How do you explain the surge in Covid cases in California?

I thought I was going to get an answer when I saw the headline:

‘We are getting crushed.’ What’s behind the alarming rise in California’s Covid-19 cases

This headline appeared on CNN.com. Eagerly I devoured the story. Unfortunately the story talks about the problem without offering any new insights. In fact, other than a thinly disguised barb at Republican house districts, the story added not one iota to my knowledge:

“The Covid-19 numbers statewide do not reflect a scenario where more conservative parts of California are failing while liberal parts are thriving, albeit according to state figures some of the hardest struck counties per capita reside in Republican US House districts.”

I thought, given the fact that California is as blue as it gets, and Democrats know all about Covid, we would have tracking and we would know where each case comes from. Unfortunately, other than stats I have seen on the Fox channel that less than 2% of cases originate in restaurants, I know nothing else.

Does anybody know?