Medicine Lake volcano forms a broad, seemingly nondescript highland, as viewed from any angle on the ground. Seen from an airplane, however, treeless lava flows are scattered across the surface of this potentially active volcanic edifice (see PHOTOGRAPHS). Lavas of Medicine Lake volcano (MLV), which range in composition from basalt through rhyolite, cover more than 2,000 km² east of the main axis of the Cascade Range in northern California. Across the Cascade Range axis to the west-southwest is Mount Shasta, its towering volcanic neighbor, whose stratocone shape contrasts with the broad shield shape of MLV. Hidden in the center of MLV is a 7 km by 12 km summit caldera in which nestles its namesake, Medicine Lake. The flanks of MLV, which are dotted with cinder cones, slope gently upward to the caldera rim, which reaches an elevation of nearly 8,000 ft (2,440 m). The maximum extent of lavas from this half-million-year-old volcano is about 80 km north-south by 45 km east-west. In postglacial time, 17 eruptions have added approximately 7.5 km³ to its total estimated volume of 600 km³, considered to be the largest by volume among Cascade Range volcanoes. The volcano has erupted nine times in the past 5,200 years, a rate more frequent than has been documented at all other Cascade volcanoes except Mount St. Helens.

This digital release contains the spatial database used to produce the geologic map published as U.S. Geological Survey Scientific Investigations Map 2927 and additional photographs. The main component of this digital release is a geologic map database prepared using ArcInfo GIS. This release also contains printable files for the geologic map (2 sheets) and accompanying descriptive pamphlet from Scientific Investigations Map 2927.