fairy ring

I was wondering why the the grass is brown in between the lines of the ring, so I looked up this mushroom in the book Mushrooms Demystified by David Arora. Very interesting...here is a quote from the book. "...its presence can be detected even when it isn't fruiting - just look for 'fairy rings' (patches of brown grass rimmed by a lush zone of darker green grass). The living mycelium on the periphery of the ring stimulates the grass to grow, while the dried up mycelial matter within the circle inhibits growth." Also supposed to be delicious, but I'm not going to try it unless I have an expert ID it.