This just in from the rental company:
From 101 North go to Petaluma. Take the East Washington Street Exit. Turn left after crossing over the freeway. Continue on East Washington Street, which will become Washington, Bodega, Valley Ford Road, and eventually Highway 1. Continue through Bodega Bay and north for several miles. When you see a brown sign for Goat Rock State Beach, you are almost there. Just past Goat Rock Road, in amongst large cypress trees, we are the first driveway on the left. There is a chain link gate and a street sign that reads Circle Drive. The mailbox says 9555. If you pass over a bridge into the town of Jenner, you have gone too far.
Alternate route (marked with a big X in the packet of information we received, but this is how we got there . . . )
From 101 North go through Santa Rosa. Take the River Road exit. Turn left, continue on River Road--it will merge with 116--continue until you reach Highway 1 (one mile before Jenner). Turn left on Highway 1, crossing the Bridgehaven Bridge. You will see a brown sign for Goat Rock State Beach 1/4 mile. We are the first driveway on your right, the driveway is amongst large cypress trees. There is a chain link gate and a street sign that reads Circle Drive. The mailbox says 9555. If you get to Goat Rock Road you've gone too far.
Total driving time is 1.5 to 2 hours from San Francisco or the East Bay.
map is here