My wife is Chinese-American, born and raised in San Francisco. Her family presence here dates back to the 1890s. Chinatown in SF is not a new thing, been there from the beginnings around 1850, and following generations spread throughout the SF Bay Area. So your "virtually all" comment is not true.
It’s a matter of numbers.
The Chinese population at the time of the Exclusion Act was about 105000 I believe. The total population in 1880 was 865000-ish. So at the time of the cutoff, they were 12% of the population, heavily concentrated in Northern California.
But that population was lopsidedly male if you recall. They were contract laborers who ended up looking for work after the UP was finished and the mines played out. So “natural growth” was truncated, and exacerbated by the cutoff.
By 1920 the total population of California was 3.4 million and the total Chinese population could not be much larger even with the “paper sons” scam. So by 1920 they were ~ 3% of the population. And that didn’t change materially until 1965, even with the 1943 Act, since the 1924 Act ratcheted down non-Western European even more.
So my statement stands. With ~ 12 million Chinese now in the United States, the VAST majority have come in the last 50 years.
And using your favorite site, let’s look at Cupertino in the year 1970:
http://www.bayareacensus.ca.gov/cities/Cupertino70.htm
Note that there are (drumroll please) exactly 189 people of the Chinese race (self identified, of course) in that town, compared to 17552 white people, comprising 1% of the population for the Chinese and 96.4% for the Caucasians.
Kinda lopsided, you know?
Note the 1990 census shows the whites at 29913 and the Chinese at 5310, for a gain of 2700%, and the whites gaining by about 70%, although it was a decline from the 1980 census.
So uh...the Chinese in the South Bay were a tiny minority just 20 years earlier. As for SF, I remember Chinatown in the 60s. It was far smaller, and still was the biggest concentration in the area. I do remember all the hipsters in SF complaining about the expansion of Chinatown in the 1980s, which I thought was hilarious coming from people who styled themselves as cosmopolitan “world citizens”.
But it just proves my point. The post-’65 act immigration is by far the largest cohort of Chinese people in the United States. There were people who were here for generations - mainly in the SF and LA Chinatowns. But that was a small minority. I was not unaware of that when I made the statement, and factored it in. The numbers are not unfamiliar to me.
The Asian population of Cupertino was 36895 at the 2010 Census and does not break down Chinese vs anyone else. So it has to include South Asians, i.e., Indians. That total is now 63% of the population. Caucasians have declined (again) to 18270, and you can bet that the 2020 Census will show that even more.
So we can’t quickly compute the ratio of 1970 Chinese to 2010 Chinese in Cupertino, but it would undoubtedly be a huge number.
But once again, as of the current date, comparing to the numbers in 1880...or even 1920...or even 1970...the VAST majority have come in the last 50 years, and most in the last 40.
BTW, now that Asians outnumber Caucasians 2:1 in Cupertino as an example, can you tell me which part of China experienced a similar “demographic shift” that turned the existing population into a minority in the same time span? And what you think they might have done in the face of such a thing?