This is a painted horse hide in the Sioux County Museum in Orange City, Iowa. It was labelled as the Battle of Twin Buttes. The writer on whose site I found this (https://blog.perspectivesjournal.org/2017/12/01/slim-buttes/) thinks it depicts the fight at Twin Buttes. Unfortunately, I have no idea about context or provenance, though I suspect the date is fairly late. Certainly interesting, though.
There's a photo of the hide on the museum's Facebook page: