I think these are Bolbitiaceae mushrooms. They appeared at night near our back deck after some heavy rain in mid-Feb (sorry, just posting these photos now). We had not noticed them during the day but when I looked out of the kitchen window that evening they were so obvious in the nocturnal twilight. The next day, with the sun up, their heads had started to dry out and turn black. I have seen them again in this area after rain but never in such numbers.