Black Butte is a cluster of overlapping dacite lava domes in a butte, a parasitic satellite cone of Mount Shasta. . The highway crosses a 3,912 ft pass, Black Butte Summit, at the western base of the lava domes. The lava domes were extruded at the foot of the cone of Shastina following the period of its major eruptions about 9,000–10,000 years ago. |