The seasonal roads are in the Yankee Springs/Middleville area. One of the starting points is on South Yankee Springs Road from there you just kinda follow the trails around.
The address on google maps for this trail is
3998 S Yankee Springs Rd
There are also some that are a little ways away from these trails. Theres a decent amount of trails that you can spend a good few hours exploring!
Another start to the trail is on Gun Lake Road
6898 Gun Lake Rd
Rutland Charter Township, Michigan
Again, the address comes up as this on google maps...Not sure how accurate this will be....This trail doesn't show up on maps as a road.
Let me know if you have any questions/and or meet up and go out sometie
Ive also heard of some trails in the Allegan State Forest, but haven't actually gone there yet.