The following is an excerpt from [0].
Around the same time, the Court ruled, in O’Connor v. Donaldson, that a Florida man named Kenneth Donaldson had been kept against his will in a state psychiatric hospital for nearly fifteen years. The ruling added momentum to a nationwide campaign to “deinstitutionalize” the mentally ill. Activists decried the existence of mental hospitals that were filled, as one account put it, with “naked humans herded like cattle.” During the next two decades, states across the country shut down such facilities, both to save money and to appease advocates pushing for reform. But instead of funding more humane modes of treatment—such as community mental-health centers that could help patients live independently—many states left the mentally ill to their own devices. Often, highly unstable people ended up on the streets, abusing drugs and committing crimes, which led them into the prison system.
[0] http://www.newyorker.com/magazine/2016/05/02/the-torturing-o...
Specifically in California, among them are:
* weather that's survivable without permanent shelter
* other states in the American West bussing their homeless to the state
* CA Governor (and later US President) Reagan's abdication of the role of the government in aiding the chronically ill (especially mentally ill) and/or homeless.