there existed two main variants of the genre: the more whimsical, surrealist British psychedelia and the harder American West Coast "acid rock". While "acid rock" is sometimes deployed interchangeably with the term "psychedelic rock", it also refers more specifically to the heavier, harder, and more extreme ends of the genre.

The peak years of psychedelic rock were between 1967 and 1969, with milestone events including the 1967 Summer of Love and the 1969 Woodstock Festival,