Black Dragons Caldron

A seething black mudpot with a dramatic 1948 origin story

InsideYellowstone National Park

Overview

Black Dragon's Caldron is one of the Mud Volcano area’s headliners—a dark, seething mudpot that looks (and smells) like something out of a fantasy novel. It sits just off the boardwalk loop near Hayden Valley, in one of the most acidic corners of the park. Expect constant bubbling and steam, plus that unmistakable sulfur scent.

What You’ll See

From the boardwalk overlook you’ll peer into a churning pool of black mud, spattered rims, and drifting steam. It’s less explosive today than decades ago, but still feels alive and unpredictable. Interpretive signs here make it easy to grasp what you’re looking at—and why this spot is so unusual.

Geology & Backstory

This feature literally burst onto the scene in 1948, blasting out trees and creating a new mud-filled crater. Since then, it has migrated roughly 200 feet along a subsurface fissure—proof that Yellowstone’s plumbing is always rearranging itself. The caldron’s waters are highly acidic (around pH 2). Microbes use hydrogen sulfide rising from deep below, helping create sulfuric acid that breaks surrounding rock into the silky clay “mudpots” are known for. Its formation likely diverted heat from nearby Sour Lake, which was more active before the caldron appeared.

Wildlife

Bison commonly wander through this basin and may pass right by the boardwalks. Give them plenty of space—at least 25 yards—and let them have the right of way. It’s an unforgettable scene when the wildlife and the mudpots share the stage.

Planning & Access

Park at the Mud Volcano lot and follow the signed boardwalk loop; Black Dragon’s Caldron is one of several features along the route. Restrooms are at the parking area, but there are no food or services within the basin. Activity and access can change with hydrothermal shifts, and the mud’s consistency can vary with seasons and precipitation, so obey any temporary closures.

Best Time to Visit

Go early to beat tour-bus crowds and snag parking. Shoulder seasons tend to be calmer. If you’re sensitive to sulfur odors, keep this a quicker stop.

Pros

Vigorous bubbling mudpot with a dramatic 1948 origin and ~200 ft migration
Boardwalk viewpoint with helpful interpretive signs along the Mud Volcano loop

Cons

Strong sulfur (rotten-egg) smell
Parking and crowds peak mid-summer

Tips

Park at the Mud Volcano lot and follow the boardwalk loop to the caldron.
Arrive early or in shoulder seasons for easier parking and fewer crowds.
Expect a strong sulfur smell—plan a shorter stop if you’re sensitive to odors.
Give bison lots of space; never crowd wildlife on or near the boardwalks.
Check for temporary closures; hydrothermal activity can change access without notice.