Cap 3.5-9.0 cm broad, broadly conic, expanding to near plane in age; margin at first incurved, wavy, sometimes splitting and raised at maturity; surface fibrillose-squamulose; dark brownish-black to dull, dark, greyish-purple, fading to medium grey-brown; context relatively thick at the disc, thin at the margin, greyish-brown just below the cuticle, pallid elsewhere, at times discoloring dingy vinaceous-grey; odor and taste farinaceous.
Gills notched, moderately broad, close, relatively thick, at first pale grey, darkening to light grey-brown.
Stipe 4-8 cm long, 1.5-3 cm thick, equal to enlarged at the base, stuffed/fibrous; surface of greyish to brownish fibrils over a pallid background, frequently with yellowish to orange-brown discolorations at base; partial veil absent.
Spores 7.5-9.0 x 5-6 microns, elliptical, smooth, nonamyloid; spore print whitish.
Fruiting singly or in small groups in conifer woods; appearing from late fall to mid-winter.
Until recently, the genus Tricholoma in general and grey-brown Tricholomas in particular were poorly known in the California. Fortunately, Kris Shanks's monograph of California Tricholomas has made it possible to sort out the various species. Among the easiest to distinguish is Tricholoma atroviolaceum by virtue of a dry, dark grey-brown, fibrillose-squamulose cap, usually with violet tones when young, and a stipe with yellowish to tawny-brown stains at the base in age. Other similarly colored Tricholomas that may be encountered include Tricholoma luteomaculosum, with a dry, fibrillose (not squamulose) greyish-brown cap, the latter sometimes with a yellowish-brown disc; Tricholoma virgatum, with a dry, streaked (not fibrillose), dark-grey, umbonate cap; Tricholoma portentosum, with a viscid, streaked, dark-grey cap, sometimes developing yellow tints in the cap and stipe, and Tricholoma griseoviolaceum with a streaked, grey-violet, viscid cap, but not yellowish in either the cap or stipe. Finally, unlikely to be confused with any of the above species because of its small size is Tricholoma myomyces var. cystidiotum, which has a dry fibrillose-sqamulose grey cap, and a grey fibrillose veil.