USGS Home
Contact USGS
Search USGS

Preliminary integrated geologic map databases for the United States:

Minnesota, Wisconsin, Michigan, Illinois, and Indiana

By: Suzanne W. Nicholson, Connie L. Dicken, Michael P. Foose, Julia A.L. Mueller

Version 1.1

Updated December 2007

Choose state or scroll down Illinois Indiana Michigan Minnesota Wisconsin

Introduction

The growth in the use of Geographic Information Systems (GIS) has highlighted the need for regional and national digital geologic maps attributed with age and lithology information. Such maps can be conveniently used to generate derivative maps for purposes including mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This Open-File Report is a preliminary version of part of a series of integrated state geologic map databases that cover the entire United States.

The only national-scale digital geologic maps that portray most or all of the United States for the conterminous U.S. are the digital version of the King and Beikman (1974a, b) map at a scale of 1:2,500,000, as digitized by Schruben and others (1994) and the generalized digital version (Reed and Bush, 2004) of the Geologic Map of North America (Reed and others, 2005a, b) compiled at a scale of 1:5,000,000. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis for this product. In a few cases, new digital compilations were prepared (e.g. Ohio, South Carolina, South Dakota) or existing paper maps were digitized (e.g. Kentucky, Texas). Also as part of this series, new regional maps for Alaska and Hawaii are being compiled and ultimately new state maps will be produced.

The digital geologic maps are presented in standardized formats as ARC/INFO export (.e00) files and as ArcView shape (.shp) files. Accompanying these spatial databases are a set of five supplemental attribute tables that relate the map units to detailed lithologic and age information. The maps for the CONUS have been fitted to a common set of state boundaries based on the 1:100,000 topographic map series of the United States Geological Survey (USGS). When the individual state maps are merged, the combined attribute tables can be used directly with the merged maps to make derivative maps. No attempt has been made to reconcile differences in mapped geology across state lines.

Procedures

The various digital geologic maps that form the basis for this product were originally produced in a wide variety of formats. Although most of them are available as ARC/INFO export (.e00) files and/or ArcView shape (.shp) files, the items and formats in the polygon (PATs) and arc (AATs) attribute tables vary dramatically. To unify these disparate maps, it was necessary to create a set of standard formats, and then to convert the state digital geologic maps to conform to these standards. The details of these standards are presented in the documentation of this report. The creation of a unique map unit name, called unit_link, allows the different State maps to be merged. (Database field names are in italics). Unit_link consists of a two-letter State (ST) code, concatenated with the original geologic map unit name, which may be slightly modified to remove special characters for age designations, followed by a semicolon, and an integer that designates geographic regions (or provinces) within the map. For those states where provincial structure is absent, this integer is simply "0". This variable, unit_link, can then be used as a key field to relate the tables that contain age and lithologic information to the spatial database (.dbf).

Compilation of a regional geologic map always requires compromises between the complexity of geologic information for a large region, and the need to keep the compiled map, and its explanation, relatively simple. Similarly, compromises are necessarily made in order to convert the large variety of formats in our source maps into the standard set of formats developed for this series.

Typically, spatial databases were modified from the source in the following general manner: The most recent data was obtained and the arcs and polygons were reattributed in the PAT according to the nomenclature adopted for this series (see documentation in this report and the metadata for individual spatial databases). When this reattribution was complete, the other attributes from the original spatial databases were deleted. Generally, if faults were not an integral part of the spatial database, arcs were retagged to make them so. Additionally, for those states where faults were mapped, fault arcs were extracted and provided as a separate .e00 or shape file (faults_dd, faults_lcc).

A second more detailed set of standardized attribute tables was generated by extracting information from the legends of the source maps and entering it into a set of five tables that record map unit information (STunits), lithologic information (STlith), age information (STage), and references (STref and STref-link). Some existing map legends provided an inadequate level of age or lithologic information. In these cases, we consulted the scientific literature, maps at smaller scales, and, in some cases, the original authors of the compilations or other regional experts. When we used updated information, it was recorded in the STage and STlith tables. Thus, the age and lithology information in these attribute tables may, in some cases, conflict with the information on the legends of the original source maps that may have been compiled decades ago.

