[Magellan, in its corporate wisdom, will not supply updated maps for the GPS model I own.]
The BEST way to get from Route 4 to the Brannan Island KOA is to turn right at the light on Route 12 and take a right on Jackson Slough Road, then turn left on Brannan Island Road. It is NOT, repeat NOT, advisable to turn right off Route 4 onto Brannan Island Road directly, despite GPS instructions to do so! Even the USPS agrees.
As the road got more and more narrow and twisty along the top of the levee, I didn't really start to get uneasy until the sign that said One Lane Road Ahead. The road we were on was about 6 inches wider than the RV on each side but still qualified as a Two Lane Road (I guess) because there was a yellow stripe down the middle. Just as I was trying to find a wider spot in the road to turn around, we spotted a US Mail truck headed our way along the levee. The driver drove his truck down along the side of the slope -- really! -- to pass but I flagged him down. "Is there really a KOA up ahead somewhere?" I asked. "Yes ma'am, about 3 more miles. But ... no one ... ever ... takes ... THIS road ..."
I was in dire need of a drink by the time we arrived and set up camp.
Coming home, after delivering daughter and grandsons to son-in-law at the Berkeley Marina, it should be a straight shot home, no? No. GPS routed me onto a (very scenic) frontage road along the bay for a while before allowing me back onto I-580. And, the maps are old; they date from BEFORE the I-980 cut! GPS tried to take me onto Routes 13 and 24 to get to I-880. Sigh.
This GPS, my dear Mary Magellena, is going to have to find a new home with a younger family member; preferably one with a greater desire, tolerance, and appreciation for adventure.