Howlin' Wolf came to town for several dates at the Fillmore in mid-April of 1967. The bills were diverse, as Bill Graham's often were in those days. April 15 was the second of three nights for Wolf and the openers.
The Loading Zone were a local act out of the East Bay. Their primary claim to fame was vocalist Linda Tillery, but she hadn't joined the band in 1967, so I have no idea what they sounded like. Perhaps this comes closest, an instrumental from their first album that I admit is the only song of theirs I recall from back in the day.
Country Joe and the Fish were also from Berkeley, and their subsequent fame surpasses that of the Loading Zone. While their first album, Electric Music for the Mind and Body, wouldn't be released for another month, they were known in the area for their two EP releases associated with the underground magazine Rag Baby.
Joe's mother Florence was a notable figure around Berkeley for many years, known for her radical politics and time served on various Berkeley city government positions.
It's not clear how the great Howlin' Wolf fits into this bill, except that's how Bill Graham did things back then. Wolf, a titan in music history, was enjoying new attention in the 60s thanks in part to the British bands who revered him (The Rolling Stones only agreed to appear on the TV show Shindig! after Howlin' Wolf was added to the episode). That's James Burton on guitar and Billy Preston on piano.