Nice find! I agree with @sketch.and.jam that it looks like some relative of reishi mushroom (Ganoderma tsugae), but true reishi usually only grows on Eastern Hemlock trees (Tsuga canadensis). It may be either Ganoderma lucidum or Ganoderma curtisii depending on where you live in the world. Great find no matter what it is though. Thanks for sharing :)

Ganoderma curtisii: https://www.mushroomexpert.com/ganoderma_curtisii.html
Ganoderma lucidum:https://en.wikipedia.org/wiki/Ganoderma_lucidum & https://www.ncbi.nlm.nih.gov/books/NBK92757/