The Bay Bolete is a medium-sized mushroom with a convex to flat cap, ranging from 5-15 cm in diameter, featuring a smooth, slightly sticky surface when moist. The cap color varies from chestnut brown to dark brown, often with a reddish hue, while the underside reveals a sponge-like layer of small, angular pores that are yellow to olive in color. The stem is stout, typically 4-12 cm tall and 1-3 cm thick, with a pale yellow to brownish color and a fine, net-like pattern near the top. The flesh is white to pale yellow, firm, and does not change color when cut or bruised.