According to historians, when the explorers, Lewis and Clark, were passing by the bluffs near the site of the present town of Newcastle in Dixon County, they noted that one bluff seemed to be on fire. Some time later, fur trappers reported dense smoke and fire in the region.
Although "volcanic" activity was explained to be the simple decomposition of iron pyrite beds, when they came into contact with water, the Ionia Volcano was still viewed with much apprehension by early settlers in the area. In 1878, the Missouri River washed away the base of the bluff and, with it, all appearances of volcanic activity.
Today, there is an historical marker in Pfister Park in Newcastle, directing visitors to the site of the former volcano. Don't expect to see a volcano when you get there, however, the site is now a river bluff. From this location, the visitor can see three states: Nebraska, Iowa, and South Dakota.