GIS-BASED DELINEATION OF THE BURIED PRE-QUATERNARY WYALUSING RIVER VALLEY IN EAST-CENTRAL WISCONSIN, USA

Depth-to-bedrock maps (Trotta and Cotter, 1973) and previous research (Stewart, 1976) have long recognized the presence and general trend of a buried bedrock valley in east-central, Wisconsin. Emergent research on the organization of pre-Quaternary drainage systems in the Midwest and North American mid-continent (Carson et al., 2018) merits closer consideration of the geologic context of this buried valley system.

To better delineate the valley, we accessed 115,176 logs of water wells from 19 counties aligned along a broad transect stretching from south-central Wisconsin into the southern corner of the Upper Peninsula of Michigan. The locations of wells were precisely geo-located in ArcGIS to accurately identify ground surface elevation. Wells that could not be located accurately enough to identify ground surface elevation were removed from consideration; wells that did not contain relevant depth to bedrock information were also removed. After processing, 60,186 well records remained to develop a buried bedrock topography map. A best estimate for the floor of the valley was visually identified, and then all wells within 500 m on either side of that line were queried in ArcGIS. When plotted on distance vs. elevation, these data identify that the valley grades to the northeast at a slope consistent with mid-continent alluvial valleys.

Carson et al. (2018) identified remnants of a pre-Quaternary river valley in the Driftless Area of southwestern Wisconsin. They interpreted this to represent part of a late Cenozoic river system that drained to the Gulf of St. Lawrence, rather than to the Gulf of Mexico as it does today. The buried bedrock valley delineated here connects to the surface expression of this ancestral ‘Wyalusing River’ at the proper elevation and slope such that it must be a downstream continuation of this river system. These data and interpretations assist with further refining our understanding of the pre-Quaternary drainage systems of central North America.