Hi ruauu2 - Very attractive mushrooms/photo. Very unlikely to be a Russula: Although I can't see the stipe and cap underside details required to be absolutely positive, the overall gestalt is not Russula-like. Also very few Russulas grow on wood and this wood does not look like it is a sufficiently rotted stage to qualify as Russula substrate. And Russulas will form groups but not true clusters. Generally it looks collybioid, possibly a Gymnopus.
I appreciate the details, Frog - I intend to be more deliberate about gathering clues in the field from now on. Going on your suggestion, it appears that this could be Gymnopus dryophilus?
