many stops for this trip:

Baker, V.R., Bjornstad, B.N., Gaylord, D.R., Smith, G.A., Meyer, S.E., Alho, P., Breckenridge, R.M., Sweeney, M.R., and Zreda, M., 2016, Pleistocene megaflood landscapes of the Channeled Scabland, in Lewis, R.S., and Schmidt, K.L., eds., Exploring the Geology of the Inland Northwest: Geological Society of America Field Guide 41, p. 1–73, doi:10.1130/2016.0041(01). 5. Geology article by Andrea Balbas et al. reporting recent cosmogenic dating in region

Balbas, A.M., Barth, A.M., Clark, P.U., Clark, J., Caffee, M., O’Connor, J.E., Baker, V.R., Konrad, K., and Bjornstad, B., 2017, 10Be dating of late Pleistocene megafloods and Cordilleran Ice Sheet retreat in northwestern United States: Geology, v. 45, p. 583–586; doi:10.1130/G38956.1; includes GSA Data Repository item 2017193. 6. Nature article on Moses Coulee erosion by Larsen and Lamb

Larsen, I.J., and Lamb, M.P., 2016, Progressive incision of the Channeled Scablands by outburst floods: Nature, v. 538, p. 229–232m; doi:10.1038/nature19817. 7. A kmz file of stop locations: FOP2018PNW_Stops.kmz

3

Figure S1: 10Be surface exposure ages of boulders and bedrock from sites 1-14 (Figure 1, Figures S2-S49, Tables S1, S2). Individual samples are defined on the x-axis with sample age and 1 σuncertainty on the y-axis. Site numbers appear in the upper left corner of each plot (Figure 1). Circles represent flood deposited boulders except for Northrup Canyon, which is bedrock; squares represent glacier erratics; diamonds represent ice-rafted boulders. Purcell Trench data (site 4) are from18. Individual site ages and uncertainty are shown in the right bottom corners. All errors are reported at 1σ and include the uncertainty in the 10Be production rate used (4.8%). The * represents an error-weighted mean and uncertainty, † indicates a site mean and standard error, and ◊represents the analytical external error on the single sample.

From Balbas et al. (2017) 1.2

1.2

1.6

2.5

2.3

3.1

Stop Number

4

Maxim

um LGM Okanogan Ice Lobe

Lake Chelan

Wenatchee

Oka

noga

n Ri

ver

Methow River

2.1

1.6

1.5

Colu

mbi

a Ri

ver

Columbia River

1.1

Daroga State Park

1.2

3.14.4

4.5G

rand

Coulee

Moses Coulee

Waterville Plateau

Quincy Basin

Potholes Coulee

Lynch Coulee

Frenchman Coulee

2.2

2.3

2.42.5

2.6

3.2

3.3

0 25 50 kmDEM courtesy of Ralph Haugerud

1.3,4

OmakPlateau

5

Location,directions,andnotes Lat. Long. TotalMileage

IncrementalMileage

Doraga State Park, Group Campsite G‐2 47.70135 ‐120.194865 0 0

North (left) on Highway 97 0.1 0.1

Right on Brays Landing Road, ascend giant flood bar 1.5 1.4

Eolian dunes to the right, giant current dunes to left 2.5 1

Crossing giant current dunes 3.5 1

Right on Singleton Road 5.3 1.8

Stop 1.1; Brays Landing view, at jct with Higgins Loop at crest of 

hill; overview of Columbia Valley; down‐Columbia floods, Great 

Terrace.

