Mud Volcano Trail

Mud Volcano Trail is an easy, roughly 0.6-mile loop of pavement and boardwalk through Yellowstone mudpots, springs, and fumaroles. It starts and ends at the same parking area by different trailheads. Allow one to two hours with stops. Start at the south trailhead and go clockwise for a more gradual climb; the full circuit still has a couple of steep sections and stairs.

The lower loop around Mud Volcano and Dragon’s Mouth Spring meets federal accessibility guidelines. It is a shorter option if the full hillside circuit is too steep. Dragon’s Mouth’s viewing platform has stairs, so you can stay on the boardwalk if you prefer to skip that climb.

Hydrogen sulfide rises from deep underground. Microorganisms use it and help turn it into sulfuric acid, which breaks rock into wet clay. Other gases push through the mud as bubbles. Sulfur minerals color the features yellow and gray, while hydrogen sulfide gives the area its rotten-egg smell. Mudpot consistency and activity change with the seasons and precipitation.

The hills east of the trail are part of Sour Creek Dome, where the ground rises and sinks as the magma chamber below changes. Scientists monitor that movement. Yellowstone’s caldera-forming eruption 640,000 years ago caused a collapse that later filled with lava flows, building much of the volcanic plateau around you.

Bison, sometimes in groups with calves, may walk along the boardwalk. Keep at least 25 yards away and turn back if one blocks the route. Marmots, Clark’s nutcrackers, mule deer, and elk also live here; grizzlies may feed on winter-killed animals in spring. Stay on the boardwalk and designated path around hydrothermal features: the water can cause severe burns. Pets are not allowed. In winter, snow and ice can cover the trail, and access may depend on snowcoach tours and the main park road.