East of Seattle and northwest of Snoqualmie Pass, the Middle Fork Snoqualmie River Trail is an easy scenic mountain bike route through old growth forest. The trailhead is near Dingford Creek Falls, and the trail runs up to the Alpine Wilderness boundary (9 miles). At the boundary, the trail continues as the Dutch Miller Gap Trail up to the summit (another 5.5 miles).
To reach the mountain biking trailhead from Seattle, head east on US90 for 34 miles to Exit 34 at Edgewick Road. Proceed north on Edgewick Road to junction with FS5620. Bear right on FS56 (Middle Forck Snoqualmie Road). Continue 6 miles to Dingford Creek Trailhead.
From the trailhead parking area, head across the bridge to the trail. Continue east heading upstream.
FYI - Theres a nice side trail at the 1.5 miles point which leads up to Snow Lake (4 miles one-way). Its inside the wilderness boundary.
Overall, Middle Fork Snoqualmie River Trail is the 20th most popular mountain bike trail of all 59 mountain biking rides in Washington.