The Fungus Fair runs this weekend at the Oakland Museum. The SF Mycological Society has tables and tables of mushrooms collected from the Bay Area and Sonoma Counties. If you're interested in learning how to ID them, you can learn some basics. There are displays on medicinal uses and um recreational uses. Spore prints, using mushrooms for dyes, microscopes to peer at lichen and mushrooms - they have it all. There's even a few cooking demos.
They had some vendors there with fresh shiitake and oyster mushrooms. Some sold those pre-treated kits so you can grow your own. (I did that once and happily gathered shiitakes for a few weeks from my 'log') I bought a can of corn smut - that will be interesting eating.
The Museum is open Sunday from Noon to 5 PM. Adult admission is $8.00. There were plenty of kids eagerly looking at the displays. Check the website for other admission prices. (And if you have a chance, look at their natural history area which is next to the mushroom exhibits - they are fantastic.)