Lassen Peak is a 10,457-foot lava dome volcano in Northern California and the southernmost active volcano in the Cascade Range. Formed about 27,000 years ago through the flank of the older Mount Tehama, it quickly reached much of its present height and was later carved by glaciers, leaving a cirque and broad talus slopes. One of the largest lava domes on Earth, it is notable for heavy snowfall, lingering summit snow, and a dramatic eruption sequence from 1914 to 1917, including a major blast on May 22, 1915. Though dormant, it remains active beneath the surface and is closely monitored.