I don't live in Jacksonville or else I'd join the club. A friend that lives in Jacksonville says there are some sand dunes somewhere, but I haven't been able to find them.
If the dunes are the dunes I'm thinking about they are marked no trespassing.
I know of two spots. One down Old Jennings Road, and one down 220. Its a power line trial. Very very sticky mud. Doesn't splatter, just chunks flying.
I wish I could find some more places to go and some people to go with. I have a Jeep Cherokee. If you want to figure something out to do let me know we can plan a play date. haha