- Mount St. Helens National Volcanic Monument is a U.S. National Monument that includes the area around Mount St. Helens in Cowlitz, Lewis, and Skamania Counties, Washington. It was established by Congress on August 27, 1982, following the 1980 eruption. The 110,000 acre (445 km2) National Volcanic Monument was set aside for research, recreation, and education. Inside the monument, the environment is left to respond naturally to the disturbance. It was the third national monument to be managed by the U.S. Forest Service and is part of the Gifford Pinchot National Forest.