I believe this may be an angel wing mushroom, Pleurocybella porrigens, but I'm not sure. It was no more than four inches across at the widest point and grew up very quickly. I spotted it at work one day where there was nothing just the day before.
Found under a bush in a shaded yard. The ground has a thick cover of old leaves and pieces of rotten wood from a nearby pile of firewood (which had very large turkey tail mushrooms on it). It was behind a shed next to a low stone wall with a pecan and bay laurel tree growing above it. Our pressure washer has made the area very wet.
Pictures taken with an iPhone 5.