it seems reasonable that the federal government can invoke extraordinary powers for a limited amount of time to address federal-sized and -scoped problems. in this case, that seems to be the Public Health Service Act (PHSA) which, among other things, allows for quarantines in times of health crisis.
the states have police power via the 10th amendment, which reserves all powers not delegated to the fed to the states (didn't know about dillon's rule until now, although that was my general understanding of where power lies, in states not municipalities). and it sounds like a narrowly-interpreted privileges or immunities clause of the 14th amendment further allows states to use police power as long as it doesn't infringe due process or equal protection.
one question is how much the feds can compel state actions in this regard (seems like not much, but feds can use their own forces if need be), and another is how much states can act independent of the feds (seems like feds can delegate the response to states)?
can states simply compel lockdowns by police power, other than hoping no one notices and sues? apparently Jacobson v. Massachusetts (1905) allows for compulsory vaccinations by states for general health and welfare.
regardless of the legal basis, to me, it's pretty clear that our governments (especially CA) poorly and blindly targeting its efforts for maximal political (and media) gain rather than for health and safety.
if it had been for the latter, the first highly visible thing we'd have done was immediately quarantined senior care facilities, super-PPE'ed all their workers, paying whatever it took to create a tight bubble around each facility, to protect seniors. that would have targeted 60+% of potential mortalities (and yes, we knew that was a core threat back in february). then we could address other specific threats and beefed up medical facilities as needed. and lastly, we'd have singularly messaged the heightened dangers of social gatherings and the effectiveness of distancing, along with an educational campaign on the mechanism of spread, co-morbidities, the age stratification of risk, and such, not masks and its complicity-signalling value.
then residents could make informed choices on how to protect themselves. some would choose to isolate, but many would just distance where necessary and avoid large gathering of strangers. we then wouldn't need to worry so much about legal precedent, and we wouldn't be dividing into stupid political camps lobbing vicious tweets (and sometimes more) at each other.