The wife and I stumbled on this area while searching for some old trails outside of Gold Bar, WA. It's an area currently being constructed specifically for ORVs and 4x4s with lots of hiking trails as well. A Discover Pass IS REQUIRED.
Here's a link to the DNR website, which includes plans, trail specs, schedule, current progress, volunteer information, and maps.
We only traversed a small portion of the trail as I don't have that experience level just yet, but much of it was passable in the XJ with open diffs, Rustys 3.5" lift, sway disconnects, on 31s.
There were four other gentlemen out there with winches and fully locked rigs, they are obviously a little more serious than I am and they did the existing .5 mile loop in around 4 hours. They had said they'd done it before and really enjoyed the area. I'll upload a couple photos, but I honestly didn't think to take too many.