The Black Mass

The Black Mass was a horror-fantasy radio drama produced by Erik Bauersfeld, a leading American radio dramatist of the post-television era. The series aired on KPFA (Berkeley) and KPFK (Los Angeles) from 1963 to 1967, on an irregular schedule. Bauersfeld was the Director of Drama and Literature at KPFA from 1966 to 1991.
Bauersfeld's sound designer for most of the episodes was John Whiting, KPFA's production director. Their collaborations were later credited in a Ph.D. dissertation with "keeping radio drama alive in America in the 1960s." 
Music for the series was by several Bay Area composers, including KPFA's Music Director Charles Shere, a composer and music critic who later wrote books on American composers and also serves on the board of the Berkeley restaurant Chez Panisse.
Bauersfeld's "Black Mass" productions were an influence on writer-producer Thomas Lopez (ZBS), who noted, "In the 1960s, I was inspired by someone at KPFA in Berkeley, Eric Bauersfeld, who did a series called "The Black Mass", adaptations of H. P. Lovecraft and such. He helped me a lot. I consider Eric my mentor. He also did some fine Eugene O'Neill plays for radio."
Episodes.
Except as noted, these are in the Pacifica Radio Archives and on the Official "Black Mass" site:
The following are listed from KPFA, KPFK or KQED airchecks, not the Pacifica Archives:
"Great American Scream" - KPFK: