Cap 2.0-7.0 cm broad, convex, plano-convex to plano-depressed in age; margin at first incurved, then decurved to uplifted, even to wavy, sometimes remaining partially attached to the stipe; surface subviscid when moist, appressed radially- fibrillose to squamulose; scales dull brown to vinaceous-brown over an ochraceous background; context up to 5.0 mm thick, rapidly tapering to the margin, buff-yellow, unchanging to slowly pinkish-vinaceous; odor aromatic, like that of Suillus pungens; taste mild.
Pores large, often compound, irregular in shape, radially arranged (boletinoid) to sublamellate, mouths dotted with brownish glands; pores at first yellowish-buff, becoming ochre-colored in age, not bluing; tube layer up to 1.5 cm thick, contorted, i.e. not vertically oriented, subdecurrent to decurrent to the stipe.
Stipe 1.0-2.0 cm long, 0.5-1.0 cm thick, central to eccentric, slender, short relative to cap size, narrowed towards the base, growing from a copious white mycelium; surface of apex pale dull-yellow from the descending pore layer, elsewhere whitish with brown glandular dots; partial veil fibrillose, whitish, tinged vinaceous, leaving remnants on the cap margin and stipe apex.
Spores 7.0-10.0 x 3.5-4.0 µm, subfusoid in profile, elliptical in face-view, smooth, thin-walled, apiculus inconconspicuous, with one to several vacuoles; inamyloid; spore print not seen, "olivaceous" according to Snell and Dick.
Solitary to scattered under conifers, primarily Pinus contorta (lodgepole pine) along stream courses at higher elevations of the central and southern Sierra Nevada; fruiting after summer thunderstorms and in the early fall; locally common.
Named for its unusually large pores, this Suillus is also distinctive for its gastroid appearance, i.e. pores that are labyrinthoid, not vertically arranged, as well as a short, poorly developed stipe. Suillus riparius is similar but differs in its larger size, non-gastroid pore layer, and tendency to fruit near rotting wood at lower elevations with Pinus lambertiana (sugar pine) and Pinus ponderosa (yellow pine). Also bearing a resemblance is Suillus umbonatus which shares a preference for fruiting with lodgepole pine and is also annulate, but can be distinguished by a viscid veil and non-gastroid tubes.