Until today I knew less about Petaluma than Snoopy. But it seems it really exists, in California north of San Francisco. The Petaluma River flows south through a delta into the wide and shallow San Pablo Bay, which opens into San Francisco Bay (thank you, Wikipedia!).
The Sacramento Chapter of the Traditional Small Craft Association rowed the Petaluma River recently for an open house at a new Heritage Centre run by the Friends of the Petaluma River.
David 'Thorne' Luckhardt (who took the shot above) posted pictures of the event here, and Rick Thompson (whose picture below captures someone having a lot of fun) has more here.