The most beautiful coastline that you will ever see is from Bodega Bay, CA North. I would highly recommend that you head west from Napa to Petaluma and then over to the coast at Bodega Bay. The Pacific Coast Highway ( 1 ) hugs the coast with lots of curves and mountains but it is easily passible. I would recommend taking it all of the way to Rockport where it bends back East and connects to 101 to finish your trip North. I would also recommend an overnight stop in Ft Bragg to give you time for a little exploring - Mendocino has great restaurants and shops and the Skunk Train through the redwoods in Ft Bragg is well worth the time.