The Sixmile Butte lava field, of Pleistocene age, consists of ten cinder cones between Black Butte and Black Crater. These cones erupted basaltic andesite, which was deposited prior to the glacial advance at Suttle Lake. The field encompasses about . Lava deposits from nearby Cache Mountain have a normal magnetic polarity, corresponding to an potassium-argon dating age of 0.9 ± 0.05 million years, suggesting they were produced during the Jaramillo normal polarity of the Matuyama period between 0.98 and 1.04 million years ago. There is a chain of Pleistocene cinder cones east of the butte that trends from northwest to southeast, with other Pleistocene cinder cones located to the south. There is also a mafic, well-preserved cinder cone above the Green Ridge fault zone, which produced a Pleistocene lava flow.