The two cones, with four smaller associated cones, align along a north-northwest line and comprise the Menan Complex—and what most in the Yellowstone Teton Territory refer to as the Menan Buttes. 

The buttes rise about 800 feet above the surrounding Snake River plain and were formed during the late Pleistocene in age, dating to approximately 10,000 YBP (Years Before Present). 

The volcanoes forming the two major Menan Buttes were created when basaltic magma came into contact with a shallow aquifer or with the precursor of the modern Snake River—an unusul occurrence when molten magma met cold river water, and cooled so quickly that crsytals couldn’t form, and so the lava solidified into glass, called tachylyte.

In addition to their geological significance, the rhyolite domes of the ESRP are also culturally significant. Artifacts and archeological evidence suggest that humans have inhabited the ESRP since the end of the last ice age, ~13,000 years ago. 

Big Southern Butte was an important source of obsidian and artifacts sourced from there have been found throughout central and southern Idaho. More recently, travelers along the Goodale’s Cutoff spur of the Oregon trail in the mid-late 1800s and subsequent stagecoach and train lines utilized the freshwater springs along the base of Big Southern Butte.