After reviewing all the descriptions on record, the specimens with a brown to blackish cap are suspected to be Phylloporus arenicola. Red caps are Phylloporus rhodoxanthus. The original description of Phylloporus arenicola by Smith and Trappe (Mycologia 64: 1138-1153) says non-bluing and this has led to confusion over the northern California species. After making at least 10 collections, it is accurate to say the bluing is slow, slight and fades within minutes to yellow again. But the gills do blue when bruised in fresh specimens.
Cap: 1.5-4.5 cm; more or less flat, sometimes becoming depressed; dry; fairly smooth, or finely velvety; olive to olive brown or yellowish brown.
Gills: Attached to the stem but not running down it significantly and often pulling away from it in age; distant or nearly so; yellow to golden yellow; not bruising; thick.
Stem: 4-6 cm long; up to almost 1 cm thick; tapered downward; yellowish, with reddish and brownish stains or hairs.
Flesh: Pale yellow; not staining when exposed.
Taste: Mild; odor not distinctive.
Chemical Reactions: Cap surface immediately purplish gray with ammonia, then dark red. Iron salts weakly olive on flesh.
Spore Print: Not recorded; presumably yellowish to brownish yellow.
Microscopic Features: Spores 9-12 × 4-5 µ; smooth; long-elliptical to spindle-shaped; weakly dextrinoid.