Near Gold Bar, Washington, Reiter Pit has ATV trails for the serious ATV sport person. It's big enough to ride through without seemingly finding the end. It's open all year, and is not yet charging any fees. Park where your car and haul are out of the way, just be space respectful for anyone else who may show up. Oh, make sure your gear includes a helmet; this could be a rough ride.
Reiter Pit is an area made up of round rock and gravel. Most of the trails reflect this. There are forested areas, but mostly you'll be seeing the forest through the trail, since the trails don't get into too much tree area. Because of all the hard landscape, it is advisable to take children to 'softer" ATV parks. This might be a perfect place for teens to sharpen driving skills. They can't be too rough without the trail being rough right back. Make sure to pack basic first aid supplies, bandages and such things. Also, pack plenty of water or sports style drink, it's easy to get dehydrated without knowing it, even the "grown up" kids do it.
This ATV area is a nice weekend trip. It is an entertaining spot for most ATV levels above beginner. The one basic rule the park as is: keep ATV/ORVs off the pavement, but, with all the rock around, what ATVer wants to ride on pavement. Keep an ATV journal, and be sure you make room in your plans to write up an ATV trip to Reiter Pit.