We took Journey On to Petaluma in 2016, two years ago. The Petaluma River was fine and fun/interesting with plenty of depth/width. We also found out that a 25' C-Dory can go under the Petaluma Bridge at low tyde if you put the antenna down. And, as shown on the charts, there's a mud bank on the starboard side, which shows at low tyde. Stay in the middle of the river as you approach the bridge then bear to port until you tie up at the docks. The marina at the Petaluma River entrance appears to be gone.
Jim Gibson with the Delta and Bay Extravaganza should have the latest information.
Petaluma certainly is a more interesting place to visit than Napa. The dock are next to a great bunch of restaurants, the old Carnegie Library is a great place to visit and they have a town walking tour. And don't forget American Graffiti was made there. First place my dad worked after he came to the US and we have a son living nearby so it's visited frequently (by auto.). Don't miss it.
Boris