Surficial Geology of the Ridgeway (Iowa) 7.5' Quadrangle LEGEND 92°0'0"W 91°57'30"W 91°55'0"W 91°52'30"W CENOZOIC

Qpsr 43°22'30"N Qal Qal Qal Qpsr D Qps Qal QUATERNARY SYSTEM 43°22'30"N Qal Qpsr Qpsr Qal Om Om Qps Qwa2 Qps Qal Om Om Qal Qwa2 Om Qal Od Qps Od Qal Owd Qps Owd Qpsr Qpsr HUDSON EPISODE Om Owd Qpsr Qal - Alluvium (De Forest Formation-Undifferentiated) One to four meters (3 – 13 ft) of massive to weakly stratified, grayish brown to brown Qal Qal Qal loam, silt loam, clay loam, or loamy sand overlying less than three meters (10 ft) of poorly to moderately well sorted, massive to moderately Qwa2 Om Owd Qps Qal well stratified, coarse to fine feldspathic quartz sand, pebbly sand, and gravel and more than three meters (10 ft) of pre-Wisconsin or late Qpsr Om Qpsr Wisconsin Noah Creek Formation sand and gravel. Also includes colluvium derived from adjacent map units in stream valleys, on hillslopes, Owd Qpsr Qpsr Owd Qal Owd and in closed depressions. Seasonal high water table occurs in this map unit. Owd Qnw2 Od D Qal Qnw2 Qal D D Qal D Qnw2 Qnw2 Om Owd Od Qpsr Qpsr D Qnw2 D HUDSON AND WISCONSIN EPISODE Om D D Om Om DD Qpsr Odpg Owd D D Qps Od Qnw2 – Sand and Gravel (Noah Creek Formation) Two to eighteen meters (6.5-59 ft) of yellowish brown to gray, poorly to well sorted, Om Owd Qps D DD Qnw2 Qps D Qpsr massive to well stratified, coarse to fine feldspathic quartz sand, pebbly sand and gravel with few intervening layers of silty clay. Along many Qwa2 valleys a thin mantle of loess, reworked loess, or fine-grained alluvium (Qal) may be present. This unit includes silty colluvial deposits derived Qnw2 Om Qal Qwa2 Owd Qwa2 Qpsr Qnw2 from the adjacent map units. In places this unit is mantled with one to three meters of fine to medium, well sorted medium to fine sand derived D D Qpsr Qps D from wind reworking of the alluvium. This unit encompasses deposits that accumulated in low-relief stream valleys during the Wisconsin Qal Qpsr Od Qal Qwa2 Om Qal Episode and Hudson Episode. Seasonal high water table and some potential for flooding. Od Od Qpsr Owd Qps Qwa2 Om Om Owd Qps Owd Od WISCONSIN EPISODE Qps Qal Om Owd Qps - Loess (Peoria Formation— silt facies) Generally 2 m to 8 m (6 – 27 ft) of yellowish to grayish brown, massive, jointed noncalcareous Om Qpsr Qps Qps Qal Qnw2 grading downward to calcareous silt loam to silty clay loam. May be loamy near the boundary with the erosion surface. Overlies massive, fractured, loamy glacial till of the Pre-Illinoian Wolf Creek or Alburnett formations with or without intervening clayey Farmdale/Sangamon Om Qpsr Qps Qps Geosol. In most areas the Pre-Illinoian till is 1 m to 5 m (3 – 16 ft) thick, but may be up to 8 m (27 ft) thick locally. This mapping unit Qnw2 Qps Om Qps Qwa2 Om encompasses upland divides, ridge-tops and convex-side slopes. Well to somewhat poorly drained landscape. Qps Om Qnw2 D Qnw2 Om Qnw2 Owd Om Qwa2 Qpsr - Loess over bedrock (Peoria Formation— silt facies) Generally 2 to 8 m (6 – 27 ft) of yellowish to grayish brown, massive, jointed OwDd D Om D Owd Qpsr D Qpsr noncalcareous grading downward to calcareous silt loam to silty clay loam. Overlies bedrock units or colluvium. This mapping unit Owd Om Owd Qpsr Qal Qpsr encompasses upland divides, ridge-tops and convex side-slopes. Well to somewhat poorly drained landscape. Owd Owd Qnw2 Od Od Od Qnw2 Qal Qwa2 - Loamy and Sandy Sediment Shallow to Glacial Till (sediment associated with erosion surface) One to three meters (3 – 10 ft) of Qal Owd Qwa2 Qnw2 Om Om Qpsr yellowish brown to gray, massive to weakly stratified, well to poorly sorted loamy, sandy and silty erosion surface sediment. Map unit includes Qnw2 Owd Owd Qal Od Qnw2 Od some areas mantled with less than two meters (6.5 ft) of Peoria Formation- silt (loess) or sand facies. Overlies massive, fractured, firm glacial Qnw2 Om Od Om Qpsr till of the Wolf Creek and/or Alburnett formations. Seasonally high water table may occur in this map unit. Owd Qwa2 Owd Owd Qpsr 43°20'0"N Qal Qpsr 43°20'0"N Qwa2 Qwa2 Qpsr Qal Od Qps Qps D Od Owd Om Om Od PALEOZOIC Owd Om Om Om Owd Om DEVONIAN SYSTEM Qwa2 Om Owd Om DOwd Qwa2 D Qwa2 Qps Qps Qps D Dw - Dolomite, Limestone, Shale, and minor Sandstone (Wapsipinicon Group) Middle Devonian deposits include the Spillville Formation, Dw Dw Qps Qal up to 19 m (60 ft), overlain