The kids and I found this and then put cones on either side!!
Mushrooms are really amazing from the point of view of the speed of growth and the fact that their strength lies in pure hydraulics. Hitting the pavement with a hammer wont have any real effect, but some chitin and water and wow..
If any one is really interested there are some (quite heavy going) books by Stamets and Chilton, mainly on cultivation, but there is a lot on the ideal growing conditions and also non the diseases which affect fungi. for the serious myco-inclined they are a good read. You never know you might get into cultivation, I did - Shii take.
Thanks for your comments, we do find some great urban wild stuff and photograph it.