Peter ,Paul & Mary's material is alive and well , but I guess the turning point / decline of folk-civilization was the folk-Pop-izations of "The Mama's and the Papa's" which , I'm sure , will wrinkle a few noses here , but their harmonies are still classic and "Creek Alley " as well-written a folk song ,albeit California-style ,as any written in capturing its *time* and it is still predominantly the vocal harmonies which can be supported by a single guitar as any P.P&M tune.