Loomis Museum, Volcanological museum in Manzanita Lake Area, California.

Loomis Museum is a one-story rectangular building of local volcanic rock in cut-face random ashlar coursing, about 25 by 60 feet, with small rear extensions making it T-shaped. It has prominent crenelated stepped parapets, a main entrance with sidelights and a fanlight under a bracketed shed roof, and green tile roofing. The interior is mainly a single large room.

Benjamin Franklin Loomis built this structure in 1927 to display his photographs of the 1915 eruptions of Lassen Peak. The museum was created as a record of one of the last major volcanic eruptions in the continental United States.

The museum was dedicated on July 4, 1927 as the Mae Loomis Memorial Museum, named for Luisa Mae Loomis, the Loomises' only child, who died in 1920. Its exhibits show Benjamin Franklin Loomis's photographs of the 1915 Lassen Peak eruptions, geological specimens and artifacts of local Native Americans. A Mather plaque hangs on the facade left of the entrance.

The seismograph station stands about 45 feet (14 m) northeast of the museum; its three large windows let visitors see the equipment inside. The museum and station are part of the Manzanita Lake Naturalist's Services Historic District, listed on June 23, 2006. The museum was renovated in 1994 and the seismograph building in 1995.

The building itself is constructed from different types of local volcanic rock, making it a kind of three-dimensional teaching tool about the region's geological variety. Visitors can identify the different rock types in the walls and structures, allowing them to explore geology firsthand.