[From here] "Indian Mound
About three and a half miles to the south of Gary, South Dakota, located at Cobb Creek, there is an Indian Mound. In 2008 it was inspected by a Tribal Chief and a Director of the Upper Sioux Agency. It was determined that it is a perfect example of a “Mound with a Tail” because of the way it is built. When you come to this area, make sure you get a chance to see this rare Native American attraction." [emphasis added]
(adding) gotta go look that up on Google.
Update: appears to refer to things like this: