Hmmm
Armillaria are also edible, really popular in Italy. They are one of the few parasitic fungi out there. Most higher fungi are saprophytic, meaning they grow on dead and decaying wood. Armillaria, however, will attack a living tree. Usually not a strong, healthy tree, but more often one which is in some way weakened. However, Armillaria are particularly fond of oak and I imagine they could establish in a perfectly healthy tree and go to work.
Armillaria (honey mushroom) grow in clusters, so JimmyQ's mushroom resembles Armillaria in color only.
I don't know jimmy's specimen. My expertise lies in fungal biology and commercial cultivation of edible species. There are thousands of species of mushrooms, and I only know about 50. As far as the biology of higher fungi, there are gross similarities across the board as far as lifecycle and what their purpose in life is.
The thing to do, JimmyQ, woould be to carefully excavate the base of the mushroom to see if it is attached to the root flare, or is it attached to a piece of wood under the soil, or is it growing out of the mulch or soil. Also, do other mushrooms of the same specie grow in a line outward from the tree (dead subterranian root)? Look up, are there limbs dying back on that side of the tree? Is the bark intact near where the mushroom grows, or will it peel off? Thunk the area around the trunk with a rubber mallet. Fungus-infested areas often have a more dull 'tone'. These are some clues as tothe interaction between the fungus and the tree.
From just your picture, my guess is that it is a terrestrial (ground-dwelling) specie that just happens to be located at the base of a tree.