An unexpected crop

During the night between Tues., Aug. 16 and Wed. Aug. 17 a mysterious crop arose in one section of my lawn.

It was a crop of mushrooms. Why? I do not know. They did not appear anywhere else in the garden.

Not being an expert mycologist, I was reluctant to eat them. They had the appearance of small portabellas but the underside was pink which made me suspicious.

Any one  know? I would appreciate knowing and I am sure others would too.