DeadheadSF

So I'm getting back into road cycling after over a decade of not riding much at all. Part of getting back into riding shape is racking up some miles on (mostly) flat rides. I'm far from ready for hills at this point, but most of the routes I've seen posted on various sites all involve some degree of climbing. Can anyone recommend some flat routes/loops that are 25-30 miles or longer? If the routes manage to avoid streets with heavy traffic, that'd be a big plus.

I've done a bit of googling already, but like I said, everybody always wants the hills, it seems.

Thanks