Cap 2.0-6.0 cm in diameter, at first broadly-conic to campanulate, then convex, expanding to plano-convex, often with a low umbo; margin at first incurved, then decurved, striate; surface glabrous, lubricous when moist, brown to grey-brown, fading to pale-grey or buff, sometimes tinged yellowish when dry; context firm, whitish, unchanging, up to 5.0 mm thick at the disc; odor mild, (of yeast according to Smith); taste mild.
Gills adnate, adnexed, to subdecurrent, close when young, fairly well-spaced at maturity, pale-grey; lamellulae 3-4 seried.
Stipe up to 15.0 cm long, 1.5 cm thick, straight to curved, slightly enlarged at the base; surface glabrous at the apex, whitish to pale watery-grey, becoming pale-yellowish to buff in age; lower portion brownish, covered with a white tomentum; stipe base frequently fused with adjoining fruiting bodies; context cartilaginous, readily splitting, hollow at maturity, not exuding a colored juice when injured; partial veil absent.
Spores 5.5-7.0 x 3.0-3.5 µm, elliptical in face-view, inequilateral in profile, sometimes appearing bean-shaped, smooth, thin-walled, hilar appendage indistinct, amyloid; spore print white.
In cespitose clusters on downed wood and stumps of montane conifers; fruiting in the spring near melting snowbanks; common.
Mycena overholtsii is recognized as much by its conspicuous clustered fruitings on downed conifer wood as by its macroscopic features, a brownish, glabrous cap, and strongly tomentose stipe base. A collybioid stature and large size make confusion with other mycenas unlikely, but unrelated lignicolous mushrooms such as Strobiluris albipilatus and Pluteus petasatus bear a resemblance. Strobiluris albipilatus is differentiated by smaller size, a straw-yellow to tan-colored stipe and scattered, not clustered fruitings, while Pluteus petasatus is larger, rarely as clustered, has a squamulose cap disc, free gills, and pinkish spores.