My
theory is that
Valley Girl patois at any given time is keyed to the
speech habits of 14 year old
girls in the
San Fernando Valley, and that the
speech habits of those 14 year old girls are
keyed to the
recreational drugs that are currently in
vogue.
For example, I was 14 (early 70's), the fashionable drugs were slow drugs - quaaludes and marijuana. In fact, Valley Girl patois pretty much consisted of the expression, "Oh, wow, man."
When Moon Unit Zappa raised the nation's awareness of Valley Girl culture (early 80's), the fashionable drugs were fast - speed and cocaine. Thus, in the early 70's, Valley Girl speech patterns were considerably slower and less variable than in the early 80's.