.-,(/

GEOLOGIC UNIT CONTACT

BEDROCK WELL DATA POINT

COUNTY BOUNDARY OR TOWN

MAJOR HIGHWAY

Interstate Route

US Route

State Route

TOWNSHIP BOUNDARY

RIVER OR STREAM

Description of Map Symbols

#

Scale 1:250,000

5 0 5 10 15 Miles

5 0 5 10 15 Kilometers

(if printed 36" x 40" format)

DIGITAL GEOLOGIC MAP OF IOWAPHASE 3 : NORTH - CENTRAL IOWA

Prepared by

Brian J. Witzke

Greg A. Ludvigson

Raymond R. AndersonBill J. Bunker

Energy and Geological Resources DivisionGeological Survey Bureau

May 2001

Produced under the STATEMAP program, in cooperation with theU.S. Geological Survey, Department of Interior, Supported by

Cooperative Agreement 00-HQAG-0075

Sean Greeney

Iowa Department of Natural ResourcesJeffrey R. Vonk

Director

ACKNOWLEDGEMENTSRecognized for direct contributions to the map’s production:

Iowa DNR Geological Survey BureauDonald L. Koch and Matt Goolsby,

Index Showing Area of Geologic Map

Universal Transverse Mercator Projection, UTM Zone 15, North American Datum 1927

Kdw

Pc

Msp

Ma

Mg

Mmp

Om

Ogp

Dc

Dw

Df

Dl

LEGENDDescriptions of Rock Units

Rock Exposures in the Study Area

BUTLER

FLOYD

WRIGHT

HARDIN GRUNDY

FRANKLIN

HANCOCK

WORTH

HAMILTON

MITCHELL

CERRO GORDO

WINNEBAGO

Areas of bedrock exposure or bedrock surface within the soil horizon.

CRETACEOUS

Dakota and Windrow fms.; mid Cretaceous (upper Albian and/or Cenomanian); interval generally includedin Dakota Fm. across western map area, outliers in eastern map area generally assigned to Windrow Fm.Maximum thickness 150 ft (46 m) in Wright and Hancock counties. Primary lithologies: sandstone, partpebbly to conglomeratic , part cemented by iron oxides; mudstone, pale to medium gray, red. Secondarylithologies: chert residuum/gravel; siderite pellets .

P ENNSYLVANIAN

Cherokee Group undi fferentiated; Middle Pennsylvanian (Atokan-Desmoinesian). Maximum thickness:170 ft (52 m) in Hardin Co.; infilling of irregular erosional surface produces locally variable thickness.P rimary lithologies: shale, medium to dark gray, part sandy; sandstone, vf-c. Secondary lithologies: shale,black, carbonaceous; s iltstone; coal; underclay, pale gray. Minor: pebbly sandstone; shale, red to pale gray;s iderite concretions; limestone; pyrite.

M ISSISSIP PIAN

“St. Louis” and Pella fms.; Middle Mississippian (Meramecian). Maximum thickness 60 ft (18 m) inHamilton Co. P rimary lithologies: dolomite, part sandy; sandstone, part dolomitic; green-gray shale.Secondary lithologies: limestone, part sandy to sublithographic; breccia. Minor: oolitic limestone, chert.

Augusta Group, includes “Keokuk” and “Warsaw” fms.; Middle Mississippian (Osagean). Maximumthickness 85 ft (26 m); locally truncated beneath sub-“St. Louis” unconformity. Primary lithologies:dolomite, part argillaceous; dolomitic limestone; Secondary lithologies: green-gray shale; limestone, skeletalto sublithographic; glauconitic dolomite or limestone; breccia. Minor: chert, chalcedony and quartz; ooliticlimestone, phosphatic dolomite.

Gilmore City Fm., includes Marble Valley, Humboldt, and Iowa Falls mbrs.; Lower Mississippian(uppermost Kinderhookian, lower Osagean). Maximum thickness 170 ft (52 m) in Hamilton-Wrightcounties; thins southeastward, 50 ft (15 m) in southeast Hardin Co. Primary lithologies: limestone, skeletaland peloidal packstone-grainstone; limestone, oolitic to coated-grain; dolomite (Iowa Falls facies).Secondary lithologies: oncolitic, intraclastic , and sublithographic limestone; dolomitic limestone.

Maynes Creek and Prospect Hill fms., locally includes Chapin and Eagle City members within MaynesCreek interval; Lower Mississippian (Kinderhookian). Maximum total thickness 165 ft (50 m) in Hamilton-Wright counties, thins southeastward, 65 ft (20 m) in southeast Hardin Co.; maximum Maynes Creek Fm. 155ft (47 m); Chapin Fm 0-10 ft (3 m); maximum Prospect Hill Fm. 30 ft (9 m) in Franklin Co., elsewheregenerally <10 ft (3 m). Primary lithology: dolomite, part cherty to very cherty. Secondary lithologies:skeletal, oolitic , and sublithographic limestone; dolomitic limestone; silts tone (Prospect Hill). Minor: shale(Prospect Hill).

