CAP 6–15 cm across, rounded to convex when young, expanding to broadly convex to plane or wavy. Margin down-curved at first, becoming wavy and slightly uplifted in age. Surface dry to slightly viscid when wet, covered with radiating streaks of appressed fibrils. Color highly variable. Bluish in the button stage, becoming bluish purple and developing dark brown streaks. As it ages, the purple tones usually darken to dark grayish brown or purplish brown. GILLS broadly to narrowly attached, often with a distinct notch, close to crowded, broad. Bluish to bluish violet at first, becoming lilac-gray and eventually darkening to deep lilac gray or gray-brown. Staining vinaceous red when damaged. STIPE 6–15 (18) cm long 1–2.5 cm thick at the apex, club-shaped or swollen with an elon- gated bulbous base, 1.5–4.5 cm thick. Surface dry, covered with silky fibrils that become matted in age. Bluish lilac to pale violet at first, fading to gray and then darkening to dingy gray to grayish lilac and developing dingy brown color from the base up. Staining bright violet when handled, these stains slowly turn vinaceous red and then deep purple. CORTINA leaving an annular zone of lilac fibrils on the stipe, becoming grayish and then rusty brown from the spores. FLESH thick, firm, fleshy. Bluish lilac at first, fading to grayish lilac, staining red to vinaceous red, especially in the stipe base. ODOR indistinct. TASTE indistinct to slightly bitter. KOH No reaction. SPORE DEPOSIT rusty brown. MICROSCOPY: Spores (8.5) 9–11.5 × 5–7 (7.5) μm ellipsoid to amygdaliform, distinctly roughened. Basidia (25) 35–50 × 8–11 (13) μm, 4-spored, clavate to broadly clavate, colorless to light yellow- brown. Pleurocystidia and cheilocystidia absent. Clamp connections present.
ECOLOGY: Ectomycorrhizal with conifers, likely with Abies in the California mountains. Most known sites are in old-growth forest, but it is unknown whether this species is restricted to such habitats. Fruiting in late summer and fall.
SIMILAR SPECIES: Cortinarius occidentalis (=C. mutabilis) has brighter purple colors, somewhat smaller fruit bodies, and stains purple on all damaged parts. Taxa in the Cortinarius purpurascens group typically have duller olive-tan or brown caps, and stain purplish on the gills and stipe. Cortinarius violaceus has a coarsely velvety cap and is entirely deep royal purple (to nearly blackish purple) in color.