This little mushroom is an Amanita phalloides, also known as the Death Cap. Although they're not native to North America, there are scads of them where I live in northern California.
Amanita phalloides are mycorrhizal, meaning that they grow in association with a plant. Both the plant and the fungus benefit from the relationship. A. phalloides appear to be especially enamored of oaks (Quercus sp.). No one knows for sure how they arrived in North America. Although they may have arrived on the shores of North America on imported cork oaks (Quercus suber) they're now found flourishing alongside our native oaks, especially live oaks.
I've seen and drawn many since I began noticing mushrooms three years ago. Until now, I couldn't imagine every mistaking A. phalloides for any other mushroom. This one fooled me, though. Those that I usually see are stocky, often quite large and have a metallic greenish-yellow cap with white veil remnants on them. This slender, delicate mushroom caught my eye and led me to believe that I'd found an Amanita I'd never seen before.
As I drove home, and mentally reviewed the mushroom's characteristics, I began to think that it might indeed be a Death Cap. When in doubt I always go to Mushroom Observer and that's where I confirmed the identification of this deadly little beauty.