I think part of the California Coronavirus problem is caused by Arizona

The above map displays the problem California is facing from Arizona.  If you look at the map of cases in Arizona you can see because of the proximity and business and travel between Arizona and California that the coronavirus rate in California would naturally be affected by business and travel between Arizona and California.

I was surprised when Arizona joined Texas and Florida as three of the highest coronavirus case loads in the entire country.

It's likely we need to start quarantining Arizona visitors for 14 days to mitigate the problem but because of the way western states operate which is different than eastern states that is unlikely to happen.