Yeah, illegal immigration and anchor babies are a big part of this, but don’t forget legal immigration. We admit over a millions legal immigrants per year, hundreds of thousands of which are Hispanic, and many of those go to California. I believe California is also the top destination for Asian immigrants as well, and they have favored the Democrats as well since at least Clinton. If we ended all illegal immigration, then California would still be on its way to becoming a Mexcian state, and would still be increasingly out of reach for the GOP.
It may be true that later generations of immigrants turn more Republican, but that is a false hope to cling to now. For one thing, all past waves of immigration were followed by periods of very little to moderate immigration. This wave shows now sign of ending on its own (and it won’t due to extended family chain migration), and the GOP establishment has not got behind any serious effort to reduce immigration. In fact, some Republicans helped torpedo the last attempt that had a real chance of success during the Clinton administration.
They never end on their own. One ended in the early 20th century when the quotas were dropped to around 100,00 - 200,000 per year and stayed there until 1965.
This huge legal immigration really started under GHWB when the quotas were raised to 780,000 (or 870,000), and have since been raised to 1.2 million or more. Of course, the quotas moved up gradually from 1965 to GHWB.
This big influx of immigrants will only end when Congress and the president lower the quotas for legal immigrants, and give no amnesty to illegals.
According to Allan Hoffenblum, party registration among among Asian voters in California last year was 30% Democratic, 29% Republican. Among White voters, it was 42% Republican, 40% Democratic.