DEVONIAN

Famennian interval , includes upper shale (“Maple Mill”), Aplington Dolomite, Sheffield Shale; UpperDevonian (Famennian). Maximum thickness 150 ft (45 m) in Hardin Co., thins westward to 40 ft (12 m);Aplington Dolo.. locally to 50 ft (15 m). Primary lithologies: shale, green/olive-gray to gray, silty; dolomite,part argillaceous to s ilty, part cherty/siliceous. Minor: siltstone; oolitic ironstone (upper part), pyrite.

Lime Creek Fm., includes Juniper Hill, Cerro Gordo, and O wen members in eastern map area,undifferentiated to west; Upper Devonian (upper Frasnian). Maximum thickness 160 ft (49 m). Primarylithologies: shale, green-gray to gray, silty, calcareous; dolomite, part argillaceous (dolomite-dominated towest). Secondary lithologies: limestone, fossiliferous, part argillaceous. Minor: oolitic limestone, pyrite.

Cedar Valley Group; Shell Rock, Lithograph City, Coralville, Little Cedar fms.; Middle to Upper Devonian(upper Givetian-lower Frasnian). Maximum thickness 350 ft (107 m); truncated and overstepped westward inWinnebago Co.; maximum Little Cedar (Bassett, Chickasaw, Eagle Center, Hinkle mbrs.) 110 ft (34 m);maximum Coralville (Gizzard Creek, Iowa City mbrs.) 80 ft (24 m); maximum Lithograph City (OsageSprings, Idlewild mbrs .) 100 ft (30 m), maximum Shell Rock (Mason City, Rock Grove, Nora mbrs.) 75 ft(23 m). Primary lithologies: dolomite, fossil-moldic to vuggy; limestone, variably dolomitic, fossiliferous tosublithographic, part argillaceous. Secondary lithology: gray to green-gray shale, dolomitic. Minor:glauconitic dolomite; sandy dolomite or limestone; chert.

Wapsipinicon G roup; Pinicon Ridge, Spillville fms; Middle Devonian (upper Eifelian-lower Givetian);forms bedrock surface only in small areas of Floyd-Mitchell counties. Maximum thickness total interval: 130ft (40 m); maximum Spillville 90 ft (27 m); maximum Pinicon Ridge (Kenwood, Spring Grove-Davenportmbs.) 42 ft (13 m). Primary lithologies: dolomite, fossil-moldic to vuggy; dolomite, laminated or sandy;limestone, dense to sublithographic, partly to wholly brecciated. Secondary lithologies: shale, dolomitic tosandy. Minor: chert and chalcedony; sandstone.

ORDOVICIAN

Maquoketa Fm., Elgin Mbr.; Upper Ordovician (Richmondian), forms bedrock surface only in WinnebagoCo. Maximum thickness: 95 ft (29 m). Primary lithology: dolomite, part cherty to very cherty. Secondarylithology: limestone, fossiliferous, part cherty. Minor: shale.

G alena Group, includes Dubuque, Wise Lake, Dunleith, Decorah fms.; Upper Ordovician (Chatfieldian-Maysvillian); forms bedrock surface only in Winnebago Co. Maximum thickness 285 ft (87 m). Primarylithologies: limestone, part dolomitic; dolomite. Secondary lithologies: cherty limestone; cherty dolomite;green-gray shale, calcareous.

