To give an idea of affected counties, these are from lists on the FEMA site for eligible assistance. For full details refer to FEMA.gov, this list is not an authoritative list of who is currently officially eligible for assistance.
Individual assistance:
Alameda (County)
Amador (County)
Calaveras (County)
Contra Costa (County)
Mendocino (County)
Merced (County)
Monterey (County)
Sacramento (County)
San Joaquin (County)
San Luis Obispo (County)
San Mateo (County)
Santa Barbara (County)
Santa Cruz (County)
Ventura (County)
Public assistance:
Alameda (County)
Alpine (County)
Amador (County)
Butte (County)
Calaveras (County)
Colusa (County)
Contra Costa (County)
Del Norte (County)
El Dorado (County)
Fresno (County)
Glenn (County)
Humboldt (County)
Inyo (County)
Los Angeles (County)
Madera (County)
Marin (County)
Mariposa (County)
Mendocino (County)
Merced (County)
Monterey (County)
Napa (County)
Nevada (County)
Placer (County)
Sacramento (County)
San Benito (County)
San Diego (County)
San Francisco (County)
San Joaquin (County)
San Luis Obispo (County)
San Mateo (County)
Santa Barbara (County)
Santa Clara (County)
Santa Cruz (County)
Siskiyou (County)
Solano (County)
Sonoma (County)
Stanislaus (County)
Sutter (County)
Tehama (County)
Trinity (County)
Tulare (County)
Tuolumne (County)
Ventura (County)
Yolo (County)