Yesterday, in the Redwood forest, I saw a couple of mushrooms that appeared fairly big compared to other white ones I've seen that may have resembled them. Have no idea what they are. The large one was about 6" in diameter. One of the bigger white capped mushrooms I've seen with a dome shaped cap. Maybe it will flatten in time.
I wonder if they are Pine Mushrooms? If so you may find a local buyer set up camp somewhere paying good money this year. My friend called yesterday saying he's getting $38/lb on Vancouver Island this fall. But.. I don't really know my mushrooms, they just kinda look like what I've seen from my friends annual mushroom picking trips, pictures.
I vote for Agaricus augustus (the Prince agaricus) as well. I don't have any scientific tests involving sticks to confirm the identity of this one, but it should have a brown spore print. ;)
The small one might still be in good shape when I get by there again in another week or so, if another doesn't pop up next to them. Maybe I can use a rubber band to hold a paper underneath to check the spore print. I usually try to avoid damaging the mushrooms in the redwoods, so other visitors can see them as well, if the redwoods don't take all their attention. About a third of the visitors I've met, mentioned that they are photographing the fungi they see.