https://www.siliconvalley.com/2021/08/02/covid-qa-what-you-need-to-know-about-the-new-bay-area-mask-order/

Less than two months after COVID-19 public health orders were lifted across the state, the Bay Area has announced a new mandate requiring residents to cover their faces in public indoor spaces.

Those orders — prompted by an alarming spike in cases thanks to the fast-spreading delta variant —  will go into effect Tuesday in San Francisco, Santa Clara, San Mateo, Alameda, Contra Costa and Marin counties.