The North and South Menan Buttes in southeastern Idaho are two of the world's largest volcanic tuff cones. The two cones, with four smaller associated cones, align along a north-northwest line and comprise the Menan Complex. The buttes rise about 800 feet (250 m) above the surrounding Snake River plain and are late Pleistocene in age, dating to approximately 10,000 YBP (Years Before Present). The South Menan Butte is currently in private hands, however North Menan Butte is publicly owned and has been designated as a National Natural Landmark and a Research Natural Area by the United States Congress. The US Bureau of Land Management designated the North Butte as an Area of Critical Environmental Concern (ACEC).