METHOD FOR RECOGNIZING LOCAL BEDROCK INFLUENCE ON DRIFT PLAINS*

Analysis of topographic and bedrock surface data from 41 sites 23.3 km² (9 m²) within Midwestern areas glaciated during the Late Wisconsinan identifies an average drift thickness-maximum bedrock relief transition equation for the presence or absence of bedrock surface influences on topographic detail. For sites with average drift thicknesses between 15 and 35 m, the transition occurs when average drift thicknesses exceed 0.5 maximum bedrock relief + 10 m. This equation may provide a practical tool in searching for buried bedrock valleys.