The region is a small mountain range that runs mostly north and south on both sides of the main road from Nalaikh to Baganuur. Elst Uul (which means Sandy Mountain) is the highest point on the south side of the road. It is about four to five km off the road.
The trails are a random network of two track (not double wide) and some singletrack both etched into the landscape primarily by the local herdsmen and illegal wood cutters. Some of the track is still used enough to be maintained as two track. Some of it has reduced to singletrack due to a lack of use. Most all of it is great for riding.
This is classic cross country riding in the Mongolian wilderness. There are trails to be explored running pretty much in all directions across the range. Bring satellite images and a compass and enjoy the adventure. The climbs are big but pretty much completely rideable if you are in good enough condition. The descents are FAST and mostly three to six miles long. The trail mileage listed (40 miles) is purely a ball park guess and probably a conservative estimate.