GIS-BASED DELINEATION OF A BURIED BEDROCK VALLEY IN EAST-CENTRAL WISCONSIN

Recent and on-going research (Carson et al., 2013) is documenting that the lower Wisconsin River valley was incised by an east-flowing river (opposite of the modern west-flowing Wisconsin River). Coring and geomorphic evidence suggest that through much of the Cenozoic, a single river followed the course of the upper Mississippi River as far south as its current confluence with the Wisconsin River, and then made a tight left turn flowing east along the valley now occupied by the lower Wisconsin River. Direct evidence for this river channel is obscured east of Sauk City, WI, by late Wisconsin (MIS 2) glacial deposits. In order to identify the downstream continuation of this proposed river valley, the use of ArcMap GIS and well construction reports (WCR’s) from the Wisconsin Department of Natural Resources provided the basis for developing a bedrock elevation map of east-central Wisconsin.

WCR data were acquired for twelve counties in east-central Wisconsin; within this area, over 75,000 well records were collected. The WCR data were processed to verify that all records were accurately geolocated, ensuring that each record was associated with an accurate ground-surface elevation. Records that could not be accurately located were removed from the analysis. The WCR data were then filtered to remove well records that did not provide useful information about depth to the buried bedrock surface, and further processed to remove closely-spaced, redundant records. This resulted in approximately 16,000 well records that were used to resolve bedrock topography. These verified points were processed with an ArcMap raster interpolation tool to identify the location and trend of the buried bedrock valley, as well as the higher bedrock surfaces on either side of the buried valley.

The bedrock topography defined by this work refines evidence presented by Stewart (1973) for a deep, buried channel extending northeast from the Sauk City area through Marinette County. The location and gradient of this buried valley is consistent with it being a downstream continuation of the east-flowing river identified in southwestern Wisconsin.