Lake Michigan, USA: substrate classes

A composite map of substrate composition was created from two separate surveys of surficial sediments of Lake Michigan.  For Lake Michigan south of Frankfort, a sediment survey map by Powers and Robertson (1968), that essentially corroborated two earlier surveys by Hough (1935) and Ayers and Hough (1963-64), was used.  Sediment composition of Lake Michigan north of Pentwater was available from unpublished Lake Survey data of NOS-NOAA (Great Lakes Basin Framework Study 1976).  We created a composite map by overlaying the northern and southern survey maps, and merging areas of like sediment type.  Distinctive characteristics iclud hard bottom areas along the southwest shoreline (Milwaukee to Gary, IN), depositional areas in southern and northern basins, and a varied mix of sand-hard bottom in reef areas of northeast Lake Michigan.