This obelisk is a monument to the victims of the last Indian attack on white settlers in Iowa, which occurred in Spirit Lake, Iowa in 1857. There is also a cabin originally occupied by one of the survivors of the attack, who was held until ransomed. The woman, Abbie Gardner, also wrote about her experiences and operated her cabin as a tourist site.

State Monument Arnolds Park, Iowa Indian Massacre 1857
The monument is nearby the cabin where Abbie Gardner lived before and after her abduction. This picture likely dates from the 1940s.
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