Spore and pleurocystidia 1000X Melzers micrograph by Fred Rhoades.
Found on sagebrush steppe. Solitary. Spores (11.9 - 14.0) x (5.3 - 6.4) elliptic to navicular (boat shaped). Last 3 pictures/microscopy by @joemat
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Taste: mild
I'm tempted to say Agrocybe, but they were very small and dried into almost nothing. Didn't seem quite right for Agrocybe
In Tule Lake peatland under Populus tremuloides, Vaccinium uliginosum. Large, stocky.