Dragon's Mouth Spring

Overview

Dragon's Mouth Spring is the showstopper of the Mud Volcano area: a cave-like hot spring that seems to breathe. You’ll hear deep gurgles and booms, see rhythmic waves surging from the dark opening, and feel warm “dragon breath” steam roll across the boardwalk. It’s a quick stop with big sensory payoff.

What You’ll See

• A vertical, mouth-like opening that sends up puffs of steam followed by surges of hot water.
• Billowing steam and echoing, animal-like growls from within the cave.
• Nearby mud pots and other acidic features along the same short boardwalk loop, so there’s a lot to see in one stop.

Geology in Plain English

This basin is among Yellowstone’s most acidic. Microbes transform hydrogen sulfide into sulfuric acid, which breaks rock into clay—fueling those bubbling mud pots and that unforgettable sulfur smell. Dragon’s Mouth isn’t a geyser; it’s a hot spring inside a small cave. Steam and gases build pressure inside, sending sound and water pulsing outward. It’s also a changeable feature: surging action decreased after 1994, and in 1999 its temperature dropped about 10°F and the water shifted from green to chalky white for reasons not fully understood.

Cultural Notes

Long before the current name stuck, Indigenous peoples knew and used this area. The Crow described the steam bursts as the snorts of an angry bull bison—an image that fits the drama you’ll witness.

Wildlife

Bison frequently move through Mud Volcano. They look mellow until they’re not—give them space and never step off the boardwalk to go around wildlife.

Visiting Logistics

• Location: On the Mud Volcano boardwalk loop just south of Hayden Valley.
• Access: It’s a very short walk—think minutes—from the paved parking lot. Expect a brief stair climb to the main viewing spot.
• Facilities: Parking and restrooms are by the lot. Informational signs help make sense of what you’re seeing.

Tips for the Experience

• The sulfur smell here is potent; some visitors notice it can hang in the car if you park right beside Mud Caldron.
• Pause and listen—those rumbles and waves are half the show.
• Combine with the rest of the loop to see Mud Volcano and other “dragon” features in one go.

Best Time to Visit

Go early or late to sidestep the midday crowds and tour buses. Cooler morning or evening air makes the steam more dramatic, and you’ll have an easier time snagging parking. Midday is still worth it if that’s when you’re passing through, but expect more people.