Filming has started for the upcoming Reese Witherspoon and Mark Ruffalo romantic comedy "If Only It Were True," based on an adaptation of local novelist Marc Levy's 2000 novel of the same name. If you don't recognize the location, it's 16th and Valencia - photoblogger Bill of Mermaniac tells us the bookstore location has been renamed is "Abandoned Planet". It seems there's already been a sighting of Ms. Witherspoon at Dolores Park over the weekend.

The crew will be filming in the city through the 23rd. Nancy Hayes is casting the local extras, although casting seems to be complete for now. We wonder where Reese and Mark will be staying -- picket lines better not be crossed or we'll call our friends in the film unions! SFist figures it will be the Clift, but the production could also have rented a house or two for the paparazzi-shy stars. Needless to say, principal photography for this story based in San Francisco will be filmed on sets in Los Angeles. The San Francisco Film Commission is expected to announce that local schlock jock Chris Columbus will be shooting the full production of Rent -- starring one of SFist's favorite Hollywood hotties, Rosario Dawson. The announcement should come in the next week, and bodes well for future big-budget shoots by the Bay.

Photo by Bill of Mermaniac.