If you are just looking to see Redwoods, no need to go North of San Francisco into Marin at all. There are a bunch of Parks and open-space preserves that are *also* South of the Airport. Wunderlich Park in San Mateo county has redwood groves, as does Purisima Creek and El Corte Midera open space preserves....if you are willing to do a little walking. Now if you really want to see *lots* of Redwoods with minimal walking, go down to Big Basin Redwoods State Park (southwest of San Jose).