Equinox

Equinox is a 1970 American supernatural horror film directed by Jack Woods, and starring Edward Connell, Barbara Hewitt, Frank Bonner and Robin Christopher. Though uncredited, producer Dennis Muren also served as a second director. The film focuses on four young people picnicking in a California canyon, where they stumble upon an ancient book used to conjure demons; soon they unleash a plethora of evil creatures.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.