2 SSPX centers in Northern California (Sacramento and Los Gatos) are both in cities. Granted, the chapel in Sacramento (actually Carmichael - but same difference) is not in the center of the city but in a more suburban residential area.
I would think that the retreat center in Los Gatos is in the city as well, since there is not much rural area in that part of the state.
The FSSP has a very stable and large parish in Sacramento as well. It is located in a the middle of a poor, immigrant section of the city and is situated right in a black and mexican ghetto neighborhood. The FSSP also has a very beautiful mission style church in the Los Angeles area.
The Institue of Christ the King has a very small chapel in Santa Clara (which is near Los Gatos) - right in a business section of the town.
I do not know of any sedevacantist chapels in Northern California, although I think I may have heard of one in the Bay Area?