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Sulphur Works, Lassen Volcanic National Park

Geologic Feature
Sulphur Works in June. – Leah Duran

The rotten egg odor of sulfur is the first thing I notice when I step out of the National Park Service vehicle. The sun is hot, the sky brilliant blue and cloudless. I greet the red fir tree next to the parking lot and stand in its shade while waiting for visitors to arrive. Twice per weekend, I lead a morning tour around Sulphur Works, the only geothermal feature in Lassen Volcanic National Park that is accessible from the main park road.

Lassen Volcanic National Park boasts three of the four geothermal features that exist: fumaroles (steam vents), boiling springs, and boiling mudpots. The primary attraction at Sulphur Works – a boiling mudpot five feet across – bubbles next to a sidewalk. Pillars of steam from fumaroles rise across the road. Clay minerals, formed when hot, acidic water percolates through volcanic rock, splash their vibrant palate of yellow, orange and red across the landscape.

When visitors stand next to the mudpot, they are standing in the middle of an ancient volcano called Mt. Tehama (also referred to as Brokeoff Volcano) that towered 11,000 feet high half a million years ago. About five miles below the ground lies a giant pool of magma. This magma – the same source that helped create Mt. Tehama – still heats the geothermal features today. Rainwater travels through the porous volcanic soil, mixes with magmatic chemicals, and is heated to steam, which causes the groundwater to boil. Microscopic organisms called Archaea live in the mudpot, and are being studied by scientists for their potential to cure genetic and infectious diseases.

A section of the earth’s crust began collapsing in 2006, and by 2008, the current mudpot visitors can see was formed. This dynamic area undergoes not only yearly, but seasonal changes; in October, the mudpot dries out. I show visitors a series of pictures recording these changes. The black and white photograph from 1936 garners the most reaction. Cars are parked next to the slope where the mudpot is today, and overnight cabins encircle the parking lot.

In 1865, Mathias Supan, an entrepreneur from Austria, started a sulfur mining operation for a variety of products, including medicinal ones such as “Supan’s baby colic.” As sulfur mining became less profitable, the Supan family appealed to the tourist crowd with mineral baths, a restaurant, and a souvenir shop. The National Park Service acquired Sulphur Works in 1952 – 33 years after Lassen was designated as a national park – through a condemnation suit filed by the U.S. Department of Justice that allowed the government to pay the Supan family a court-determined price for the area.

Visitors can view more geothermal features along the back side of Sulphur Works by climbing partway up the nearby Ridge Lakes trail. A black box measures the temperature of the mudpot (on average 180 degrees Fahrenheit) every 15 minutes. Scientists from Chico State University are conducting studies to gather information on what temperatures are normal for the area, as this restless landscape may well erupt again.

Through giving tours, I help illuminate some of the inner workings of Sulphur Works. If you take the time to immerse yourself in this active volcanic landscape, you will undoubtedly make your own unique discoveries.

Pet Friendly Notes

Pets on a leash are allowed along the sidewalks at Sulphur Works. Pets are not allowed on any park trails or in any park buildings. More information on the park’s policies regarding pets can be found here:

Recreational Opportunities

Recreational opportunities at Sulphur Works include walking, photography, ranger-led tours, and hiking along the nearby Ridge Lakes trail. In the winter, visitors can snowshoe or ski to Sulphur Works.


Seasons Accessible

Sulphur Works is accessible by car in the summer and by ski or snowshoe in the winter.


Admission into the park is $10 and is valid at any park entrance for seven days.

Nearby Places