The Fore Mountain trailhead is hard to find off the Stony Run
Trail. It is located near the intersection of the Middle Mountain
Trail (Fore Mountain Trail on GW Map) and Stony Run
Follow the Fore Mountain Trail which is backcountry singletrack. This portion of the Fore Mountain trail takes you out of Douthat State Park and into the George Washington National Forest. The National Forest trails are typically not as maintained as the Douthat trails.
The initial portion of the trail is uphill and then you'll begin some very fun descending. The descent will go from gradual ridge singletrack to a very steep and loose trail. After this steep downhill there is a steep 300' pine needle covered climb. At the top of this climb you'll want to take a left (this is not marked but the straight option is usually blocked).
This next descent will have a number of switchbacks which will lead into some really fun twisty singletrack. This portion of the downhill goes on for a while so enjoy! There is a left hand turn which is not marked but the straight option is usually block (see photo of orange jacket rider).
You'll eventually pop out onto Sulphur Springs Road, which you'll cross. At this point, the trail will climb steeply. Stick with it until you top out on the ridge. At this point, you're in for a long, gradual ridge-top descent followed by a steeper final descent into Covington.