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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I'm tempted to say Agrocybe, but they were very small and dried into almost nothing. Didn't seem quite right for Agrocybe