The Michigan Office of Geological Survey appears to have pdf versions of all the documents in their Digital Geological Library available for download. The transcripts of some early (beginning in 1871) field notes are a fun inclusion in the available archives. Actual GIS data was a bit hard to find although I found both bedrock geology and quarternary geology available from the state Geographic Data Library in shapefile format. I also found oil and gas well data but did not download it.