Most people won't disagree that the "Flower Power" movement associated with hippies, acid, and psychedelia didn't end with the 1960s but spilled over well into the new decade, with opinions varying from as early as 1970 with the Beatles' breakup and Jimmi Hendrix's death to as late as 1975 when Vietnam was finally over and progressive rock and acoustic singer-songwriters were stronger than ever. You couldn't deny the first Earth Day in 1970 as part of the Flower Power generation however as opposed to be geared toward the Me Generation typified by Disco, Arena Rock, and John Travolta/Farrah Fawcett wannabes.

With the end of this movement came a shift of fashion design from florals and muscle cars to products of a more geometrical shape (Think spherical disco balls, rectangular and boxy cars, etc.). Attitudes shifted from free love to explicity and personalism. When would you say this shift was complete?

I usually hear the movement more or less was dead by the time the US withdrew from the Vietnam War in 1973.

I think it was after 1974.

Maybe between 1973 and 1974.

1970 is definitely a core "Flower Power" year. Not only did you have the first Earth Day, as you mentioned, but you also had Nixon's expansion of the Vietnam War into Cambodia and Laos, something that sparked the massive campus protests that eventually led to the Kent State shootings, and the massive Student Strike that subsequently followed.

To me, 1972 is the last true Flower Power/Hippie year. After George McGovern was crushed by Richard Nixon in November of '72, and then Nixon ended the draft in January of '73, the whole movement died down pretty quickly. You could argue, as I've seen some do, that the Hippie era ended after Nixon resigned in 1974, but in my opinion it had already been dead for quite some time by that point.