In our backyard below the peach trees, we found over a dozen large white mushrooms growing in the lawn. They were gorgeous and perfectly formed and must have formed overnight as I didn't see them yesterday. I was a little concerned that the dogs might want to chow down on them but they avoided them like the plague. We plucked them up to be sure.

Mushroomexpert.com helped to identify this as the Amanita thiersii of which edibility is unknown but likely poisonous.