Mud Volcano Trail

Overview

This compact loop showcases some of the park’s most acidic and animated hydrothermal features—think churning mud, hissing steam, and that unmistakable “rotten egg” smell. The loop is short (0.6–0.8 miles total, about 118 feet of gain) and usually takes 20–30 minutes, but it packs in a surprising amount of drama. Surfaces are primarily boardwalk with some paved sections, and railings appear where exposure or features warrant them.

Route and Accessibility

If you want the gentlest grades, go clockwise; starting from the south side of the lot makes the climb more gradual. The first ~0.2 miles counterclockwise is mostly gentle (about 5% or less). Beyond that, expect steeper sections (8–12%) and some stairs. A shorter lower loop is wheelchair-accessible: from the northeast end of the parking area, follow the lower loop, then turn left at the junction after Mud Volcano to return. Designated accessible parking and accessible restrooms are by the large paved lot.

What You’ll See

Highlights come rapid-fire. Dragon’s Mouth Spring exhales steam and rhythmically splashes inside a cavern-like opening. Mud Volcano—once a tall cone before an 1872 explosion—still gurgles and steams. Grizzly Fumarole hisses with escaping gases. Sour Lake’s acidic waters are colored by microbes that thrive in sulfur-rich conditions. Black Dragon’s Caldron dramatically appeared in 1948, blowing out trees and coating the area with mud; it’s still churning. You’ll also pass Churning Cauldron, Sizzling Spring/Basin, Mud Geyser (which reportedly launched 20–50 feet in the 1800s), and the stark “Cooking Hillside,” where superheated soils killed trees in the late 1970s.

Geology in Plain English

Here, microbes convert hydrogen sulfide gas into sulfuric acid. That acid chews rock into clay—voilà, bubbling mudpots. The chemistry also explains the pungent sulfur smell and the yellow-to-gray palette. This basin sits near caldera uplift/subsidence and a convergence of faults, an area scientists watch closely for ongoing activity.

Wildlife and Safety

Bison frequently wander through—sometimes right on the boardwalks. Give all wildlife space (at least 25 yards) and be ready to turn back if animals block the route. In spring, grizzly bears may be nearby, feeding on winter-killed animals; carrying bear spray is wise. Never leave the boardwalks—hydrothermal ground and water can cause severe burns. Supervise kids closely, don’t run or shove, and leave the area if gases make you feel unwell. Temporary closures happen for bear or bison activity, so stay flexible.

Best Time to Visit

Arrive early to beat crowds and enjoy a quieter boardwalk experience. This is a quick stop that pairs well with nearby Lake and Hayden Valley viewpoints. If you love mudpots but prefer fewer people, consider adding Artist Paintpots to your day. The area is open 24/7; a park entrance fee is required.