This cover consists of surface and near-surface faults compiled bythe IllinoisBasin Consortium in a multiyear project. This part of the projectended around 1994 and resulted in a publication by the Gas ResearchInstitute. The report, cited in a cross-reference, contains apaper map titled "Major structural features of the Illinois Basin."We received a digital copy of the map in dxf format, and edited itto include only the faults.Our intent is to show the overall pattern of faults, and to showthe location of the main exposed and near-surface faults forcomparison to deep subsurface structures. We made little attempt toedit details of the digitized faults, beyond adding tick marks toindicate dip directions of a few normal faults. For details suchas exact locations, fault dips, separations, and crosscuttingrelations, users should consult the original geologic maps citedin the Gas research Institute publication.