Three prominent buttes rise above a level plain of lava flows and windblown soils as relatively recent additions to Idaho’s landscape. East Butte, the farthest east, flowed up and cooled quickly about 600,000 years ago, while Big Southern Butte, south of here, emerged about 300,000 years ago. Although East Butte and Middle Butte have a similar appearance, they formed in different ways: East Butte became a dome of melted rock called rhyolite that rose through a volcanic fissure, while Middle Butte is a block of hard lava, or basalt, pushed up by volcanic activity from below.