Ahtanum Multiple Use Area is a perfect place for all around ATV fun. Included within the park boundaries are Ahtanum Meadows and Ahtanum Camp. These are located on Middle Fork Road, across from one another. Ahtanum is a large enough area to fall under the Wenatchee National Forest, and Goat Rocks Wilderness, but is state managed. It is made up of public and state lands which border the Yakima Indian Reservation.
Ahtanum is wild enough in which an ATV user can become lost. The DNR has terrific maps that are color coded as to trail use. There are a number of users here including ATV users. There are surprising views of the Cascades around fantastic climbs, and a look at the eastern deserts through the foliage. You can even cross over into the Wenatachee on ATV if you'd like. The park is open all year, but in the winter season is only open to snowmobiles. Spring and summer is peak ATV/ORV riding time.
Of all the parks in Washington State, Ahtanum is the driest; it is advisable to carry some spare air filters on your ATV trip, nothing dramatic here, just keep them in the trunk of the car "in case." The rides here are as challenging as you want them; there is something for every ATV skill level, with a nice central base camp location. If you live close enough, this could be a place to go every weekend for the summer, honing ATV skills before pushing on to a challenge run, maybe even an ATV trip out of state.