These are the Mima Mounds, a strange natural formation that has had many phenomenological explanations attributed to them. They exist in places all over the United States. What ever the reasons, I can tell you that when I drove down to see them for myself, I had no radio access in the area around the mounds. Couldn't tune in any stations. In life (called Real Life I suppose), we know what it's like when the radio frequencies don't tune in. Everyone else seems to be smiling and nodding to a broadcast that seems important, but we can't hear it.