It's not as pointy as Shasta or as explosive as Long Valley, but Medicine Lake is one of the most geologically diverse volcanoes in California! While it keeps a (visually) low profile, Medicine Lake volcano covers around 2,200 square km (850 square miles) of northern California. Though shield-shaped, it's actually not a shield volcano like Hawai'i's Kilauea—eruptions there range in composition from massive basaltic flows to rhyolite domes and dacite tuffs. Its summit caldera formed not from a massive explosion, but from subsidence after repeated lava flow eruptions, which also built its rim higher! It's also a place of fire and ice: It's been covered by glaciers multiple times in its half-million-year history, but its lava flows have hundreds of lava tubes which carried molten rock as far as 30 kilometers (20+ miles) from erupting vents. Not to mention that some of those lava tubes now hold ice caves! 📷1: Looking out from Glass Mountain to the west, Medicine Lake and the Medicine Lake Highlands frame Mount Shasta in the distance. 📷2: The entrance to Skull Cave, a huge lava tube about 19 km (12 miles) north of the Medicine Lake caldera. 📷3: Glacier polish and scratches on andesite lavas of the north rim of the Medicine Lake caldera. Credit: J. Donnelly-Nolan, USGS California Volcano Observatory Weekly Update for October 19, 2026: All volcanoes in California were at normal background levels of activity for the last week. Earthquakes >M1 were observed at the Clear Lake Volcanic Field, Mono-Inyo Craters, Coso Volcanic Field, and Salton Buttes.