East Butte is a 6,572-foot lava-dome summit of aphanitic rhyolite on Idaho’s Eastern Snake River Plain, formed about 600,000 years ago when sialic magma rose through surrounding basalt. Though not towering, it rises more than 1,200 feet above the plain within a mile, making it a striking landmark in a wide, open landscape. Together with Big Southern Butte, its line parent, it guided early explorers and pioneers crossing the region. The butte now stands on Idaho National Laboratory land, where access is restricted, although a road reaches the summit area and its radio towers. Its name is officially recognized by the United States Board on Geographic Names.