Geologic Map of the Scott City 7.5-Minute Quadrangle, Scott and Cape Girardeau Counties, Missouri

The Scott City quadrangle is located at the northern end of the Mississippi embayment (fig. 1). The quadrangle contains parts of three physiographic features: the abandoned channel of the ancestral Mississippi River, the Benton Hills, and the flood plain of the ancestral Ohio River and modern Mississippi River. These features are largely the manifestation of the Quaternary evolution of the Mississippi and Ohio Rivers, the chronology and analysis of which has been discussed by Fisk (1944), Saucier (1968, 1974, 1994), Guccione and others (1990), Madole and others (1991), Autin and others (1991), Porter and Guccione (1994), and Blum and others (1995a,b). The relatively flat area in the northern part of the quadrangle is part of the abandoned Mississippi River channel that was active prior to the river's diversion through Thebes Gap in the adjacent Thebes 7. 5-min quadrangle at approximately 10.6 ka (Porter. and Guccione, 1994). This area periodically is inundated by Mississippi River floods, except for the land protected by a manmade levy (af) maintained by the U.S. Army Corps of Engineers. Within the abandoned channel, alluvial-fan deposits (Oaf) derived from the surrounding uplands have prograded over alluvial fill (Oma). The bedrock outcrops at Lost Hill and an adjacent hill in sec. 4, T. 29 N., R. 13 E., were former islands in the ancestral Mississippi River. The uplands area that makes up most of the quadrangle is part of the Benton Hills, the northernmost extension of Crowley's Ridge (fig. 1). Geometrically, the Benton Hills resemble a tilted block dipping to the north-northwest. The highest topography in the Benton Hills occurs at the extreme southeastern margin along a drainage divide between the modern Mississippi River flood plain to the southeast and the severely underfit Ramsey and Caney Creeks. Stream-gradient profiles along Ramsey and Caney Creeks indicate that their original headwaters were removed by either erosional or tectonic processes (Palmer and Hoffman, 1993). These two creeks, as well as Sals Creek, provide surface drainage to the north and west for this part of the Benton Hills; all contain extensive Pleistocene terrace deposits (Ot) that are mantled by loess (dominantly Peoria) producing a subdued topographic expression. The towns of Scott City and lllmo are partly situated on a paleo-channel of the ancestral Mississippi River, which also contains loess-mantled terrace deposits on grade with those in Ramsey Creek. In the extreme southeastern corner of the quadrangle, the small