by the Pinicon Ridge Formation, up to 2 m (6 ft), for a maximum total thickness up to 21 m (68 ft). The Spillville Dw Om Om Om Formation is dominated by medium to thick bedded dolomite, with scattered to abundant fossil molds, and vugs commonly filled with calcite D Qps Qal Om Owd crystals; basal portion is sandy or silty; a distinctive stromatolitic limestone facies occurs locally in the upper part. The Spillville is quarried for Qps Om Qps Om Qpsr Qps Owd local aggregate and also hosts numerous small springs. The Pinicon Ridge Formation is dominated by shaly, laminated or brecciated, Dw Qal Qnw2 Qpsr Dw Om Om unfossiliferous limestone and dolomite. Om Qps Om Qal Dw Qps Qal D Qal Qal ORDOVICIAN SYSTEM Qnw2 Om Qal Om Qps Qps Dw Qps Qps Om - Shale, Limestone, and Dolostone (Maquoketa Formation.) A nonresistant slope-forming unit of up to 40 m (131 ft) of interbedded Dw Om D Om argillaceous limestone, dolostone and gray and brown shale. Fragmentary trilobite and graptolite fossils are common in the basal Elgin Qps Om DD D Qps Limestone Member, and chert nodules are notable in the middle Fort Atkinson Member. It forms an upper confining unit that bounds a karst Om Dw Om Qal Qnw2 Om Qps system in underlying Dubuque,Wise Lake and Dunleith formations of the Galena Group, and may host sinkholes in its lower portion. Dw Om Qps Dw Dw Qal Qal Om Qpsr Dw D Qps Qal Owd - Limestone and minor Shale (Wise Lake Formation and overlying Dubuque Formation, both of the Galena Group) A prominent ledge Owd Om D and cliff-forming unit of up to 31 m (102 ft) of limestone with thin interbedded gray shale beds in the upper 6 m. This map unit is the upper of Om Om Qwa2 Om Om Qwa2 two successive major cavern and karst-forming bedrock units in the area. The Wise Lake Formation consists of 21 m (67 ft) of medium to Qwa2 Qps Dw B thick-bedded, relatively chert-free limestone, portions of which exhibit a distinctive bioturbated fabric; it serves as a source of concrete A Om Om Om aggregate. The Dubuque Formation consists of 10 m (34 ft) of crinoidal limestone and thin interbedded shale. Sinkholes are common to Om Qps Om Qpsr Om abundant within this map unit. Qnw2 Om Qps Qwa2 Dw Om Om Owd D Qps Om Om OmD Od - Limestone (Dunleith Formation of the Galena Group) A prominent ledge and cliff-forming unit of up to 42 m (137 ft) of limestone with Owd Od Dw minor thin interbedded shale. This is the lower of two successive major cavern and karst-forming bedrock units in the area. The formation Qnw2 Qnw2 Om Qnw2 Qal Om Om consists of fossiliferous limestone and argillaceous limestone with common chert nodules; it is commonly quarried for aggregate. Major Qps Qnw2 D springs occur near it’s base and sinkholes and karst features are common. Om D D Qnw2 Qnw2 D Om D Qwa2 Om Om Om Om Om Odpg - Shale, Limestone, and Dolomite (Decorah, and underlying Platteville, and Glenwood formations) A nonresistant slope-forming unit Om Odpg Qnw2 of green-grey shales, dense limestones, argillaceous limestones, and dolostone with average thickness of 26 m to 27 m (85 –90 ft). Along steep Om Qal Dw valley wall slopes large detached slump-blocks of overlying Dunleith Formation limestone often rest on the upper surface of this unit. The unit Om Dw Om Qal D Om forms a regional confining unit that serves as the basal boundary of the karst system in the overlying Dunleith, Wise Lake and Dubuque Dw Om D Dw 43°17'30"N Dw formations of the Galena Group. The upper division, the Decorah Formation, consists of 12 m to 14 m (39 – 46 ft) of interbedded fossiliferous Om Om 43°17'30"N Om Dw green-grey shale and limestone. The middle division, the Platteville Formation, consists of 7.5 m (25 ft) of limestone, argillaceous limestone, Om Qwa2 Qwa2 and dolostone; it serves as a source of quarried aggregate. The lower division, the Glenwood Formation, consists of 2 m to 3 m (7 – 9 ft) of Om Qwa2 Om green-grey shale with minor siltstone to fine sandstone. This map unit, especially the upper and lower subdivisions (Decorah and Glenwood Qal Qwa2 Om D Om Dw Om Qps formations), is rarely exposed and is commonly mantled by 0 m to 2 m (0 – 6 ft) of Quaternary age colluvium. Om Om Om Qal D D D Om Om Dw Dw D D Drill Holes Dw Dw Qwa2 Qwa2 Qwa2 D Om Dw Outcrops Dw Dw Om Om Qal Dw Qps Qps Om Om Om Om Om Om Om Qps Adjacent 7.5' Quadrangles Qwa2 Qwa2 D Qal Om

