My sister Amy commented on the previous Moody Blues post, which I cross-posted to Facebook,"Very 60's". Well, yes. A Question of Balance was released in 1970, but no one would deny that it was a "'60's" album.
So when did the '60's end? I think that the '60's are elastic, as is the Boomers cohort. But if I had to name a year, two years come to mind.
In 1973 the military draft ended, marking the end of mass opposition to the war in Vietnam. You could see this as the end of the '60's and the beginning of the Disco '70's. For American society as a whole, I would go with 1973 as the end of the '60's
Alternatively, at the end of 1980, Ronald Reagan defeated Jimmy Carter in the Presidential Election, and John Lennon was murdered. For "core" counterculture types, this is the more accurate date. The civil-rights/anti-war "Movement" had splintered into niche causes: post-Mao Maoism, Lesbian-Feminist Separatism, pre-AIDS "Gay Liberation", White Rastafarianism, and many other flavors; an efflorescence of decay. This was really when the scene in Tallahassee dissolved. It was SO over. Lots of people left for the West Coast, Seattle in particular, Ecotopia.
This was when I said Good-bye to All That.
Postscript, August 28, 2011
This post has gotten a lot of hits since I wrote it, so I feel I ought to mention a new book by David Browne, Fire and Rain: The Beatles, Simon and Garfunkel, James Taylor, CSNY, and the Lost Story of 1970. Browne argues that the '70's began, and the '60's ended, in 1970, a bold assertion. You can sample some reviews here.
I think it is a matter of perspective. My experience of the Sixties was in Florida, a cultural backwater. I didn't actually meet any hippies until 1969 at my high school.. It is hard to describe how difficult it was to find out about the "Counterculture" in those days. Progressive Rock could only be heard on the new, non-commercial radio station, FM 107. I recall endlessly poring over The Whole Earth Catalog, which was a sort of directory of hippie thought.
This was not the case in New York, Los Angeles or London.