View the spoiler for my guess at what I think it might be, but please first come to your own conclusion before looking at mine — I don't want to bias your guess.

They were found in mid-november in the Salish Coast region of Cascadia. They were growing out of woodchips composed of a mixture of western hemlock (majority), and western red cedar.

Side view of one full mature specimen:

A group with a sample of the substrate (the cap appears to be umbonate):

A closeup side view, and internal view of the stem (it appears to be hollow):

Cross section of the gills — they appear to be adnate, or sub-decurrent:

Underside of view of the gills:

Spore print (first on white background (the split is due to two halves), second on a black background):

Examples specimens once dried:

Examples of the colony, and the location/substrate in which it was growing:

Cross-posts:

• https://sh.itjust.works/post/28348065
• https://sh.itjust.works/post/28348066
• https://sh.itjust.works/post/28491127