There is strong evidence COVID-19 was not circulating in the Bay Area in January. Samples collected by the Seattle Flu Study in Jan/Feb 2020 have been retested and COVID-19 was not found before Feb 21. As Trevor Bedford says, had COVID-19 been circulating in CA it almost certainly would have showed up quickly in WA. There is other evidence based on the genetics of sequenced viruses. Details: https://twitter.com/trvrb/status/1249414291297464321