47.752967 ‐120.150571 5.6 0.3

Turn around, descending Singleton Road 5.6 0

Right on Brays Landing Road 5.9 0.3

Onto Great Terrace, here perhaps flood scoured by glacial Lake  6.7 0.8

Right on US 97 (northbound) 6.9 0.2

Nice view of Great Terrace ascending upstream 7.7 0.8

Approximate downvalley limit of Okanogan lobe 11.3 3.6

Beebe Bridge crossing of Columbia River 17.7 6.4

Left onto WA 150 (toward Chelan) 18 0.3

Gneiss of Chelan complex 18.7 0.7

Gravel fill plugging pre‐LGM outlet of Lake Chelan 19.1 0.4

Left on Alt 97 toward Chelan 21 1.9

Right on Bradley St. (School zone) 21.7 0.7

Chelan Rustler's rodeo ground on one of many kame surfaces 22.7 1

Left onto Union Valley Rd. 23.6 0.9

Park outside gate for Stop 1.2 47.86246  ‐120.018563 23.9 0.3

Stop 1.2; Union Valley moraine (walk up) 47.858586 ‐120.023606 ‐23.9

Stop 1.2 parking; Turn around and head back down Union Valley  23.9 23.9

Right on Bradley St. (School zone) 24.2 0.3

Right on East Johnson Ave. 26 1.8

Left on Sanders St. 26.1 0.1

Right on Trow (after crossing E. Woodin Ave.) 26.3 0.2

Stop 1.3; Lunch at Chelan Riverwalk Park 47.839161 ‐120.01825 26.6 0.3

Turn around, heading east on E.Trow Ave.; crossing Sanders St. 26.8 0.2

Right on Robinson St. 27.1 0.3

Stop 1.4; Chelan Ballpark gravel parking area; view of drift 

stratigraphy

47.83628 ‐120.00857 27.5 0.4

North on Robinson, turn right on Woodin Ave. 27.7 0.2

Straight onto Alt US 97 27.9 0.2

Descend off Howard Flats, a recessional outwash terrace (capped 

by eolian dune, overlies lacustrine?)

30.8 2.9

Left (north) onto US 97 32.7 1.9

Wells Dam 38.8 6.1

Right onto Starr Road 41.9 3.1

On boulder bar 44.2 2.3

Stop 1.5; Pateros boulder bar; glacial Lake Columbia outburst 

flood bar

48.036339 ‐119.89162 45.4 1.2

Right onto US 97 (northbound) 45.6 0.2

Methow River 46.3 0.7

Pateros 46.7 0.4

Enter Brewster 53 6.3

Turn right for "Heritage Marker" (brown sign) 56.4 3.4

Left at T  56.4 0

Stop 1.6; Fort Okanogan; Okanogan River view, site of Columbia 

River blockage

48.10236 ‐119.72187 56.6 0.2

Back to US 97, turn left (south) 56.7 0.1

Stay south on US 97 80.1 23.4

Beebe Bridge across the Columbia 85.3 5.2

Daroga State Park; Group Camp 2G 47.70135 ‐120.194865 101.5 16.2

Day 1; The Columbia (and Chelan)

6

495

490

120°10'0"W

120°10'0"W

0 0.35 0.7 1.05 1.40.175Miles

0 0.35 0.7 1.05 1.40.175Kilometers

Bray’s Landing Area

1.1

Navarre Coulee Knapp Coulee

Columbia River

Loess-covered CRBG

Scabland

Missoula Flood barscovered with Current Dunes

Outwash te

rraces, max Okanogan lobe

Glacial Lake Columbia Outburst Bar

Eolian Dunes

7

ChelanLake Chelan

1.2

Union Valley Moraine Area; Stop 1.2

8

Chelan River Area

Chelan Butte

Moraines

Chelan

1.4

Dam

Pre LGM outlet

HoloceneBedrockIncision

9

1.5

1.6

Approximate�nal rock-controlled

level of glacialLake Columbia

(1530’ ft; 465 m)

Okanogan Confluence Area

Waterville Plateau

Columbia River

Col um

bia R

iver

Oka

noga

n Ri

ver

Methow Riv.

10

Location,directions,andnotes Lat. Long. TotalMileage

IncrementalMileage

Doraga State Park, Group Campsite G‐2 47.70135 ‐120.194865 0 0

North (left) on Highway 97 0.1 0.1

Right on McNeil Canyon Rd NW (just before Beebe Bridge 15.8 15.7

Gravel pit below exposes stratified recessional outwash gravel 18 2.2

Basalt haystacks glacially carried from rim basalt 20.4 2.4

Exit glaciated area 21.8 1.4

Contact between gneiss and Columbia River Basalt Group, locally 

marked by sedimentary interbeds

22.3 0.5

Back into glaciated terrain, signalled by basalt haystacks 22.6 0.3

Drift over basalt 23 0.4

Right on F Road NW 23.8 0.8

U‐turn at quarry, park on road shoulder heading east 24.4 0.6

Stop 2.1; Withrow Moraine (on crest of hill) 47.83001 ‐119.87188 24.5 0.1

Right toward Mansfield 24.8 0.3

Lone Butte view 31.5 6.7

Bend right into Mansfield (main street) 36.1 4.6

Left, following 172 toward Grand Coulee (City Park and restrooms 

across street and to right)

