From the PD, here:

Appointments will be required at the new test sites — Santa Rosa High School and the Petaluma campus of Santa Rosa Junior College. OptumServe, a nationwide health services company, is running all such sites in the state.

Residents can go to https://lhi.care/covidtesting or call 1-888-634-1123 to schedule an appointment. No drive-up testing will be offered.