The mountain community of Big Bear, California is a southern California skiing destination.
To check out the conditions I Googled Big Bear and read the following...
A request from the Big Bear community to POSTPONE any visits until COVID 19 is behind us.
A reminder that having strangers come there will jeopardize the people living there whose home it is.
There is no law yet that forbids it. You can go and ski and do your thing totally ignoring the polite request of the folks who live there.
How selfish are you? What is true of Big Bear is true of all skiing destinations for the people who live there. Invading their home to pleasure yourself for a few hours? Seriously. You would do that?