Here's the legal places in Michigan that I've ridden so far:
Click the link to get pics and review of the trail.

Atlanta Trail  (Atlanta, MI)

Black Lake Trail (Onaway, MI)

Bull Gap Trail (Mio, MI)

Big Bear & Crapo Creek Trail (Lewiston, MI)

Gladwin Trail (Gladwin, MI)

Mio Trail (Mio, MI)

North Branch Route (Lewiston, MI)

Old State House Trail (Glennie, MI)

The Meadows Trail (Luzerne, MI)

The Mounds (Flint, MI)

Silver Lake Sand Dunes (Silver Lake, MI)