South of Hayden Valley and on the east side of the lower loop of Yellowstone's main road is the mud volcano area, an area of boiling mud pots, fumaroles, and hot springs. It is one of the worst-smelling areas as well. The main area is near the road and there is a short loop around some of the main features. There is also a short trail up the hill and back to Sizzling Basin, Sour Lake andd Black Dragon Cauldron. These photos are all of features in the lower area, this of Mud Volcano itself.