This map shows the different kinds of bedrock in Michigan. Bedrock influenced ice movement during past glaciations, and most of Michigan is on soft bedrock that was easy for the glacier to move through and grind away. Because of this, most bedrock in Michigan is deeply buried beneath glacial material. One place where bedrock is close to the surface and strongly influences ecosystems is in the Niagaran formation along the southern edge of Upper Michigan. Niagaran bedrock outcrops are often  associated with the occurrence of rare species. Data sources are the 1:500,000 maps by R.L. Milstein, 1987, "Bedrock geology of southern Michigan", and R.C. Reed, "Bedrock geology of southern Michigan", published by the Michigan Department of Natural Resources.