I was going to respond by saying that the American Graffiti type atmosphere continued to exist along Van Nuys Boulevard up until the mid 1980s, at least the middle class apple pie America part of it. I think that might be stretching it a bit. It probably did last up until about 1980, but like you say, that is splitting hairs.
I was stationed at Camp Pendleton the first time in early 1982. I wasn't back again until late 1998. I couldn't believe the difference in just those 16(ish) years. Basing my judgment on purely anecdotal evidence, I'd estimate that the Hispanic population at least tripled.