In particular, the lithology table (STlith) may be much more extensive than the information in the map legends. Large regional compilations like these state maps often utilize map units that encompass a variety of lithologies. Volcanic rocks are commonly “lumped” extensively, combining tuffs, ash-flow tuffs, flows, and subvolcanic intrusions of a number of compositions, so that individual map units may contain dozens of unique lithologies. Although a dominant (most abundant) lithology has been designated for all map units, users are advised to be cautious, as many map units simply have no single dominant lithology.

Bedrock state geologic maps are typically compiled on the basis of lithostratigraphic units. In areas of variable metamorphic grade, this leads to inherent difficulties when trying to classify these units by rock type. For instance, a single stratigraphic unit may contain rock types ranging from shale to gneiss or limestone to marble. Commonly these gradations are not noted by internal contacts within a stratigraphic unit on the geologic map. However, the stratigraphic unit descriptions found in map explanations may include both metamorphic and non-metamorphic rock names. This combination results in apparent inconsistencies when assigning rock types within a single stratigraphic unit and may be particularly notable when a stratigraphic unit crosses a state boundary.

Our approach to assigning rock types to the lithostratigraphic units was to begin by using the information provided by the state in the map explanation. If information was lacking, other references including the USGS National Geologic Map Database “Geolex” website ( http://ngmdb.usgs.gov/Geolex/geolex_home.html ) were used. This website is an on-line search tool which provides usage, location, type locality, unit descriptions, age and bibliographic entries for lithologic and geochronologic unit names.

Error correction is an ongoing process with most spatial databases. A typical state spatial database consists of tens of thousands of polygons and arcs, and errors introduced during the creation of these spatial databases are inescapable. One common type of error is data coding that does not conform to the original paper map. For example, polygons may be given the wrong map unit, or faults may be called normal faults instead of thrust faults. Some of these errors are unavoidable because, in a few cases, the original paper map cannot be interpreted with certainty.

Spatial databases are provided in both Lambert Conformal Conic projection and geographic coordinates (NAD27, decimal degrees).

Projection:	Lambert Conformal Conic
Horizontal datum:	NAD 27
Spheroid:	Clarke, 1866
Standard parallels:	33 degrees North
	45 degrees North
Central meridian:	-100 degrees
Reference Latitude:	0 degrees
Horizontal units:	meters
False easting:	0
False northing:	0

Supplemental attribute tables are provided in Filemaker Pro format (.fp5), in dBase format (.dbf), and comma-separated value (.csv) text.

ArcView files can be viewed with the free viewer, ArcExplorer, which can be downloaded from http://www.esri.com/software/arcexplorer/.

References

King, P.B., and Beikman, H.M., 1974a, Geologic map of the United States: U.S. Geological Survey, scale 1: 2,500,000.

King, P.B., and Beikman, H.M., 1974b, Explanatory text to accompany the geologic map of the United States: U.S. Geological Survey Professional Paper 901, 40 p.

Reed, J.C. and Bush, C.A., 2004, Generalized Geologic Map of the Conterminous United States, U.S. Geological Survey, scale 1:7,500,000. (URL http://pubs.usgs.gov/atlas/geologic/)

Reed, J.C., Jr., Wheeler, J.O., and Tucholke, B.E., 2005a, Geologic map of North America: Geological Survey of America, Decade of North American Geology, 3 sheets, scale 1:5,000,000.

Reed, J.C., Jr., Wheeler, J.O., and Tucholke, B.E., 2005b, Geologic map of North America – Perspectives and explanation: Geological Survey of America, Decade of North American Geology, 28 p.

