294-4 Geologic mapping to support slope failure mitigation in Crawford County, Wisconsin

Session: Geologic Mapping (Posters)

Presenting Author:

Authors:

Abstract:

The geologic map of the Eastman and Harpers Ferry 7.5-minute quadrangles and Ferryville and Lansing  7.5-minute quadrangles (Crawford County), located in the Driftless Area of southwestern Wisconsin, support the Wisconsin Department of Transportation's ongoing efforts to mitigate slope failures along the Wisconsin State Highway 35 corridor (Highway 35). New observations and lithologic descriptions of the area's geology provide insights on factors controlling slope stability which can be incorporated into future and more detailed slope susceptibility models.

Mapping efforts focused on field observations of slope failures and their relationship to the geologic materials that compose the slopes along Highway 35. These efforts show that intra-unit variations in lithology and weathering characteristics are just as important as inter-unit variations when assessing slope stability.

Building off work by Anderson and others (2022), these new maps suggest that in addition to slope geometry and the type of geologic material composing the cut slopes adjacent to Highway 35 (slopes modified to accommodate the Highway), the variables most strongly influencing slope failure susceptibility in the corridor of concern are the presence and exposure of discrete cliff forming horizons on the slope above the highway. These include of brecciated intervals within the Prairie du Chien Group, resistant facies within the Jordan Formation, and the contact zone between the St. Lawrence Formation and Tunnel City Group. Other factors include the overall steepness of the bedrock surface, the amount of colluvial toe slope material adjacent to Highway 35, and the distance between Highway 35 and the adjacent slopes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8985

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.