On August 24, 1804, Clark explored a distinctive “180 or 190 feet high” bluff along the west side of the Missouri River. He wrote, “Those Bluffs appear to have been laterly on fire, and at this time is too hot for a man to bear his hand in the earth at any debth, gret appearance of Coal. An emence quantity of Cabalt or a Cristolised Substance which answers its discription is on the face of the Bluff.” Ordway further elaborated that the bluff “had a Sulpheras Smell”.

Following Lewis and Clark, later fur traders and travelers frequently noticed dense smoke and fire in this region. In 1839, French explorer J. N. Nicollet attempted to prove that these phenomena were not of vol­canic origin. He theorized that the decomposition of beds of iron pyrites in contact with water resulted in a heat capable of igniting other combustible materials. Still, by the late 1800s the bluff was known as the Ionia Volcano. It was named after the nearby town of Ionia, established in 1856. In 1878, a flooded Missouri River undermined the bluffs and a large section of the “volcano” fell into the river. The same flood heavily damaged the town of Ionia, which was later completely abandoned. By 1900, there was scientific consensus that the eruptions were due to the heat caused by the oxidation of damp pyritiferous and carbonaceous shale exposed by erosion.