The creation of Lassen Volcanic National Park began 700 million years ago.

Lassen Peak was an active volcano over 27,000 years ago. However, in May 1914,  volcanic eruptions took place that would last the next three years. First, a relatively mild explosion created a small crater at the summit of Lassen’s peak, but the subsequent events truly shaped the landscape. Since California was experiencing large amounts of snow at this time, the lava melted the snow, and instead of sending an avalanche, it melted the snow and sent a mudslide of volcanic material instead. This turned into flooding. Two days later came the biggest eruption of this series, shaping the deeper of two craters in the Lassen Peak. Once again, this triggered mudslides and flooding, which caused pumice and volcanic ash to be deposited, and ash to fall from the sky.

More recently, volcanic eruptions that are better described as lava floods began along eastern Oregon and Washington, adding to the volcanic rock deposition. As volcanoes in the area continue to erupt, large boulders and rocks are redistributed throughout the area, as seen in the 1915 volcanic event.