I believe it was the Long Beach Concert Band. Just the drummers (snare, tenor, and bass) were having a reunion. There were drummers in their 20's up to the 50's+ in age. They assembled on the walkway at the beach early one evening to have a impromptu jam session.
This is a fine image! Just one thought to make it (IMO, of course) even better. Look at it cropped just a tad on the right. Say just into the shoulder of the dominant person. There's some confusing stuff in the right border area that seems to be taking away from this very forceful image.
In any event, you were certainly at the right place at the right time and took advantage of an excellent scene.