Here is a MICHIGAN OpenStreetMap Garmin .img file containing all of the off-road trails as ROUTABLE roads.
Here is link to my google drive:
It is MI_6-9-wide.img
copy it into the /garmin folder on your gps. Some of you will have to rename it to gmapsupp.img in order for your GPS to recognize it.
Here is a DIFFERENT GPX file with ROUTES built for MI-6-9-wide map
It is much easier to follow a route with turn-by-turn guidance.