We gave up on grass for much of our front yard after a disastrously hot and dry summer last year. (I couldn't morally live with the idea of soaking the yard with enough water to keep the grass alive, especially as I watched the primary area reservoir sink lower and lower.) So the problem parts of the yard are now covered in a few inches of dark mulch, with some rocks and native drought-tolerant shrubs, succulents, etc. Looks a little goofy but I'm happy with it for the most part.
Anyway it's been a lot wetter so far this year. Over the past couple of days we've seen a burst of mushroom activity. There are lots of them, almost uniformly across the shadier part of the area. Now to me, ignorant though I am, that means that there's some really happy fungus working over the bottom layer of the mulch, which is probably a really great thing for the soil (which still has to keep some 20yo live oak trees alive). I figure it's a good thing to leave them alone, and I already plan to add some more mulch pretty soon and turn it over to some extent.
The things are kind-of freaking my wife out however, and she's worried that they might actually be bad for the trees.
I can't say that I've seen this specific type of mushroom before, but then I've never had any of that particular kind of mulch in my yard and I figure the spores were there when it showed up in the truck last fall.