Get geo fabric, roll out, put gravel on top. How thick the gravel needs to be is based on the load.
Having an ATV with 4wd, and oversized tires, I'm surprised it can't go through? Mine can drive over stuff I can't walk through, especially if there is a vegatation mat.
We have some corduroy roads here through swamps. They plain suck when they get old. Traffic will work gravel down through. Once the logs are bursting out, you get stuck in mud holes full of logs.
The ground is well over 2 feet of peat -- soft, spongy stuff at best, sink deep into it mud at worst. With years of decaying rhodedendrum mixed in. Will geo fabric and gravel really be appropriate?
I've been riding ATVs for 30 years, in all kinds of terrain. This multi-feet deep stuff is just not possible -- there's no tranaction and the tires sink right into it such that the chassis sits on the ground.