Figure 3: Surficial map of the Blackhawk Quadrangle. Scale 1:24,000. The field area for this study focused on the clayey slackwater terrace of the Equality Formation (in blue). Southwest of that terrace and getting progressively lower in elevation and younger in age are the fluvial sand terraces (Henry I and II), a post glacial alluvial terrace (Cahokia I), and the modern floodplain (Cahokia II). The full map may be downloaded at: http://www.isgs.illinois.edu/maps-data-pub/isgs-quads/b/blackhawk-ed.shtml (Map adapted from Johnson, 2009.)
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