The region was active in the Pleistocene, with eruptions between about 650,000 and about 250,000 years ago from an explosively active complex known as the Tumalo volcanic center. This area features andesitic and mafic cinder cones such as Lava Butte, as well as rhyolite domes. Cinder cones accumulate from the airfall of many pyroclastic rock fragments of various sizes, while the viscous rhyolite domes extrude onto the surface like toothpaste.