Medicine Lake Volcano is a large shield volcano in northeastern California about 30 miles (50 km) northeast of Mount Shasta. The volcano is located in a zone of east-west crustal extension east of the main axis of the Cascade Volcanic Arc and the Cascade Range. The 0.6-mile (1 km) thick shield is 22 miles (35 km) from east to west and 28 to 31 miles (45 to 50 km) from north to south, and covers more than 770 square miles (2,000 km2). The underlying rock has downwarped by 0.3 miles (0.5 km) under the center of the volcano. The volcano is primarily composed of basalt and basaltic andesite lava flows, and has a 4.3-by-7.5-mile (7 by 12 km) caldera at the center.