I’m not 100% sure of this i.d. and need to get more photos and spore prints to confirm. If this is Corrugated-cap milky, then it’s a mushroom that likes oaks, and has latex inside that stains brown.
Size: Cap 4–20 cm diameter, stem 3-11 cm tall Family: Amanitaceae Habitat: Associates with oaks in eastern North America. Identifiers: Dark reddish cap, often coated with a very thin layer of white/gray felt when young. At maturity this disappears and the surfaces becomes corrugated. Fruits most often summer and fall.