Backcountry Press

Lassen Geology

The Earth is not always quiet. An isolated region of northeast California offers a land of boiling springs, steaming sulfur vents, mud pots, and volcanoes. The boisterous geology of the southern Cascades is defined by Lassen Volcanic National Park. A complex and compelling geologic story is told in The Geology of the Lassen Country, a new book by R. Forrest Hopson and Michael A. Clynne.

June 14, 1914 phreatic eruption of Lassen Peak from near Manzanita Lake. Photograph by B.F. Loomis, courtesy of National Park Service.

While Lassen Country is not a formal name, it is used to describe both the national park and surrounding areas. The area encompasses a variety of fascinating geologic features set in a unique volcanic landscape. Did you know this is the site of California’s most recent volcanic eruption?

Volcanoes come in all shapes and sizes, and in the Lassen Country an amazing six volcano types are found. These include stratovolcanoes, volcanic domes, shield volcanoes, cinder cones, lava cones, and one explosion pit crater. In addition, Lassen Country contains the most active and spectacular hot spring fields in the Cascade Range. The mountains here feature crystal clear lakes and streams, forested mountain slopes, and wide range of plant and animal life.


Geologizing in a volcanic country is most delightful; besides the interest attached to itself, it leads you into the most beautiful and retired spots.

Charles Darwin

The book explores the geology and geologic evolution of the area, providing an up-to-date source of information specific to Lassen Country. This is all based on Michael Clynne’s life work. He has been piecing together the geologic story of the Lassen Country for over 30 years.

“Recent work by the U.S. Geological Survey has refined and built on previous geologic interpretations of the Lassen Country. This book is exciting to me because it makes the story accessible to everyone,” says co-author Michael A. Clynne.

Named for Kendall Vanhook Bumpass, a Lassen Country settler and prospector from the mid-1800s, Bumpass Hell encompasses 16 acres and contains approximately 75 boiling springs, superheated fumaroles, and mud pots. Photo by R. Forrest Hopson.

Forrest Hopson, the book’s other author, has been passionate about the Lassen Country for years and as a geologist since the 1980s.    

“This book is important because it offers an up-to-date synopsis of the geology of Lassen Volcanic National Park. The book explains how Lassen Peak is part of a long-lived magmatic system, called the Lassen Volcanic Center, where volcanism has produced a caldera, stratovolcano, and then a domefield that includes Lassen Peak” says co-author R. Forrest Hopson.

In addition to geology, the book offers cultural and historical notes about the region, a mile by mile geologic tour through Lassen Volcanic National Park to Old Station, and eight detailed hikes to get out and explore the amazing regional geology of Lassen Country.

The companion website offers supplemental materials and more details about the book. Get out this summer and explore the volcanic country in our own backyard.

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