The cap ranges from 8–30 cm (3–12 in) across, is convex to flat,[1] and is bright yellow-orange in younger specimens and orange-brown or reddish brown in older ones, with a dry scaly surface.

[1] The frail ring is dusted with rusty orange spores, and the gill attachment to the stem is adnate to sub-decurrent.

Unlike psychoactive relatives in the Psilocybe genus, G. junonius lacks psilocybin and does not stain blue, but smaller specimens occasionally exhibit bruising.

These include Gymnopilus ventricosus on the west coast and G. luteus and G. subspectabilis in the midwest and east.

[6] This mushroom contains bis-noryangonin and hispidin, which are structurally related to alpha-pyrones found in kava.