Uncle John's Band
From the song of the same name by the Grateful Dead, and released on their 1970 album Workingman's Dead.
Most of the lyrics are a bit mystical, and don't concern the titular band. What can be determined is this band has a regular gig playing an estuary, where a river meets the ocean:
Come hear Uncle John's Band by the riverside,
Got some things to talk about, here beside the rising tide.
It may be a reference to John Cohen of real band The New Lost City Ramblers. A number of mystical-sounding phrases are references to NLCR song titles.