As Pleistocene glaciers retreated, basaltic cinder cone volcanoes formed south of Todd Lake right as Cayuse Crater was forming. Cayuse Crater, an unrelated postglacial volcano which formed 11,000 years ago, also sits on Broken Top's southern flank. It is made up of basaltic lava and scoria that erupted after Broken Top ceased activity, suggesting that it formed due to an underlying magma chamber closer to South Sister. Cayuse Crater also consists partly of yellow lapilli tuff and tuff breccia. It has a double rim, its southern wall having been breached by lava flows, with two additional smaller cones, about in elevation, to the northwest. More recent Holocene activity on the volcano's flanks constructed basaltic lava flows, cones, and ash that have become interbedded with moraine and material from outwash plains from the Neoglacial period.