https://www.siliconvalley.com/2020/10/21/coronavirus-state-tracker-heres-every-county-tier-assignment-as-of-oct-20/ > San Francisco County was the only additional one of California’s 58 counties moved on Tuesday, Oct. 20, to the least restrictive, yellow tier of the state’s coronavirus tracking system. > Counties are assigned to a tier based on metrics showing the speed and the spread of the virus in their borders, and each Tuesday the state updates their status.