It's not the destination, its the trip
Smoky Mountain, on the Grand Staircase-Escalante National Monument, gets its name from coal fires that are burning under the mesa. They were likely ignited by lightning several thousand years ago, and have kept burning ever since. At some places the coal heat and smoke escapes via small pits in the surface of the mesa. In other cases there are large fissures. In places where the coal has completely burned, you will see large areas of collapsed ground, almost like sinkholes.
The drive to the "trailhead" though is really the highlight. The road leaves Bigwater, Utah, and traverses a moonlike landscape of eroding Tropic Shale badlands. The Tropic was deposited during the Cretaceous period at the bottom of the inland sea, and numerous marine reptiles have been found within it.
After passing the Warm Creek turnoff, the road heads towards a line of cliffs. At first the way is not obvious, but then you begin to see the road - it rises precipitously up the slope and cliffs to the east. Driving up the narrow, winding, one-lane road offers amazing views across the lower end of Lake Powell. You are climbing up through the rocks as well, going from the Tropic to the Calico to the John Henry and finally the Wahweap Formations. There is a handy place at the top of Kelly's Grade to take pictures off the road and the basins below.
After driving across the top of the mesa and taking the views, you eventually come to a series of cracks in the ground. This is where the active fires are located. Pull off the side of the road and begin hiking around. There isn't really a trail, just free-form exploration of the pits. You can tell the active ones when there is some smoke (occasionally) or the bad smell rising from the earth. Some places there are large mounds of rock on top of some of the fissures, where locals attempted to fill in the cracks and stop the fires. They were concerned the fires would eliminate all the coal deposits and they wouldn't be able to mine it. Fortunately, the entire area was made a National Monument by President Clinton, eliminating that prospect. From the pits, enjoy views south towards Navajo Mountain, east towards the Kaparowitz, and north towards the Aquarius Plateau. Once you have wandered at your leisure, return via the same route.
As a warning, the road crosses three washes (Wahweap, Crosby, and Warm Creek) that can wash out during thunderstorms, leaving the unprepared motorist stranded. Take caution if storms are in the area, and do not attempt to cross a flowing wash.
Check out the Triplogs.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.