Health, Economy Top Priorities for Illinois’ Geologic Mapping Experts

Detail of the new Pope County bedrock geology map centering near Eddyville, just released by ISGS.

Each September a group of specialists gather at the University of Illinois campus to consider priorities for the coming year’s geologic mapping of the state.

The priorities developed by the Illinois Geologic Mapping Advisory Committee (IGMAC) have important implications for the wealth and the health of the state. The group, composed of consulting geologists, state and federal officials, industry representatives (insurance, mining, and water), and academics met in Champaign on September 8.

Thanks to 165 years of work by the Illinois State Geological Survey, a division of the Prairie Research Institute, geological mapping has made a growing contribution to the development of industry in the state, access to groundwater supplies, and prevention/mitigation of pollution.

IGMAC endorsed short (2-5 year completion) and long-term (5-10 year completion) priorities for bedrock mapping and for surficial mapping (from the bedrock to the surface). The Advisory Committee is required by the National Geologic Mapping Act of 1992 to assure that cooperative mapping efforts are aligned with societal needs in participating states. The mapping targets are 56 square mile, 1:24,000-scale, topographic quadrangles. Illinois has over 1,000 of these quadrangles, all surveyed in the early 1800s and named by a municipality in each one. The priorities will be submitted to the U.S. Geological Survey’s STATEMAP program as a competitive funding request.

ISGS has just released on-line the bedrock geology map for Pope County as well as new geologic maps of the following quadrangles: Eldorado, Hamburg, Mokena, Mahomet, and Mount Carmel. The preliminary maps can be downloaded from STATEMAP is a component of the National Cooperative Geologic Mapping Program (, which provides federal funds for detailed two-dimensional geologic mapping to state geological surveys.

The following topographic quadrangles, and reasons for study, were endorsed for FY 2017 as priorities.

Short-term mapping priorities for surficial mapping:

  • Palos Park (Cook County) and Tinley Park (Cook and Will Counties) – to locate sources of groundwater and construction aggregates.
  • Monticello (Piatt County) – to understand and protect the Mahomet Aquifer, and to better estimate connections between surface water and groundwater.
  • Mount Pleasant (Whiteside County) – to locate sources of groundwater and construction aggregates and to better understand Lake Carlyle sedimentation and earthquake hazards.
  • Lawrenceville (Lawrence County) -- to locate sources of groundwater and construction aggregates, to map terraces, flood plains, and meander cutoffs, and to find evidence of ancient earthquakes.

Short-term priorities for bedrock mapping:

  • Kampsville (Calhoun County) – to evaluate landslide potential induced by rock failure, and construction aggregate resources.
  • Baldwin, Steeleville (both in Randolph County), and De Soto (Jackson County) –- to evaluate potential for low-sulfur coal, as well as oil and natural gas deposits.

Finally, the Sandwich Fault Zone (stretching from west of Joliet to south of Rockford in Northern Illinois) has drawn particular interest from the geology community recently. This region of high and growing population was added to the state’s short-term priority list after the Illinois State Water Survey demonstrated significant differences in groundwater quality and quantity on each side of the fault zone, and requested assistance to better understand the geological conditions responsible for the differences. Therefore, the Chana Quadrangle in Ogle County was selected as the initial area to investigate. 

The advisory group also endorsed the addition of three bedrock study areas to the long-term priority list: (1) Rock Island County where population density is high, (2) extreme northwestern Illinois focusing on Jo Daviess County and Galena, and (3) a broad section of western Illinois extending north from East Saint Louis.

Two-dimensional maps produced by these programs have a resolution of one inch equals 2,000 feet on the ground (~2.5 inches per mile), a scale that is detailed enough for local planning. The maps are valuable for studying land-use, groundwater resources, waste siting, geologic hazards, aggregate resources, and many other uses. ISGS is also a leader in state-of-the-art 3D mapping technology which offers far more detailed subsurface information on water and mineral resources. The Survey has proposed these superior technologies as a priority for future geologic mapping in Illinois.

That is true particularly in population centers where the need for industrial water, drinking water, water for energy production, solid waste disposal, access to sand and gravel and limestone/dolomite aggregate minerals for construction, and other municipal requirements make understanding of underground resources critical. Economic development and regional land- and water-use planning greatly benefit from complete geologic mapping information.

Previous priorities led to the completion of maps for the Chicagoland counties of Lake and McHenry, maps which were delivered to those counties in 2015. Will County is now in the fourth year of a five-year schedule. All of these county deliverables show considerable detailed information of the subsurface (e.g. sand and gravel aquifers) and they provide local officials with science-based tools to deal with rapid development, population growth, and environmental protection.

“Today those three counties are among the most thoroughly mapped anywhere,” according to Richard Berg, the Illinois State Geologist and ISGS director. “Without such information, multi-million dollar mistakes can be made regarding use and protection of water resources and disposal of wastes in sensitive areas. Detailed mapping greatly can reduce potential liabilities associated with economic development because often costly hazards can be discovered early and avoided.”