did the festival have a "program booklet" ?? that should have
complete listings, and newspaper adverts or reviews
usually listed many performers.

There are a number of recordings of Mariposa performances on LP
from 1975 and 1076.

a 2002 CD lists:
"Members of Swamperella
Lady Luscious (from Woman Ah Run Tings)
Nancy White
Bob Snider
Spirit Wind   
Dave Clarke (from Steel Rail)
Serena Ryder   
Jenny Whiteley
and more"

Thomas.