Mud Volcano Area

The Washburn Expedition and the Hayden Survey discovered Mud Volcano during the early 1870s. Both groups heard the sound "resembling the reports of distant artillery" for several miles before arriving at Mud Volcano. Mud Volcano at that time exploded with mud from its hillside alcove. Since then Mud Volcano has quieted but still remains a bubbling, seething spring.
Mud Volcano Area, also known for Black Dragon's Caldron, Sour Lake, Mud Caldron, Dragon's Mouth Spring, and Sulfur Caldron, is very acidic. Iron sulfide is responsible for the dark-gray, blacker brown-colored water, while hydrogen sulfide produces the "rotten egg" smell common to the Mud Volcano area.