Schruben, P.G., Arndt, R.E., and Bawiec, W.J., 1994, Geology of the Conterminous United States at 1:2,500,000 Scale — A Digital Representation of the 1974 P.B. King and H.M. Beikman Map, U.S. Geological Survey Digital Data Series 11, release 2. (URL http://pubs.usgs.gov/dds/dds11/)

To download files, right click on the file that you want and either Save target as...(Internet Explorer) or Save link as...(Netscape).

Illinois

In 1996 the Illinois Geological Survey produced digital bedrock geology files by digitizing the 1967 paper state-scale bedrock map by H. B. Willman, John C. Frye, Jake A. Simon, Kenneth E. Clegg, D. H. Swann, Elwood Atherton, Charles Collinson, Jerry Lineback, and T. C. Buschbach. The digital files have undergone minor revisions since then (see metadata accompanying downloadable spatial data). No version numbers have been assigned to the revised digital versions, so this and all previous digital versions are arbitrarily assigned as version 1.0. This data can be freely downloaded from the Illinois Natural Resources Geospatial Data Clearinghouse at http://www.isgs.uiuc.edu/nsdihome/webdocs/browse.html but cannot be redistributed (see metadata).

Data Modifications

The spatial data for Illinois in this report have been modified in several important ways. The description and referencing of these changes is tabulated in the file metadata.

The original coverage boundary was replaced with the standardized common state boundary derived from Digital Line Graphics (DLG) files: thus, one or more polygons for coastal water were added to fill in the area between the physical coastline and an off-shore state boundary.

Notes on rock type attribution

For a review of how rock types were coded, see above and an additional discussion in the documentation.

[STATE LIST] [BACK TO TOP]

Indiana

The Indiana Geological Survey digitized and modified the existing published paper map of the bedrock geology of the state (Gray, Ault, and Keller, 1987). The data can be freely downloaded from: http://igs.indiana.edu/arcims/statewide/download.html BEDROCK_GEOL_MM48_IN is a polygon shapefile that shows bedrock geology of the state of Indiana at a scale of 1:500,000. The mapped stratigraphic units include systems and selected groups, formations, and other stratigraphic units.

Data Modifications

The spatial data for Indiana in this report have been modified in several important ways. The description and referencing of these changes is tabulated in the file metadata.

The original coverage boundary was replaced with the standardized common state boundary derived from Digital Line Graphics (DLG) files: thus, one or more polygons for coastal water were added to fill in the area between the physical coastline and an off-shore state boundary.

Notes on rock type attribution

For a review of how rock types were coded, see above and an additional discussion in the documentation.

[STATE LIST] [BACK TO TOP]

Michigan

The digital bedrock map of Michigan was produced by the USGS by digitizing recent published regional compilations (Milstein, 1987; Reed and Daniels, 1987; Sims, 1992), ranging in scale from 1:500,000 to 1:1,000,000. Some minor modifications and generalizations have been made from the published maps based on recent detailed fieldwork, particularly in northern Michigan. The digital bedrock geology of Michigan used in this Open-File Report is derived from the three-state compilation that was published in 1997 by the U.S. Geological Survey as Open-File Report 97-455. The data can be downloaded freely from: http://pubs.usgs.gov/of/of97-455/. Display of this map at significantly larger scales may produce small errors in locations of contacts or faults relative to features contained in other data sets.

Data Modifications

The spatial data for Michigan in this report have been modified in several important ways. The description and referencing of these changes is tabulated in the file metadata.

The original coverage boundary was replaced with the standardized common state boundary derived from Digital Line Graphics (DLG) files: thus, one or more polygons for coastal water were added to fill in the area between the physical coastline and an off-shore state boundary.

Notes on rock type attribution

For a review of how rock types were coded, see above and an additional discussion in the documentation.

