Cap 3.5-8.0 cm broad, convex, expanding to nearly plane; margin even to wavy, incurved when young, decurved in age; surface cream to buff-tan, overlaid with appressed fibrils which become yellowish-orange to orange-red with handling or age; context firm, cream-buff, up to 1.0 cm thick at the disc, yellowing slowly and erratically when cut; odor faint, somewhat pungent like that of raw potatoes; taste slightly unpleasant.
Gills adnate to adnexed, close, moderately broad, pallid to buff-brown when young, rusty-yellow in age, at maturity edges lighter than the faces; lamellulae up to 3-seried.
Stipe 5.0-8.0 cm long, 1.0-3.0 cm thick, solid, equal, ventricose, to clavate; surface of apex whitish, glabrous to sparsely fibrillose, lower portion pallid with scattered appressed fibrils, becoming brightly colored like the cap, i.e. yellowish-orange to reddish-orange; context of stipe base cream-colored when cut, turning bright-yellow, eventually orange, elsewhere slowly yellowing when injured; partial veil fibrillose, evanescent, leaving a zone of orange-colored fibrils high on the stipe.
Spores 6.0-7.5 x 3.5-5.0 µm, roughened, thin-walled, broadly ellipsoid in face view, conspicuously inequilateral in side view, hilar appendage not prominent; spore print rusty-brown.
Solitary to scattered in mixed hardwood-conifer woods; fruiting from late fall to mid-winter.
Undistinguished in youth with a pallid to cream-colored cap, this Cortinarius undergoes a transformation becoming flushed bright orange in age. Adding to its distinctiveness is a stipe base that turns bright yellow when cut or injured. Like many Cortinarius species, Cortinarius rubicundulus seldom fruits in numbers. It is most likely to be encountered along the coast from Sonoma County northward.