What spectacular and iconic horror paperback cover art of the 1970s! I haven't read Jeffrey Konvitz's bestselling novel The Sentinel (Ballantine, Jan 1976), but I did see its star-studded film adaptation, which featured one of the most vapid of leading ladies as well as actual deformed humans to recreate this stepback art! Heavens.
The paperback revels in then-classic horror imagery: creepy old priest, Charlie Manson-looking demonic hippie - I can totally see how this would appeal to someone scanning the drugstore racks - and then you open up the cover and you're accosted by a hellish vista of even more demonic hippies! That decade wore its fears and phobias pretty much on its sleeves.