The stalk begins white, but injuries or wear and tear discolor it and it discolors brown, like the rest of the mushroom.
It's common in oak woods, summer to fall, in the eastern half of North America.
It is most likely poisonous (possibly deadly), and it resembles other amanitas, such as nonpoisonous blusher, which has a stalk that tapers into a club at the end, rather than a bulb, and bruises reddish instead of brownish.
There's also a common subspecies of the cleft-foot amanita that's identical to the variety described above in every way, except that it's white.