[STATE LIST] [BACK TO TOP]

Minnesota

The bedrock map of Minnesota was originally digitized in 1994 by the Minnesota Geological Survey, and updated in 1996 based on subsurface information available at the time. Subsequently, the Minnesota Geological Survey recompiled and modified the digital bedrock geology files in order to create the year 2000 version of the state bedrock map at a scale of 1:1,000,000. This map combines the 1996 state bedrock coverage with more recent mapping derived from county atlas projects (1:100,000) and other maps at scales ranging from 1:48,000 to 1:200,000. Due to the scale, some units have been modified, dropped, or combined with others during the compilation process. The Minnesota Geological Survey provides these spatial data free of charge: these data can be freely downloaded from: http://www.geo.umn.edu/mgs/currentpubs.htm then click on MGS anonymous ftp 1, folder s-20_3ed.

Data Modifications

The spatial data for Minnesota in this report have been modified in several important ways. The description and referencing of these changes is tabulated in the file metadata.

The original coverage boundary was replaced with the standardized common state boundary derived from Digital Line Graphics (DLG) files: thus, one or more polygons for coastal water were added to fill in the area between the physical coastline and an off-shore state boundary.

Notes on rock type attribution

For a review of how rock types were coded, see above and an additional discussion in the documentation.

[STATE LIST] [BACK TO TOP]

Wisconsin

The digital bedrock map of Wisconsin was produced by the USGS by digitizing recent published regional compilations (Mudrey, Brown, and Greenberg, 1982; Sims, 1992), ranging in scale from 1:500,000 to 1:1,000,000. Some minor modifications and generalizations have been made from the published maps based on recent detailed fieldwork, particularly in the northern Wisconsin. The digital bedrock geology of Wisconsin used in this Open-File Report is derived from the three-state compilation that was published in 1997 by the U.S. Geological Survey as Open-File Report 97-455. The data can be downloaded freely from: http://pubs.usgs.gov/of/of97-455/. Display of this map at significantly larger scales may produce small errors in locations of contacts or faults relative to features contained in other data sets.

Data Modifications

The spatial data for Wisconsin in this report have been modified in several important ways. The description and referencing of these changes is tabulated in the file metadata.

The original coverage boundary was replaced with the standardized common state boundary derived from Digital Line Graphics (DLG) files: thus, one or more polygons for coastal water were added to fill in the area between the physical coastline and an off-shore state boundary.

Notes on rock type attribution

For a review of how rock types were coded, see above and an additional discussion in the documentation.

[STATE LIST] [BACK TO TOP]

References for maps

BEDROCK_GEOL_MM48_IN: Bedrock Geology of Indiana (Indiana Geological Survey, 1:500,000, Polygon shapefile available at http://igs.indiana.edu/arcims/statewide/download.html)

Gray, H.H., Ault, C.H., and Keller, S.J., 1987, Bedrock Geologic Map of Indiana, Indiana Geological Survey Miscellaneous Map 48.

Milstein, Randall L. (compiler), 1987, Bedrock geology of southern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale 1:500,000.

Morey, G.B. and Meints, Joyce, compilers, 2000, Geologic map of Minnesota, bedrock geology (3 rd edition): Minnesota Geological Survey State Map Series S-20, scale 1:1,000,000.

Mudrey, M.G., Jr., Brown, B.A., and Greenberg, J.K., 1982, Bedrock geologic map of Wisconsin: Wisconsin Geological and Natural History Survey, Scale: 1:1,000,000.

Reed, Robert C., and Daniels, Jennifer (compilers), 1987, Bedrock geology of northern Michigan: Geological Survey Division, Michigan Dept. of Natural Resources, scale 1:500,000.

Sims, P.K., 1992, Geologic map of Precambrian rocks, southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Map I-2185, scale: 1:500,000.

Willman, H.B., Frye, J.C., Simon, J.A., Clegg, K.E., Swann, D.H., Atherton, Elwood, Collinson, Charles, Lineback, Jerry, and Buschbach, T.C., 1967, Geologic map of Illinois: Illinois State Geological Survey, scale 1:500,000.

[STATE LIST] [BACK TO TOP]