Sulphur Caldron

Overview

Sulphur Caldron is a short-but-worthy stop to see one of the park’s most acidic hot springs (pH roughly 1–2). The pool churns and bubbles beside the Grand Loop Road, its sulfur-rich gases giving off that unmistakable rotten egg smell. It’s a raw, elemental display—more about chemistry and power than postcard prettiness.

What You’ll See

Expect an agitated, yellow-tinged cauldron near boiling temperature. On breezy days, steam and fumes can drift across the viewpoint, and the surrounding earth looks barren and clay-rich—classic acid-sulfate terrain. Many visitors spend 10–20 minutes here, often pairing it with the Mud Volcano boardwalks just across the road.

Geology, Simplified

This is an acid-sulfate feature: meteoric water mixes with deep gases (notably hydrogen sulfide). Near the surface, those gases oxidize into sulfuric acid, which drops the pH and dissolves surrounding rock into muds and clays. The result is harsh water chemistry, subdued colors, and constant turbulent bubbling.

Wildlife

You’re in the Hayden Valley corridor, so bison and elk commonly wander through. Give wildlife plenty of space—at least 25 yards from bison/elk and 100 yards from bears/wolves—and be ready to yield the area if animals approach.

Logistics

• Parking: A small pullout/viewpoint sits at Sulphur Caldron; the larger Mud Volcano lot is just across the road, linked by a crosswalk/sidewalk.
• Services: No water or food here. Vault toilets are at the Mud Volcano parking area; for more reliable services, head to village hubs like Lake or Canyon.
• Surfaces: Stay on the designated walkway; thermal ground can be thin and unstable, and the water is near-boiling and highly acidic.

Is It Worth It?

If you’re nearby, absolutely—especially when combined with Mud Volcano/Dragon’s Mouth Spring. It’s not the park’s most colorful scene, but it’s one of the most chemically extreme, and that alone makes it memorable.

Best Time to Visit

There are no set hours for this roadside pullout. Fold it into your Mud Volcano stop or a Lake-to-Canyon drive. In summer, check current park alerts and road work before you go; construction and wildlife jams can affect timing.