Arkansas ATV Park
You may be thinking of Superlift in Hot Springs. It is set up for rock crawlers but there are also atv trails.
Or Byrds Adventure Center near Cass, Arkansas along the Mullberry river.
Both have camp grounds, both are set up for rock crawlers but have atv trails.
Both have showers.
Byrds is better because it is in the middle of the Ozark forest which has some great trail riding that is still legal. You can ride from thier campground to a trail called the water fall trail and then cross over the highway and access the Mill Creek trail system. They have maps on hand that show the area trails that are open.