For example, San Francisco: http://hsh.sfgov.org/research-reports/san-francisco-homeless...
Los Angeles: https://www.lahsa.org/documents?id=2059-2018-greater-los-ang...
According to the 2017 SF survey, 10% of homeless were out of state when they most recently became homeless. According to the 2018 LA survey, 14% were out of state.
I am not sure if you should entirely trust these numbers, or if they are asking exactly the right question---everyone involved knows that there's a right answer and a wrong answer to the question---but it's the best we have.
And according to a UCLA study, "65% of unsheltered homeless individuals have lived in the county for more than 20 years." That means 35% have been here less than 20 years.
http://www.latimes.com/business/la-fi-ucla-anderson-forecast...
And how many of the homeless were born in the county? I suspect it's a very low considering so many residents in the county of L.A. aren't native born.
There's a funny advertisement for the Grinch movie here in L.A. which rings true. The line says, something like, "My favorite time of year is Christmas, when everyone goes back to where they came from."
I think a much more likely explanation than "California just churns out crazy people at a phenomenal rate" is "There's probably a connection between the insane housing prices and the crazy high levels of homelessness there."
Also referring to the geek wire article, low income doesn’t necessarily mean homeless, especially chronically homeless. CA just tends to help them move to low income housing in cheaper parts of the state