Hi, I think without a dealer in San Francisco with a physical address then you need to optimise the page on your site for the dealer you have in Santa Rosa complete with citations for their location (Name, Address, Phone number).
The success of the Santa Rosa dealer's page for searches for San Francisco will largely depend on the competitiveness of other dealers listed on the Internet that are selling the same products with local citations closer to San Francisco. If there are limited dealers to be found for San Francisco then Google will spread it's net wider to find other relevant results. That said, your Google+ Local listing showing coverage should help your site page.
I hope that helps,
Peter