In Yakima County on the Ahtanum Multiple Use Area, the Gray Rock Trailhead provides access to 23 miles of ATV riding.
To reach the Gray Rock Trailhead (aka Tree Phones Campground trailhead): Tree Phones Campground is located on the Middle Fork of Ahtanum Creek, 15 miles from Tampico, WA. From I-82 (north or southbound), take the Valley Mall Boulevard exit, then head west on Valley Mall Boulevard. Turn left on 3rd Avenue and head south to Ahtanum Road, and turn right onto Ahtanum Road. Follow Ahtanum Road westerly to Tampico. At the Tampico junction, bear right onto the North Fork Road. At the end of the pavement, bear left onto the Middle Fork Road. You should pass just south of the ranger station gate. Stay on this road to Tree Phones.
Overall, Gray Rock Trailhead is the 14th most popular ATV riding trail of all 35 ATV trails in Washington.