Cobblestone Loop
The Cobblestone Loop is a lariat-shaped extension off the Glenwild Trail, with a connection at the top to the newer Flying Dog trail. Most riders don't do Cobblestone alone as a ride, but combine it with Glenwild or Flying Dog. But you CAN drive to the loop.
The loop itself is in a heavily-wooded area. The top of the loop nicks a new development, where (as of 2007) roads are in place, but no homes. It's pretty, and the trail is nice, if short.

The trail is worth doing as an extension off the Glenwild Loop -- up, around the loop, and back down, then backtracking on Glenwild (milder ride, if you came up counterclockwise on Glenwild) or continuing through the full Glenwild loop (hammerhead ride). If you're doing Flying Dog, you'll hit one side of the loop then ride the connector down to Glenwild.
The connector to Glenwild isn't as scenic, but it's smooth and easy riding. The bottom portion near Glenwild is fairly flat with sagebrush and grass. Near the loop itself, you're in a small canyon among small cottonwoods.

Location of Cobblestone on the Glenwild Loop: 
If you started on Stealth and went over the top of Glenwild clockwise, look for the trail at mile 4.4, about 1/2 mile after descending to the sage-covered valley. Go L uphill on Cobblestone.
If you went counterclockwise around Glenwild, find Cobblestone in sage brush at mile 3.8 as you approach the hills. Go R uphill.
0.0   Fork off Glenwild    N40 44.756 W111 31.279
0.6   Cross paved road    N40 45.204 W111 31.558
0.9   Fork Cobblestone Loop    N40 45.365 W111 31.750
Left    1.4  Cross road       N40 45.549 W111 31.793
           1.7  Fork R (L=Flying Dog)     N40 45.704 W111 31.573
           2.4  L at fork, bottom of loop
Right   1.6 Fork L (R=Flying Dog)    N40 45.704 W111 31.573
           1.9 Cross road     N40 45.549 W111 31.793
           2.4 R at fork, bottom of loop
3.3 Back at Glenwild trail

Getting there, Glenwild Trailhead: At the I-80 Park City exit, go north (left from the exit if you're coming from SLC) to the frontage road. Turn right. About 1/4 mile later at the second road on your left, turn left. Find the trail parking area just before the northbound road crosses the creek. (You'll see the trail map kiosk and bathroom). GPS N 40° 43.662' W 111° 32.051'. Head up the road to start your ride. To begin on the Stealth Trail, turn right on singletrack just past the bridge. To ride counterclockwise up Glenwild to Cobblestone, turn right and climb the hill.