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Pc

Ma

Kdw

Kdw

Kdw

Mmp

Pc

Ma

PcMsp

Kdw

Kdw

Dl

Kdw

Dc

Kdw

Dl

Pc

Pc

Dl

Kdw

Pc

Kdw

Df

Dl

Msp

Pc

Pc

Mg

Pc

Pc

Kdw

Pc

Df

Ma

Pc

Kdw

Ma

Pc

Df

Kdw

Mmp

Kdw

Df

Pc

Dl

Kdw

Pc

Df

Kdw

Pc

Pc

KdW

Pc

Df

Kdw

Ma

Kdw

Df

Kdw

Pc

Mg

Kdw

Kdw

Df

Ma

Kdw

Kdw

Ma

Kdw

Pc

Kdw

Kdw

Dc

Kdw

Msp

Kdw

Kdw

Pc

Kdw

Kdw

Msp

Mmp

Ma

Kdw

Mg

Dl

Kdw

Pc

PcMa

Kdw

Msp

Dl

Msp

Pc

Kdw

Df

Kdw

Kdw

Dl

Pc

Ma

Dc

Df

Mmp

Msp

Kdw

Ma

Kdw

Ma

Kdw

Msp

Pc

Kdw

Df

Df

Pc

Pc

Kdw

Pc

Kdw

Kdw

Pc

Df

Pc

Df

Dl

Mmp

Msp

Pc

Pc

Dl

Msp

Mmp

Mg

Pc

Mg

Kdw

Mg

Kdw

Mg

Ma

KdwKdw

Pc

Pc

Dl

Pc

Dl

Mg

Pc

Dl

Ma

Kdw

Ma

Pc

Msp

Kdw

Msp

Df

Pc

Pc

Msp

Ma

Ma

Kdw

DlDl

Kdw

Mg

Df

Kdw

Kdw

Df

Ma

Kdw

Kdw

Pc

DlDl

Dl

Kdw

Mmp

Dl

Kdw

Ma

Ma

Msp

Kdw

Mmp

Kdw

DlDl

Dl

Dl

Pc

Kdw

Dl

Kdw

Dl

Msp

Dl

Ma

Dl

Ma

Kdw

Kdw

Kdw

Dl

Kdw

Kdw

Kdw

Kdw

Msp

Kdw

Kdw

Kdw

Kdw

Kdw

Dl

Mmp

Dl

Dl

Dl

Mmp

Kdw

Om

Ogp

Ogp

Om

Dw

Dw

Kdw

Dl

Dl

Kdw

Dc

Dc

DcDc

Dc

Dc

Dc

Dc

Dc

Dc

Kdw

Ma

Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg

Mg

MspMsp

Msp

Ma

Mg

Mg

Msp

Msp

Msp

Msp

Msp MspMsp

Pc

Pc

Pc

Pc

Pc

Pc

Pc

Pc Pc

Pc

Pc

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Pc

Pc

PcPc

Pc

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Msp

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Ma

Ma

Ma

Ma

Ma

Ma

Mg

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Mg

Mg

Mg

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Mg

Mg

Mg

Mg

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Mg

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Mmp

Mmp

Mmp

Mmp

Mmp

Mmp

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Pc

Pc

Pc

Pc

Pc

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Df

Df Df

DfDf

Df

Df

Df

Mg

MgMg

Df

Df

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Mmp

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Dl

Dl

Dl

Dl

Dl

Dl

Dl

Dl

Dl

Dl Dl

Dl

Dl

Dl

Df

Df

Df

Df

Df

Df

Dc

Dc

Dc

DcDc

Dc

Dc

Dc

Dc

Dc

DcDc

Dc

Dc

Dc

Dc

Dc

Dc

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Ma

Ma

Df

DfDf

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Df

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Dl

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Dl

Dl

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Dl

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Dl

Dl

Dl

Dl

Dl

DlDl

Dl

Dl

Dl

Dl

Dl

Dl

Df

Df

Dl

Dl

Dl

Dl

Dl

Little Buffalo Creek

Dc

Ma

Ma

Clear Lake

Upper Pine

Lower Pine

Kdw

Mmp

Mmp

Kdw

Mg

Pc

Kdw

Mg

Mg

Mmp

Mmp

Mmp

Dl

Mmp

DfDf

Df

Df

Dc

Win

neba

go R

iver

Win

neba

go R

iver

Winn

ebag

o Rive

r

Winnebago River

Shell Rock River

Elk Creek

Cedar River

Cedar River

Little Cedar River

Wapsipinicon R

iver

Littl

e C

edar

Riv

er

Little Cedar River

Cedar River

Floyd Creek

Shell Rock River

Winnebago River

Wes

t Bra

nch

Iowa RiverE

ast Branch

Boone River

Iowa River

West Branch

Iowa R

iver

Boone

Rive

r

West Branch

Iowa River

Iowa River

Whit

e Fo

x Cre

ek

Cedar River

West Fork

Cedar River

West Fork

Floyd Creek

Shell Rock River

Shell Rock River

Beaver Creek

Beaver Creek

Beaver Creek

Blackhawk Creek

Lake

Lake

Iowa River

South Fork

Honey Creek

Iowa River

Sku

nk R

iver

Boone River

Boone

Rive

r

Pc

Pc

Pc

Dl

Mmp

Mmp

Kdw

Dc

Dc

Dc

Dc

Dc

Pc

Dc

Beeds Lake

93 30'o

93 30'o 93 00'o

o93 00'R26W R25W R24W R23W R22W R21W R20W R19W R18W R17W R16W R15W

R26W R25W R24W R23W R22W R21W R20W R19W R18W R17W

R16W R15W

T100N

T99N

T98N

T97N

T96N

T95N

T94N

T93N

T92N

T91N

T90N

T89N

T88N

T87N

T86N

T100N

T99N

T98N

T97N

T96N

T95N

T94N

T93N

T92N

T91N

T90N

T89N

T88N

T87N

T86N

43 00'o

o42 30'

43 30'o43 30'o

43 00'o

42 30'o

.-,35

.-,35

.-,35

.-,35

(/69

(/69

(/69

(/69

(/69

(/65

(/65

(/65

(/65

(/65

(/218

(/218

(/218

(/218

(/18

(/18

(/18(/18

(/18

(/18

(/20

(/20

(/20

(/20

(/20(/20(/20

14

14

14

14

14

9

9

9

9

214

147

107

107

188

3333

57

17

17

175

175

175

175

175

359

214

299

Prepared by the Iowa Department of Natural Resources,Geological Survey Bureau, May 2001.

Open File Map 01-3