Geological Maps
Geologic maps are the most effective tools for presenting geologic information to users in the public and private sectors, and are remarkable for their ability to portray local geology in a regional context. Geologic maps convey a variety of data about surface and subsurface earth materials, and represent a valuable resource for those interested in earth processes, products, and landscape history. The following information is summarized from our 12-page Wisconsin Geologic Mapping guide, which is available free from the SCO.
- The Need for Geologic Maps
- Types of Geologic Maps
- Recent Developments in Geologic Mapping
- Status of Geologic Mapping In Wisconsin
- Obtaining Geologic Maps
The Need for Geologic Maps
Geologic maps are needed by a variety of individuals and organizations who require detailed information about the earth's surface. These include industry and agriculture for various land use and siting projects; the private and public sectors for protecting groundwater resources and assessing geological hazards; local, state and federal agencies for facilities siting and evaluation; and the educational community.
The Wisconsin Land Information Program (WLIP) has stressed the importance of geologic maps in the generation of modern land information data for use at the local, county and state levels. Geologic data is fundamental to wise land use and development, and must be linked with other natural resource and land information databases to provide a context for land use planning.
Types of Geologic Maps
Geologic maps convey information about local and regional geologic setting, and are produced to depict surficial or bedrock materials. Surficial geologic maps typically show unconsolidated materials such as stream and lake deposits, glacial and meltwater deposits, coastal deposits, wind-laid deposits, and slope deposits. Bedrock maps show the distribution and characteristics of solid rock formations where they occur at the land surface and where they are buried by younger surficial deposits.
In Wisconsin, surficial maps are commonly referred to as Pleistocene geology maps because they show the distribution of materials that have been deposited during various periods of glaciation throughout the Pleistocene Epoch (between 10,000 and 2,000,000 years before present).
Recent Developments in Geologic Mapping
The U.S. Geological Survey (USGS) established a National Geologic Mapping Program in 1988 in response to the growing demand for geologic information (and obsolescence or discontinuation of many geologic maps and map series). This program was created to coordinate federal, state, and university mapping activities and to augment the development of new mapping and publication technologies. Congress passed the National Geologic Mapping Act in 1992 to expedite formation of a comprehensive federal-state geologic database.
Status of Geologic Mapping in Wisconsin
The Wisconsin Geological and Natural History Survey (WGNHS) is the lead agency for the production and maintenance of geologic maps and information for Wisconsin, and coordinates activities with the USGS, which fulfills a similar role at the national level. Today, the primary initiative of the WGNHS is the production of a series of 1:100,000-scale (1"= 1.6 mi.) county folios that include maps and explanatory text. Depending on the county, these folios include maps that cover Pleistocene/Quaternary geology, bedrock geology, soil attenuation potential, hydrogeology, depth to bedrock, and mineral resources.
The WGNHS considers counties for mapping based on environmental-land use and economic concerns and available funding. Local needs and funding sources, and the Survey's research priorities drive the selection process. Two to three county maps are typically in progress each year, most of these currently involve Pleistocene and hydrogeologic mapping.
In addition to the county folios, WGNHS has published geologic maps of the state at scales of 1:250,000 (1"= 4 mi.) and 1:1,000,000 (1"= 16 mi.). The WGNHS maintains a web site that includes samples of some of these maps. Among them are maps of : Thickness of Unconsolidated Material (208 Kb), Groundwater Contamination Susceptability (259 Kb), and Bedrock Geology (454 Kb).
Map scale determines how much geologic detail can be shown. In Wisconsin, the general purpose county folio geologic maps at the 1:100,000-scale represent the highest level of detail that is commonly available. The WGNHS believes that map production at scales larger than this (e.g., 1:24,000 - 1"= 2,000') is more appropriately the responsibility of the private sector due to the greater cost and higher demand as special purpose products. Although regional, multi-county maps (1:250,000-scale) and maps that cover the entire state (1:1,000,000) are accurate at the scales they are produced, they are best used as general reference and educational tools.
Obtaining Geologic Maps
Geologic maps and related information can be obtained directly through the WGNHS. The Survey's annual list of publications provides a comprehensive guide to what is available.
The USGS also has products that may be of more specialized interest. Items such as maps, digital elevation data, planimetric data, land use and land cover data, and geographic names information are available through the Earth Sciences Information Centers (ESICs). For more information or a complete listing of current mapping projects in other regions of the country, contact the USGS Mid-Continent Mapping Center.
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