Book excerpt: Psychedelic rock began in 1965 and was popular until around 1970. Its most important centres were San Francisco, the city of its origin, and London. One of its chief features was the attempt to translate into musical terms the effects of hallucinogenic drugs, especially LSD, which had become available in artistic circles in the early 1960s and was legal until 1966. San Francisco psychedelic music took its ideology from the folk music revival of the 1950s, which many of its most important practitioners had participated in, including Jerry Garcia of the Grateful Dead, Janis Joplin of Big Brother and the Holding Company, and members of the Jefferson Airplane. The catalyst for the folk revival musicians to adopt the rock band format was the British Invasion, which began in 1964 with the arrival in America of the Beatles. Psychedelic music is examined in relation to an original, seven-stage model of style evolution that is developed in the thesis. It looks beyond the heyday of the music, tracing the legacy of its decline and eventual revival in the present. The thesis offers detailed musical analyses that identify key structures, or matrices, in the evolution of the style. Much of the contextual evidence derives from original field work involving interviews with musicians and industry representatives who were part of the San Francisco scene.