From mushroomfarm..com
Gymnopus dryophilus name proposed on MO
"This is probably one of the most variable mushrooms
that you can find out in the woods in terms of color.
It is also one of the most common mushrooms.
The color of the cap can range from red to ochre brown to tan to yellow."
"You will likely need a microscope to separate out the closest lookalike -
Gymnopus brunneolus.
It has chestnut brown cap and short, stubby, cheiliocystidia.
Rhodocollybia butyracea has serrated gills.
Gymnopus acervatus usually grows in dense clusters.
Gymnopus subsulphereus has yellow gills and a yellowish cap.
Gymnopus earleae has yellow gills and a darker colored cap.
Marasmius strictipes has a yellow cap with a white stalk."