Kind of short notice but D Day Adventure park is going to have their annual trail stomp this weekend. It's $20 per ATV for the weekend to get in and have primitivr camping or RV hookups. They will also have an ATV Rodeo, drag race, mud pit, obstacle course, and a 5 mile timed race through the trails, these are all free to compete in. The Park is located in Wyandotte OK about 20 miles south of Joplin. Pretty good trails, some easy that the kids can ride and there are some very technical as well.
http://ddayadventurepark.com/trail-stomp