Northwest of Grand Rapids and west of Mears in Oceana County, the 3000 acre Silver Lake State Park has a 450 acre ORV area with sand dunes (aka Silver Lake Dunes) that is open to ATV riding.
To reach the ATV riding trailhead for the Silver Lake ORV Site from Mears on US31, use the Hart or the Shelby exits and then follow the signs.
Note: avoid weekends and especially holidays. This ORV area is very popular and gets very crowded.
Overall, Silver Lake State Park is the 14th most popular ATV riding trail of all 54 ATV trails in Michigan.