From Wood and Kienle (1990) 
: "Falling Mountain and Mount Cerberus are the twin domes of pyroxene dacite (64% SiO2) that frame the entrance to Katmai Pass. They are similar in volume (each 0.25 cubic km), composition, lithology, and weathering. Although undated, they are thought to be of early Holocene age because their carapaces are degraded but not significantly glaciated. The two domes are compositionally similar (but not identical) to 1912 dacite. Together with the rhyolitic Novarupta dome, they define a 3-km-long line parallel to, but 4 km behind, the volcanic front."