36.5 0.4

Yeager Rock 40.5 4

Pot Hills; an ice‐transported section of basalt flow 44.6 4.1

Left (north) on WA 17; dropping into Foster Coulee 49.5 4.9

Gravelly esker complex 50.7 1.2

Right onto 174 East 57.1 6.4

Begin descent into Columbia River valley 74.3 17.2

Left toward Crown Point Vista 76.8 2.5

Stop 2.2; Crown Point Vista; eastern extent of Okanogan lobe 

blockage, glacial Lake Columbia terraces, entrance to Grand Coulee, 

Grand Coulee Dam

47.9715 ‐118.98584 78.1 1.3

Left onto 174 East 79.5 1.4

Enter town of Grand Coulee 80.6 1.1

Right on 155 South toward Coulee City 81.4 0.8

Granite knob on left site of 17.2±2.7 ka 36Cl exposure age 

(Keszthelyi et al., 2009)

81.9 0.5

Lake sediments; isostatically uplifted ~20 m 84.8 2.9

Right into Northrup Point boat ramp area 88.3 3.5

Stop 2.3; Northrup Point, park in picnic area toward right 47.871386 ‐119.098207 88.8 0.5

Return and right onto 155 South (at entrance to Northrup Canyon 

cataract complex)

89.1 0.3

Coulee bottom boulder bar 96.6 7.5

Crossing bent basalt of Coulee Mononcline 105.8 9.2

Junction US2 (west) 108.1 2.3

Banks Lake outlet, controlling elevation for late stage glacial Lake 

Columbia (465‐470 m)

110.9 2.8

Left on 17 toward Ephrata 114.8 3.9

Left into Dry Falls State Park 114.7 ‐0.1

Stop 2.4 Dry Falls State Park 47.606885 ‐119.364244 114.8 0.1

Right onto 17  114.8 0

Left onto US 2 (Westbound) 116.8 2

Tilted basalt of Coulee Monocline, tracked by lower Grand Coulee 117.3 0.5

Glaciated Waterville Plateau 121.1 3.8

Descending into unglaciated Moses Coulee 132.3 11.2

Turn right up coulee toward Jameson Lake and Jack's Resort 133.7 1.4

Stop 2.5; Moses Coulee flood bar, moraine, and outwash view 47.64293 ‐119.67898 136.8 3.1

Return to US 2, turn right (west), at base of large flood bar 140.1 3.3

Left (south) on Moses Coulee Road 141.3 1.2

Eddy bar on right 146.3 5

Right onto 24NW (off of Sagebrush Flats Road) 152.7 6.4

Stop 2.6; Moses Coulee Rattlesnake Springs scabland 47.4369 ‐119.79988 157.8 5.1

Billingsly Ranch 158.2 0.4

Crossing Badger Mountain anticline 163.3 5.1

Palisades townsite 165.3 2

Bedded silt in stream‐ and road‐cuts are from Missoula floods 

backflooding up Columbia River from Quincy Basin outlets and 

inundating lower Moses Coulee

171.5 6.2

On expansive flood delta bar at mouth of Moses Coulee 176 4.5

Right onto 28 (north) 176.7 0.7

Rock Island Dam 180.1 3.4

Pangborn Bar view; perhaps largest Missoula flood bar 183.1 3

East Wenatchee; continue north on 28 191.3 8.2

End of 28 in East Wenatchee; continue north on US 97 (and US2) 195.4 4.1

Flood sculpted landslide mass of Turtle Rock in Columbia channel 202.3 6.9

Exposed Swakane biotite gneiss 211.8 9.5

Highway 2 turns east; stay on US 97 N 223.8 12

Doraga State Park, Group Campsite G‐2 47.70135 120.194865 241.6 17.8

Day 2; The Columbia diverted

11

Day 2; Stops 2.2 and 2.3

ExumedGranite

ExumedGranite

Banks Lake

Steamboat Rock(glaciated) Maximum flood level

= ~750 m (2450’)

