[3] Lassen Volcanic National Park is one of the few areas in the world where all four types of volcanoes can be found: plug dome, shield, cinder cone, and stratovolcano.

[5] The area surrounding Lassen Peak is still active with boiling mud pots, fumaroles, and hot springs.

[8] Nobles Emigrant Trail was later cut through the park area and passed Cinder Cone and the Fantastic Lava Beds.

Inconsistent newspaper accounts reported by witnesses from 1850 to 1851 described seeing "fire thrown to a terrible height" and "burning lava running down the sides" in the area of Cinder Cone.

After the 1980 eruption of Mount St. Helens, the United States Geological Survey (USGS) began reassessing the potential risk of other active volcanic areas in the Cascade Range.

[citation needed] In October 1972, a portion of the park was designated as Lassen Volcanic Wilderness by the US Congress (Public Law 92-511).

The management plan of 2003 adds that, "The wilderness experience offers a moderate to high degree of challenge and adventure.

"[10] In 1974, the National Park Service took the advice of the USGS and closed the visitor center and accommodations at Manzanita Lake.

However, a campground, store, and museum dedicated to Benjamin F. Loomis stands near Manzanita Lake, welcoming visitors who enter the park from the northwest entrance.

Monitoring of the Lassen area includes periodic measurements of ground deformation and volcanic-gas emissions and continuous transmission of data from a local network of nine seismometers to USGS offices in Menlo Park, California.

[11] Should indications of a significant increase in volcanic activity be detected, the USGS will immediately deploy scientists and specially designed portable monitoring instruments to evaluate the threat.

In addition, the National Park Service (NPS) has developed an emergency response plan that would be activated to protect the public in the event of an impending eruption.

Lassen Peak is made of dacite,[20] an igneous rock, and is one of the world's largest plug dome volcanoes.

The 10,457 ft (3,187 m) tall volcano sits on the north-east flank of the remains of Mount Tehama, a stratovolcano that was a thousand feet (305 m) higher than Lassen and 11 to 15 mi (18 to 24 km) wide at its base.

[8] After emptying its throat and partially doing the same to its magma chamber in a series of eruptions, Tehama either collapsed into itself and formed a two-mile (3.2 km) wide caldera in the late Pleistocene or was simply eroded away with the help of acidic vapors that loosened and broke the rock, which was later carried away by glaciers.

According to the United States Department of Agriculture, the Plant Hardiness zone at Kohm Yah-mah-nee Visitor Center at 6,736 ft (2,053 m) elevation is 6b with an average annual extreme minimum temperature of −0.2 °F (−17.9 °C).

In addition, Lake Helen gets more average snow accumulation than any other recording station located near a volcano in the Cascade range, with a maximum of 178 in (450 cm).

From 8,000 feet to treeline, plants are fewer in overall number with exposed patches of bare ground providing a harsh environment.

[34] Areas such as Reflection Lake attract waterfowl, including Canada geese, great blue heron, snowy egret, and kingfisher.

[35] Lassen Volcanic Park is home to the Sierra Nevada red fox in particular, one of the rarest mammals in California.

[38] In 2024, a pack consisting of a breeding pair and at least one offspring was reported within Lassen Volcanic Park by the California Department of Fish and Wildlife.

[39] In the Cenozoic, uplifting and westward tilting of the Sierra Nevada along with extensive volcanism generated huge lahars (volcanic-derived mud flows) in the Pliocene which became the Tuscan Formation.

Another group of andesite lava flows called the Flatiron, erupted during this time and covered the southwestern part of the park's area.

Approximately 350,000 years ago its cone collapsed into itself and formed a two-mile (3.2 km) wide caldera after it emptied its throat and partially did the same to its magma chamber in a series of eruptions.

During glacial periods (ice ages) of the present Wisconsinan glaciation, glaciers have modified and helped to erode the older volcanoes in the park, including the remains of Tehama.

As the lava dome pushed its way up, it shattered overlaying rock, which formed a blanket of talus around the emerging volcano.

Lassen Peak has also been partially eroded by Ice Age glaciers, at least one of which extended as much as 7 mi (11 km) from the volcano itself.

Phreatic (steam explosion) eruptions, dacite and andesite lava flows and cinder cone formation have persisted into modern times.