Moss Lake is a small King County Natural Area with a few trails; they may be overgrown and suffer from lack of maintenance. However, in addition to the trails on the official Natural Area, there are connector trails to Hancock Timber's Snoqualmie Forest lands, with its maze-like miles of logging roads and trails, some of which to the north of the Natural Area are named and signed with very small markers. If you ride north far enough, you'll encounter the eastern section of the Tolt Pipeline. (If you ride the pipeline here, stay on the side trail and off the pavement if you can. Logging and other maintenance can result in large-vehicle traffic on this narrow road).
NOTE: Campbell Global requires a $50 annual/$8 day permit to ride on their lands. More Information
The trail begins at a metal gate to the east of the parking area; there's a "tank trap" obstacle to keep out motorized vehicles that will require your horse to step over a couple of logs.
The gates to the parking area are locked in the evening by King County Sheriff personnel, so don't ride too late.
From Duvall, go south on 203 to Big Rock Road and turn left. Follow Big Rock Road 5 miles to where it intersects with Kelly Rd/Lake Joy Rd and turn left (north).
From Carnation, go north on 203 and turn right onto NE Stillwater Hill Raod, which becomes Kelly Road.
Where Kelly Road and Lake Joy Road fork, go right to continue on Lake Joy Road, which changes name after a couple of miles, becoming either NE 120th St or E Lake Joy Drive (not to be confused with W Lake Joy Drive, to the right). After another mile and a half, turn left onto Moss Lake Road and follow it about a half mile to its end where there is a loop parking area.
Open
Length: 1-3 miles within the Natural Area, many more miles to the north and east.
Surface: dirt, gravel, some muddy and rooty areas. Some of the forest-land trails have some rocky areas on logging roads.
Share with: hikers, mountain bikes
Pit toilets
Parking for: 4-5 trailers
King County Natural Area:
http://www.kingcounty.gov/environment/waterandland/natural-lands/ecological/moss-lake.aspx
Map:
Trail map courtesy Evergreen Mountain Bike Alliance
Moss Lake trails plan (only covers official Natural Area)