Brushy Butte is a small shield volcano in northern California, just east of Timbered Crater and south-southeast of the Medicine Lake Highlands near the Siskiyou-Shasta county line. Formed in a rifting area, it produced tholeiitic basalt, a dark lava rich in iron and magnesium with 45 to 53 percent silica. Although it remains poorly studied, its last known eruption is dated to the Pleistocene rather than the Holocene. Lava-flow landforms inside the volcano suggest eruptive activity lasted about 10 to 20 years, and its soil development and revegetation resemble those of the Hat Creek flow.