Astute observers, and wide-ranging park travelers, easily identified this week's Mystery Photo as the seismograph station at Lassen Volcanic National Park in northern California.
The station, officially known as the Loomis Seismograph Station, stands across from the Loomis Museum at Manzanita.
"Loomis" was Benjamin F. Loomis, who snapped some spectacular photos of Lassen Peak erupting in 1914 and against in 1915. Mr. Loomis built the station, which he "faced in volcanic rock, including random chunks of obsidian and pumice," in 1926 to monitor Mount Lassen.
The station was given to the National Park Service in 1929.