Hated to give you the wrong idea, if you're familiar with my other postings you would know I'm as against illegal immigration as any of you. It's just the obsessive nature of the author's writing that rubbed me the wrong way. I have my doubts that events in those regions have transpired the way they have for the reasons he espouses. The illegals follow the industries that hire them. But banishing illegals and keeping out "low-income" people and anti-development mania get conflated in the author's mind and I think he mixes it all together and puts a nasty gloss on it. It's the PC local governments and their "sanctuary" laws that allow the enemy to concentrate.
I live in Northern California and I can tell you that his analysis of the difference in what happened between Northern and Southern California is quite accurate. It is still happening: in Santa Cruz county, the citizens just voted down a measure to widen Highway 1, which would help mitigate the massive jams we have now.
Why? Because they rightly perceive that improving the infrastructure will only invite more people to move here, regardless of race or nationality, and the problem will only return. So they figure that they'll live with the current catastrophe, and not give it a chance to get worse.
I disagree: I think if the immigration laws had been enforced, we could widen our roads without having to worry that another million Mexicans will appear overnight to set up camp. It's their way of having their cake and eating it too: they don't overtly condemn Mexican illegal immigration, they just erect unseen barriers like lack of infrastructure, zoning density laws, housing permit requirements which are impossible to meet, etc. which drive up prices and make it difficult for unskilled laborers to move in. Sidenote: it won't work in the long run, because eventually, ethnic agitators and other Democrats will agitate for required low income housing in developments (as just happened in Sacramento County), or outright "public" housing projects to house the illegals (which is already the case in majority Mexican parts of Santa Cruz and Monterey County, i.e., Watsonville and Salinas).
He's simply pointing out that that in Los Angeles, it didn't happen that way. LA simply kept building out, with illegals congregating in the urban core and whites (and blacks, interestingly enough) simply moving to the periphery or out of state alltogether. And the theory is that LA did not have the same "no-growth" attitude, and what it looks like now is the result of that. It may not be the only reason (industries willing to hire unskilled, illegal alien workers being another, as you point out), but it certainly is one of the reasons, and a big one at that.