You are looking at toadstools that have popped up in a circle pattern in the photograph. This circle of fungi is called a "faerie ring." Folklore says the ring is where faeries congregate to dance and socialize. The toadstools serve as umbrellas where faeries, elves, and pixies can be sheltered from sun and rain, and also be hidden from view of human eyes. It's magical!
This photo was taken in June 1992 at Cahokia Mounds in Illinois on the last day of our family vacation when driving home from New York to Iowa. In the photo, my oldest son who was eighteen years old gives perspective just how large this ring was. Indian mounds themselves are sacred, and to discover the faerie ring on this sacred land was very special.