Sulphur Works

As in many hydrothermally active areas, the rocks at Sulphur Works and Little Hot Springs Valley 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.