Grand Coulee Dam

Stop 2.2Crown Point Vista

Northrup Canyon Map

Glaciated Basalt

Flooded Basalt

Key Elevations:Columbia River level at Grand Coulee; 290 m; 960 ftPresent Grand Coulee threshold at Coulee City; 470 m; 1540 ftProment “Nespalem silt” terrace; 510-530 m; 1680-1750 ftPlausible pre-cutting Grand Coulee threshold; about 680-730 m, 2200-2400 ftMaximum inundation level; about 750 m, 2450 ft

Upper Grand Coulee Area

Stop 2.3

12

Bretz, 193213

Glacial Lake ColumbiaSediment

Eddybar

ExumedGraniteExumed

Granite

ExumedGranite

ExumedGranite

NOR2

NOR3, 4Stop 2.4

Banks Lake

Northrup Canyon Setting

Lake Sediment

14

Upper Moses Coulee Area

Drift

Drift mantled basalt

Bouldery�ood bar

Outwash

OutwashOutwash

2.5

Flooded basalt

15

Rattlesnake Springs, Moses Coulee Area

2.6

Bruce Bjornstad Photograph16

Location,directions,andnotes Lat. Long. TotalMileage

IncrementalMileage

Doraga State Park, Group Campsite G‐2 47.70135 ‐120.194865 0 0

Right (south) onto US 97 0.1 0.1

US 2 junction; continue south on US 97 5.6 5.5

View of Tenas George eddy bar across river 10.2 4.6

Turn right at Eastmont to stay on US 97 and cross Columbia 17.9 7.7

Columbia River 18.6 0.7

Exit onto Alt 97 (north) 18.9 0.3

Right on Alt 97 toward Entiat 19.1 0.2

Rocky Reach Dam 23.4 4.3

View of Turtle Rock landslide mass in valley bottom 25.3 1.9

 ~0.2 mile north of milepost 207, carefully turn left across highway into truck storage 

area

26.5 1.2

Stop 3.1; Tenas George gravel pit (turn off highway into gravel area); Great Terrace 

stratigraphy, Columbia River impoundment, Glacial Lake Columbia outburst flood bar

47.568368 ‐120.262901 26.5 0

Right onto Alt 97 (south) 26.6 0.1

Rocky Reach Dam 27.7 1.1

Continue south on Alt 97  through traffic circle 34 6.3

Stay left toward East Wenatchee 33.8 ‐0.2

Turn right to head to East Wenatchee on US2 and 97  34.2 0.4

Cross Columbia River; stay right  34.8 0.6

Turn right on Wash. 28 toward East Wenatchee 35.7 0.9

Historic 9th St. Bridge nestled among huge boulders from glacial Lake Columbia outburst 39.3 3.6

Bear right to stay on Wash. 28 39.5 0.2

Stay right on Wash. 28 39.9 0.4

Huge Pangborn Bar on left (north); valley‐blocking Malaga landslide on right 44.8 4.9

Rock Island Dam (oldest on Columbia); Columbia enters Columbia River Basalt 44.8 0

~0.2 mile south of milepost 12, carefully turn left into old highway alignment 53.3 8.5

Stop 3.2; Old highway cut, north end of Moses Coulee delta bar; Moses coulee flood 

gravel; lacustrine deposits; rhythmites from Missoula floods backflooding up Columbia 

River valley

47.330417 ‐120.076887 53.4 0.1

Left onto Wash. 28 (east/south)  53.5 0.1

Moses Coulee enters on left 54.7 1.2

Climb onto a huge mixed lithology eddy bar; probably from down‐Columbia flood pre‐

dating Okanogan lobe blockage

61.2 6.5

Pass under railroad 62.3 1.1

Right onto Crescent Bar Road 62.6 0.3

Left on W8 NW 62.7 0.1

Road end 62.9 0.2

Stop 3.3; Lacy's West Bar view; West bar; Lynch Coulee delta bar 47.227628 ‐119.99939 62.9 0

End of trip

Day 3; Convergence

17

Moses Coulee mouth

Moses Coulee

Columbia River

3.2

18

West Bar

±

0 0.5 1 1.5 20.25Miles

0 0.5 1 1.5 20.25Kilometers

MosesCouleeDelta Bar(modi�ed)

Pre-Okanogan lobedown-Columbia �oodeddy bar

Glacial Lake Columbiaoutburst �ood bar

Later outburst �ood(?)Glacial Lake Kootenay?

Babcock Bench Scabland

3.3

Lynch

Coule

e

19