Qwa2 Om Om Quadrangle Location CRESCO_NE BLUFFTON BURR_OAK Qpsr Qal Qwa2 LYON OSCEOLA DICKINSON EMMET Om WINNEBAGO WORTH MITCHELL HOWARD WINNESHIEK ALLAMAKEE Om KOSSUTH SIOUX OBRIEN CLAY PALO ALTO Qal HANCOCKCERRO GORDO FLOYD CHICKASAW

FAYETTE CLAYTON PLYMOUTH CHEROKEEBUENA VISTA HUMBOLDT BREMER Dw Om POCAHONTAS WRIGHT FRANKLIN BUTLER Om Om BLACK HAWKBUCHANAN DELAWARE DUBUQUE WOODBURY IDA WEBSTER Dw Om SAC CALHOUN HAMILTON HARDIN GRUNDY DD Om CRESCO_SE RIDGEWAY DECORAH JACKSON JONES MONONA TAMA BENTON LINN Dw D CRAWFORD CARROLL GREENE BOONE STORY MARSHALL Om CLINTON D Qnw2 CEDAR HARRISON SHELBY AUDUBON GUTHRIE DALLAS IOWA POLK JASPER POWESHIEK JOHNSON SCOTT Om Om Qal Dw D Om MUSCATINE Om Om POTTAWATTAMIE CASS ADAIR MADISON WARREN MARION MAHASKA KEOKUK WASHINGTON LOUISA Om MILLS MONTGOMERY ADAMS UNION CLARKE LUCAS MONROE WAPELLO JEFFERSON HENRY Om DES MOINES Qal FREMONT PAGE TAYLOR RINGGOLD DECATUR WAYNE APPANOOSE DAVIS VAN BUREN Om Qnw2 PROTIVIN FORT_ATKINSON CALMAR LEE Om Om Om Qal

Qnw2 Qwa2 Om Om Om Qal Om D Om Qal D Qwa2 Qnw2 Qwa2 Om Base map from USGS Ridgeway 7.5' Digital Raster Graphic (IGS GIS file DRGC39.TIF) which was Qwa2 Qal scanned from the Ridgeway 7.5' Topographic Quadrangle map, published by US Geological Survey in 1981 Qwa2 Topographic contours and land features based on 1975 aerial photography, field checked in 1977 Dw D Om 43°15'0"N Land elevation contours (20' interval) based on NGVD 1929. Qal Om Qwa2 Qnw2 43°15'0"N Iowa Geological Survey digital cartographic file ridgeway08quad_surficial.mxd, version 8/28/08 (ArcGIS 9.2) Map projection and coordinate system based on Universal Transverse Mercator (UTM) Zone 15, datum NAD83.

The map and cross section are based on interpretations of the best available information at the time of mapping. Map interpretations are not a substitute for detailed site specific studies. 92°0'0"W 91°57'30"W 91°55'0"W 91°52'30"W 1:24,000 0 0.5 1 2 3 4 Miles 0 0.5 1 2 3 4 Kilometers GEOLOGIC MAPPING OF THE UPPER IOWA RIVER WATERSHED: ± PHASE 4: Ridgeway 7.5’ Quadrangle

Iowa Geological Survey Open File Map 08-04 August 2008

prepared by GEOLOGIC CROSS-SECTION A-B Stephanie Tassier-Surine, Robert McKay, Huaibao Liu, and James D. Giglierano

A B Iowa Geological Survey, Iowa City, Iowa

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) E ACKNOWLEDGMENTS

We thank the staff of the Northeast Iowa RC & D for their efforts in helping to initiate this mapping project and for supporting our 900 900 work in the Upper Iowa River watershed. New subsurface geologic data was generated by the University of Iowa students Thomas Marshall and Kelly Wilhelm who produced descriptive logs of water well drill samples. Luther College in Decorah actively participated in the project through subcontract 07-7380-01 for field mapping support. Luther College students Gabriel Demuth and Carl Haakenstad were participants in field and office work in support of the mapping effort. Birgitta Meade of Luther College was instrumental in accurately locating and elevating water wells in the map area. Drilling in selected sites was provided under contract by Aquadrill, Inc. of Swisher, Iowa. Special thanks to Joel and Patty Kruse who graciously allowed access to their land for drilling. Deborah Quade, Iowa Geological Survey (IGS) lent support with Quaternary field and office expertise; Robert Rowden (IGS) participated in part of the field work; Amy Sabin (IGS) prepared well samples for stratigraphic logging; Brian Witzke (IGS) provided valued information concerning the Ordovician and Devonian stratigraphy of the area; and Andy Asell and Chris Kahle (IGS) provided GIS mapping technical help. Assistance obtaining drilling records and geologic information was provided by Dave Stanley and staff at Bear Creek Archaeology.