East of Seattle and Issaquah, the Tiger Mountain trail system is popular with local mountain bike riders. The East Tiger Mountain area has over a 20 mile network of trails and forest roads. It does get muddy and also crowded on the weekends, so go early and often. The singletracks are open from April 15th to October 15th. One of the more popular downhill mountain biking routes that gets a lot of play is the Preston Railroad Trail. This is a great place to go when dry -- if it has rained recently, it can be miserable.
To reach the Tiger Mountain trailhead for mountain biking from Seattle, head east on US90 to Exit #25 for SR18. Head southwest on SR18 for 4.1 miles to the East Tiger Summit. Turn right heading north into Tiger Mountain State Forest. There is a large parking lot immediately off SR18. If you continue up to the left into the forest, after about 0.5 miles you will find the main trailhead parking area.
The most popular route from the main trail head parking area is to start up the Iverson Connector to Tiger Mountain Road. Head west up Tiger Mountain Road for 3 miles to the summit. Turn right heading northwest on Preston Railroad Trail descenting for 3 miles to the access road. Turn left for about 500 feet to East Side Road #700. Turn right on East Side Road #700 heading south for about 3 miles. Veer right on Northwest Timber Trail for 2 miles leading back to Tiger Mountain Road near Iverson Connector back to the main parking area. From this point, many riders add on the Iverson Loop riding clockwise.
If you are looking to do some mountain biking in the West Tiger Mountain area, keep in mind that only Puget Power Trail and High School Trail are open to mountain bikes.
Note: As of July 2011, a Washington DNR Discover Pass is required to use the Tiger Mountain trailhead parking areas. If you do not have a pass, then you will get a $99 ticket. This can be obtained online at: http://www.discoverpass.wa.gov/
Note: As of September 2011, the Iverson Loop is temporarily closed for maintenance and logging operations.
Overall, Tiger Mountain is the 4th most popular mountain bike trail of all 59 mountain biking rides in Washington.