In 1915 the last California volcano erupted. Which mountain was it?

For 65 years, a peak in Northern California held the distinction of being the site of the most recent major volcanic eruption in the contiguous United States. This changed with Mount St. Helens in 1980, but the California record belongs to Lassen Peak. Its dramatic eruptive period began in May 1914 and culminated in a powerful explosion on May 22, 1915. This event sent a colossal column of ash and volcanic gas more than 30,000 feet into the sky, a spectacle visible from hundreds of miles away.

The 1915 eruption reshaped the surrounding landscape, creating an area of flattened trees and volcanic debris still known today as the Devastated Area. Ash from the blast fell as far east as Elko, Nevada, and pyroclastic flows and mudflows (called lahars) swept down the mountain's flanks. Today, the volcano is the centerpiece of Lassen Volcanic National Park, a region closely monitored by geologists. While it has been quiet for over a century, it is still considered an active, not extinct, volcano, serving as a powerful reminder of the dynamic geology of the Cascade Range.