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Hillside boiling mu... Roadside bubbling m... Hillside view 1 Hillside overlook 2

As in many hydrothermally active areas, the rocks at Sulphur Works in Lassen Volcanic National Park have been chemically altered into bright-colored clays. Sulfurous acid and sulfuric acid have broken down hard, gray-green andesite lavas into red, yellow and buff clays and iron oxides. Many visitors pass through Sulphur Works on their way north on State Route 89 and sense the rotten-egg smell (hydrogen sulfide) when they pass by a hot vent to the east of the road. Sulphur Works is said to be the volcanic center of the ancestral Mount Tehama. ( To Learn more about Sulpher Works visit the Mt Lassen National Park website:

Hydrothermal Area Safety For your safety, stay on established trails and boardwalks. Ground in hydrothermal areas can look solid but may actually be a thin crust hiding pools of acidic boiling water or mud. Traveling off-trail in these areas may result in severe injury. Visitors Have Been Injured When Traveling Off-Trail.

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