The buried Mahomet Valley in east-central Illinois is a complex lowland carved into the surface of Pennsylvanian and older rocks. It consists of a deep channel throughout most of its length and contains numerous benches below erosional remnant hills, suggesting several cycles of early to middle Quaternary erosion. Recent local and regional studies utilizing existing borehole data, including down-hole geophysical logs and seismic profiles, have provided new insights into the valley’s configuration. The usual techniques for interpreting shallow seismic refraction and reflection data are complicated by a seismic velocity inversion in the Quaternary sediments filling the deeper parts of the...