Did you see anything? - なんじゃろ？

近くに公園がありまして、仕事へ向かう時に通ったりするのですがで、昨日ここで見つけた、芝生に出来た模様。。。一体なんじゃろ？

There is a field near where I live - I sometime walk thorough to go to work. Yesterday, there was this strange pattern on the grass....What is it?