Chroogomphus rutilus

This is a key to gilled mushrooms, that is, mushrooms having a definite cap with a fertile surface consisting of gills. The fruiting body usually also has a stem, although that may be lateral or absent (usually, then, the mushroom is growing from wood). You can use this key to identify mushrooms that you find.

Fruiting body containing fibers (usually in the stalk)

Spore print smoky-olive to black
Gills very decurrent, becoming smoky in age from developing spores
Cap typically slimy, or at least viscid
Under conifers only

Flesh (and gills, before they become colored by developing spores) colored: pinkish, yellow or orange
More likely to be umbonate

Cap up to 5" across; some shade (reddish, olive or orange) of ochre when young, darkening (sometimes quickly, as in the picture; sometimes more slowly) through a wide variety of colors to vinaceous at maturity
Stalk pale or dull orange to ochre, aging or staining vinaceous; often with black fibrils
Partial veil ochre; fibrillose, evanescent or leaving an annular zone that becomes blackened by trapped spores (traces of this on both larger mushrooms in the picture)

Chroogomphus rutilus     (Ja.C. Schaeffer: Fries) O. K. Miller