Once across the dam follow the trail to the right, it will follow the edge of the lake. It goes from 2 track to single track, after 1/2 mile or so you will come to a fence/gate which you can cross. There is braided trails follow the dominant trail, and you will come to a 2 track which is more like a double track, follow this for many miles up a ravine it will turn into single track. It is a good workout up the hill and nice views of the lake. When you are nearing the end you will ride across a burned area that is now a meadow and will cross an old barbed wire fence, the trail goes right. You follow this downhill towards the lake and will go through an aspen grove, the trail kind of dies out at the bottom but you can ride left along the shore and end up at a beach at the lake (turn around and follow the same trail out) It is ~7.5 miles one way. There is a nice game trail which continues north and south along the lake from the beach, but needs pruning to ride a bike, and would make a good loop trail eventually. It is a great ride and the only real single track I have really found in Pinedale. Enjoy!
From Pinedale take Fremont Lake Road about 5 miles turn left onto FS RD 111 that goes to the Lakeside Lodge and boat ramps. Stay left at the fork pass the Lodge and CCC Ponds turn off, the paved road will curve to the right and ends at the boat ramp, go straight on the dirt road and you will end at the dam and dirt parking lot. Park here and take bike across the dam. Note you can also park at the CCC Ponds and ride a nice trail to the dam 1/2 mile or so.
http://www.singletracks.com/item.php?c=1&i=4903