Illinois County Geologic Maps

Samuel V. Panno, Donald E. Luman, and Dennis R. Kolata 29 pp., large-scale map, and digital appendix

Jo Daviess County in northwestern Illinois is part of the Driftless Area, which includes portions of Wisconsin, Minnesota, and Iowa. Here, the soils and unconsolidated materials are relatively thin, and coupled with the highly fractured dolomite bedrock, create a geologic setting for a prolific karst aquifer within the region. During the extreme summer drought of 2012, mysterious vegetated lines began appearing in agricultural fields within Jo Daviess County. The presence of these vegetated crop lines was an ephemeral event lasting only a few months, and ISGS researchers responded quickly to document it. The results of on-site investigations and image interpretation of aerial photography acquired from June to October determined that the vegetated crop lines are an accurate reflection of the buried bedrock fracture system in northwestern Illinois, which had heretofore been restricted to direct observation in available road cuts, quarries, and bedrock outcrops. Digitized data sets of these vegetated crop lines can be used in conjunction with alignments of cover-collapse sinkholes and mine diggings to better characterize the geometry and character of the karst aquifer within the Driftless Area of northwestern Illinois, and to better understand the regional tectonics of Illinois and nearby states.

Bedrock Geology of Chana Quadrangle, includes two 34" x 28" map sheets; sheet 1 contains map and legends; sheet 2 includes descriptive stratigraphic column, 2 cross sections, 2 figures, and descriptive text. USGS-STATEMAP contract report, 2 sheets, 1:24,000. Authors: Delpomdor, F., Wirth, H., 2018.