Medicine Lake Caldera 13. Aerial view west across Medicine Lake toward Mount Shasta, about 55 km away. In the middle ground is the treeless late Holocene rhyolite flow of Little Glass Mountain, part of a fissure rhyolite eruption which took place about 1,000 years ago (map unit rlg). Medicine Lake lies within the central 7 by 12 km caldera of Medicine Lake volcano. Southern end of 5,200-year-old Medicine Lake Glass Flow (map unit dm) can be seen on right. Photograph by Julie M. Donnelly-Nolan.