This is a Fairy Ring of Shaggy Parasol mushrooms (Chlorophyllum rhacodes), also known as a fairy circle, elf circle, elf ring or pixie ring. It is a naturally occurring phenomenon.

FungiBasidiomycotaAgaricomycetesAgaricalesAgaricaceaeChlorophyllum rhacodes complexShaggy ParasolLandscape OrientationHorizontal OrientationNatural Background