Studies show that most homeless are "locals," but some percentage do travel to more desirable areas, plus some towns and other institutions will just give a homeless person a one way ticket to get rid of them.
However, I'm skeptical of the usefulness and accuracy of the official data we have on the homeless.
Homeless lives are lived largely in secret. They may have no address and no phone.
This is a vulnerable population and the system does not serve them well. I imagine even a lot of self-reported data is unreliable because vulnerable people will lie at times to protect themselves.
In the US, a lot of homeless data is based on the annual Point In Time count which occurs in late January. I recently tripped across an article that explicitly stated it occurs at that time because it's the coldest part of the year and homeless individuals do their best to seek shelter, if only temporarily.
So it seems to me that this count is likely an undercount and it's an undercount entirely on purpose.
I participated in planning meetings for the local Point in Time Count last year. I've also seen anonymous questions online from people participating who had concerns about various populations being overlooked by the count, such as post-hurricane victims still living in hotels after their house was destroyed.
I traveled to the West Coast while homeless. I intentionally returned to California because the West Coast is better for my health. I then spent about 5.5 years homeless in California before leaving the state to get back into housing someplace cheaper.
California is exporting poor people to other states and has been for years. If you are a waitress or trucker or similar, you will be better off elsewhere.
But homeless people can end up stuck in place in California. The weather in large parts of California make it fairly tolerable to sleep outside. This can become a recipe for long term homelessness.
Data does suggest that California has more homeless who are unsheltered and more chronic, long term homelessness than most places. Off the top of my head, I think California has 8% of the US population and an estimated 25% of our homeless.
So either California is incredibly broken or it's a de facto dumping ground for the nation's homeless. I suspect there's some truth to both interpretations.
Re drugs:
I think generally think drug abuse is usually a symptom of other problems. I'm not someone who believes in the Twelve Step model of addiction. Research and first-hand experience with users suggests that's not an accurate model.
The history of Alcoholics Anonymous is that it began with a few hardcore alcoholics whose alcoholism was literally killing them and they still could not stop, so they gave it up to God and that worked. Now, every college student who goes on a bender is at risk of being called an alcoholic and sent to AA. Reality: Older people typically drink less than younger people with absolutely no outside intervention whatsoever.
Given that general mental framework, I see our national drug crisis as a statement that there is something very wrong with our overall social fabric. If you fix that, then the drug crisis will die down.
It will never go away entirely. There will always be people trying to drown some of their sorrows for one reason or another. But the levels we are seeing speaks to something rotten at the heart of our society.
Generally speaking, I think we need single payer national healthcare and we need to fix our housing supply issues. Those two things would go a long way towards restoring a healthy social fabric to the US.