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Residents and visitors in over half of California’s 58 counties should put back on masks when they’re spending time indoors, according to the Centers for Disease Control and Prevention.

That’s because the counties, which are concentrated mostly in Northern California, have a “high” COVID-19 community level — a metric the CDC evaluates every seven days.

It’s based on three different factors: New hospital admissions per 100,000 people, the percent of staffed inpatient beds occupied by COVID-19 patients and total new cases per 100,000 people.

Here are the 38 California counties where health officials recommend wearing your mask indoors again:

This map shows the CDC’s COVID-19 Community Levels for counties across the state as of June 30, 2022. In red regions, deemed “high,” residents and visitors should wear masks indoors again, the agency says. (Photo: CDC)
  • Alameda County
  • Amador County
  • Calaveras County
  • Contra Costa County
  • El Dorado County
  • Fresno County
  • Kern County
  • Kings County
  • Lake County
  • Lassen County
  • Madera County
  • Marin County
  • Mariposa County
  • Mendocino County
  • Merced County
  • Monterey County
  • Napa County
  • Nevada County
  • Placer County
  • Plumas County
  • Sacramento County
  • San Benito County
  • San Francisco County
  • San Joaquin County
  • San Mateo County
  • Santa Clara County
  • Shasta County
  • Siskiyou County
  • Solano County
  • Sonoma County
  • Stanislaus County
  • Sutter County
  • Trinity County
  • Tulare County
  • Tuolumne County
  • Ventura County
  • Yolo County
  • Yuba County

Notably, California’s most populous counties did not make the list.

San Diego, Los Angeles, Orange and Riverside counties were all listed as “medium” level. San Diego had been deemed “low” in the set of numbers released June 23, but bumped up a notch in Thursday’s data.

San Francisco County — home to one of the state’s largest cities — was listed in the “high” category.

The CDC reminds all Californians to get vaccinated and boosted, and to get a coronavirus test if they have symptoms. Health officials add that “people may choose to mask at any time” regardless of community level, and that anyone “with symptoms, a positive test, or exposure to someone with COVID-19 should wear a mask.”

In areas with high COVID-19 levels, the CDC says anyone at risk for severe illness should consider taking additional precautions besides simply wearing a mask. That includes staying 6 feet away from others, avoiding crowds and poorly ventilated spaces, and washing their hands often.

You can view complete state- and county-level data on the CDC’s website.