This is a great trail to bring the kids and have them ride out to one of the swimming/wading areas in the river. You might have to help them at some of the creek crossings though.
The trail starts at the Conasauga River trailhead off of Peavine Sheeds Creek Road (FS 221). The trail is mostly singletrack now but it follows a (very) old rail bed very close to the banks of the Conasauga River. It's a very pretty ride and a number of trails lead down to swimming or wading areas in the river.
While the trail is pretty flat, except for a couple of the creek crossings, enough roots and rocks have made their way back into the railbed that this is definitely not a rail trail. The singletrack is pretty wide at the beginning as it's used for access to the cool Conasauga River, and you'll find a good number of people there on a hot summer day. As you get further from the trailhead, the singletrack can become pretty narrow through the vegetation.
There are half a dozen or so small to medium creek crossings, so plan on getting a little wet. Some of these get messy as the trail sees some horse traffic. A few rocks in the trail as well as a couple of creek crossings keep it from meriting an easy rating. Particularly towards end, you'll have some impressive rock walls to your left. It seems the rail bed was probably cut into the terrain.
The riverside trail becomes Iron Mountain Trail (#77)
at the terminus shown here. The Iron Mountain Trail (#77)
eventually fords Conasauga River about a mile downstream, beginning a steep ascent. Nominally, the Conasauga River Trail (#61) actually continues to the north at this point forming a loop with Sheeds Creek Peaving Road (FS 221), but it's not clear if this section is open to bikes or not, so I haven't shown it here.