The bedrock of Mercer County was formed by sediments deposited in oceans, lakes, and swamps. Over time, compaction and lithification created the sandstone, shale, and limestone formations found beneath varying depths of glacial deposits. Glacial deposits throughout the region vary from 0 to 400 feet thick and are a result of the retreat of the Kent Ice Sheet of the Wisconsinan Glacier between 10 and 15 thousand years ago. Oil and natural gas are present in the Devonian and Mississippian bedrock of the county, with the main production occurring in Devonian Age formations. A low sulfur coal was present in the Sharon Formation and was mined for use in blast furnaces through the 19th century. Little of this remains. A lower grade coal, present in the Brookville, Scrubgrass, and Kittanning coal seams, was also mined in the county through the late 20th century.
Please visit the PA Geological Survey for additional subsurface geologic information