The loop starts at Grizzly Campground in West Yellowstone. I had forgotten to turn the track log on for the first 8 miles or so, I filled it in with a route. Basically, go to Iris Street, make a left and continue on to Plateau Road. Everything up to Warm River is wide groomed snowmobile trail/road. There's a locked gate about 14 miles in on Plateau Road/FR1700 that I squeezed around. Then another gate just past the Idaho state line that you can open and close. I was heading east on Flagg Ranch road, but I was keeping an eye on my fuel supply and didn't find the ranch so I turned back. Your other options are to head north into Yellowstone or south into Grand Teton. Jackass trail was pretty good and worth the effort. Grassy Lake's discharge was nice too, but it's a haul back there with not much more than dusty road with a fair amount of traffic. I now wish I had done Cave Falls while I was down there instead of that haul out on Flagg road. I got a little confused at Warm River Campground. I had read on the Targhee NF website that there is a abandoned railroad grade that runs from the campground to the Montana border. When I reached the campground, a sign at the entrance said it was closed to ATV's and motorcycles?? What up? I tried to find access to the railroad grade by going northeast out of the campground which just returned me to where I had been earlier that morning. Backtracking and continuing up 47, I found the trail head. The tunnel is not far from the trail head. Take the trail head under the highway and turn left onto the railroad grade. I had planned to take the grade to the Montana border, but terrible storms blew in and I jumped off the railroad grade on FR315 and took the highway back to the campground in the wind/rain/hail. Total miles was about 230. Map of today's ride.