At rest for over 100 years in this location, the larger boulder here was once in the vent of Lassen Peak. A violent lahar, or mudflow, carried this 30-ton rock speeding down the slopes of Lassen Peak in a slurry of mud, earth, and rock. Visitors to the altered landscape reported that Hot Rock was hot to the touch even months after the eruption. The rock’s internal temperature is estimated to have been 1000°F when it came tumbling down Lassen Peak.

Benjamin F. Loomis captured photos of the 1915-1916 Lassen Peak eruption and this photo of Hot Rock. Can you imagine standing in this spot just after the eruption as Benjamin Loomis did? In a single day, this forested slope was made barren, with only broken trees to hint at what once was. Thick, boiling mud mixed with ash and scattered rocks almost instantly transformed this area to a barren, inhospitable landscape.

A century later, a forest reborn obscures many of the scattered rocks that tumbled down the slopes of Lassen Peak. Hot Rock serves a natural monument of the powerful forces of nature.