Southeast of Seattle and southwest of Cle Elum, the popular Taneum - Manastash area has 26 miles of trails open to off-road motorcycle trails riding. This trail system consists of loops through valley bottoms to ridge tops.
There are two main trailhead areas. For the Taneum area, the Taneum Junction Campground area is a great place to start. It is located on Taneum Road (FS330) which is east of US90 Exit 93. For the Manastash area, the Buck Meadow region is a great place to start. Try Manastash Campground off Manastash Road (FS3100), which is east of US90 Exit 106.
The popular 4.2 mile ATV 30 Trail runs from the junction of FS3100 and 4W311 at Riders Camp to 4W307.
Note: there is plenty of active logging in the area.
Overall, Taneum - Manastash ORV is the 3rd most popular dirt bike trail of all 38 dirt biking rides in Washington.