By Tara Anthony, Penn State University Libraries
Geological maps are a valuable resource for understanding characteristics of earth properties through rock and mineral formations. Historical geological maps held within map collections can span geographic areas and be useful for understanding regions across administrative regions, such as state borders. The BTAA Geoportal can be a source for identifying where to look for historic geological map collections within BTAA institutions. This blog post will highlight what types of geological maps are able to be located from the BTAA Geoportal as of Spring 2025. Geological maps are a resource type for narrowing down specific map types. See this search for Resource type (Geological maps) for results. These historic geological maps are primarily from the early half the 1900s, with some earlier geological maps as well that date back to the mid-1800s. Of the results, the following institutions have materials classified as geological maps discoverable from the BTAA Geoportal: Penn State University, University of Michigan, Indiana University, University of Minnesota, The Ohio State University, Northwestern University, and University of Maryland. These historic geological maps can also be seen within the BTAA Geoportal's Libraries Historical Maps Collection. Of the 1,354 geological maps, 1,160 geological maps are from Penn State University's Bituminous coal mine maps of Pennsylvania.
Highlight on the Bituminous coal mine maps of Pennsylvania
The Bituminous coal mine maps of Pennsylvania cover the following counties: Allegheny, Armstrong, Beaver, Bedford, Blair, Bradford, Butler, Cambria, Cameron, Centre, Clarion, Clearfield, Clinton, Elk, Fayette, Forest, Fulton, Greene, Huntingdon, Indiana, Jefferson, Lawrence, Lycoming, Mercer, Somerset, Sullivan, Tioga, Venango, Washington, and Westmoreland. These were maps made by the Works Progress Administration during 1934-1938. Some information included on these maps include mine information, oil and gas wells, and handprinted notes, as available.
This is an example of a map from the Bituminous coal mine maps:
Altoona-01-LF; Altoona-1; Lower Freeport, BTAA Geoportal record, Penn State Libraries Digital Collection Record.
More about the Penn State University Libraries Bituminous coal mine maps collection, and Index to Bituminous Coal Mine Maps of PA.
Additional Examples of Historical Geological Maps
Additional examples of geological maps of regions provide opportunities to study historical geological features. For instance, a geological map from the 1880s (Geological map of the region between the Ontonagon River, Michigan, and Numakagon Lake, Wisconsin) (Digital Collection Item Description) from the Penn State University Libraries Special Collections cover parts of Michigan and Wisconsin.
Geological map of the region between the Ontonagon River, Michigan, and Numakagon Lake, Wisconsin, BTAA Geoportal record, Penn State University Libraries Digital Collection Record Description
When exploring geological maps and historical maps, the BTAA Geoportal can be a helpful resource for determining collections of interest among institutions and across geographic borders.