There is no one cause. Anyone who says there is, is wrong.

CA has many problems. Houses are expensive, and that makes it impossible for poor people to buy a house. This is something that CA can fix over time, and those who are only homeless because they cannot afford a place to live are low hanging fruit. They only need to build a lot of housing (reforming zoning for example)

There are also people who are homeless because of some other problem. Mental issues, drug addiction, and other such things. they are harder to deal with - I'm not sure what can be done about it: I've seen a lot of proposals, but people proposing them tend to be overly optimistic about the ability of their ideas to work without downsides.

There are more issues as well, but those are the big ones, and you cannot treat them the same.