Last fall an old valley oak (Quercus lobata) was cut down in this spot. Yesterday, I saw these interesting fungi fruiting where the tree used to be. As far as I can tell the spores are dispersed when the "skin" on top of the pileus splits or bursts, or when it just falls off, revealing the spores. The specimen pictured is 13 cm tall and the pileus is 5.1 cm across. It smells like grocery store mushrooms and produced no staining when handled.