The Mahomet Bedrock Valley: Its History and Character

The Mahomet Bedrock Valley (MBV), a prominent and important geologic feature in the subsurface of east-central Illinois, has been investigated for over a half century for both its resources and scientific curiosity. It still remains a predominant focus for geologic and hydrogeologic research. During the early part of the Quaternary Period or before, the MBV comprised part of the major midcontinent drainage system, the Teays-Mahomet Bedrock Valley System, which connected the Appalachian Mountains to the Ancient Mississippi River. Following successive glaciations during the pre-Illinois and Illinois episodes, the bedrock valley was filled in and is now deeply buried in the subsurface by glacial and postglacial deposits. This paper provides a review of the past and current understanding of the geologic history, including a detailed description of the MBV's valley-fill stratigraphy, which contains a record of cut-and-fill events associated with multiple ice advances. The MBV was re-used several times to drain meltwater from the advancing ice margins, although the modern drainage network shows no reflection of the ancient bedrock valley system.