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U.S. Geological Survey Scientific Investigations Map 2927

Geologic Map of Medicine Lake Volcano, Northern California

By Julie M. Donnelly-Nolan


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. Lavas of Medicine Lake volcano, 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 Medicine Lake volcano. Hidden in the center of Medicine Lake volcano is a 7 km by 12 km summit caldera in which nestles its namesake, Medicine Lake. The flanks of Medicine Lake volcano, 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, and it is considered to be the largest by volume among volcanoes of the Cascades arc. The volcano has erupted nine times in the past 5,200 years, a rate more frequent than has been documented at all other Cascades arc volcanoes except Mount St. Helens.

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Last modified August 25, 2011
First posted February 28, 2011

Files for Viewing and Plotting

Data to accompany Scientific Investigations Map 2927

By David W. Ramsey, Tracey J. Felger, Ellen Lougee, Peggy E. Bruggman, and Julie M. Donnelly-Nolan

  • Database site. (112 MB total)
  • These pages contain the spatial database used to produce the geologic map and additional photographs. The main component of this site is a geologic map database prepared using ArcInfo GIS. Also included are links to chemical analyses for more than 600 pre-Holocene rocks collected at or near Medicine Lake volcano from U.S. Geological Survey Open-File Report 2008-1094.

  • This report is also available in print with a CD-ROM from:

    USGS Information Services, Box 25286,
    Federal Center, Denver, CO 80225
    telephone: 888 ASK-USGS; e-mail:
Contact Information
Volcano Science Center - Menlo Park
U.S. Geological Survey
345 Middlefield Road, MS 910
Menlo Park, CA 94025

Part of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Donnelly-Nolan, J.M., 2010, Geologic map of Medicine Lake volcano, northern California: U.S. Geological Survey Scientific Investigations Map 2927, pamphlet 48 p., 2 sheets, scale 1:50,000,



Previous Geologic Work

Geologic and Tectonic Setting

Pre-MLV Volcanic Activity

Eruptive History of MLV

The Caldera

Glacial History

Hazards, Resources, and Recreation


Introduction to Description of Map Units

Description of Map Units

References Cited

Sheet 1

Sheet 2

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