On a May 2007 visit to San Francisco, I found time to do some biking in the Golden Gate National Recreational Area, also known as the Marin Headlands.

Good maps of the area are available for downloading here: http://www.nps.gov/goga/planyourvisit/maps.htm

I rented a bike from Bay City Bikes near Fishermans Wharf and road across the Golden Gate bridge into the headlands. I can recommend Bay City Bikes; the staff was helpful and the premium bikes were trail-worthy.

I rode Conzelmen Road to the top of Hawk Hill (920 feet). From Fisherman's Wharf to the top of Hawk hill took about 2 hours with a stiff headwind and multiple stops for the seemingly unaviodable photos of the Golden Gate bridge. The road is all asphalt so the riding, although tiring, is not difficult.

Next, I ventured off-road. Taking a turn off Conzelmen Road onto Bunker Road where I saw a Bobcat run along the shoulder and duck into the undergrowth. Next I picked up Miwok Trail which went uphill for about one mile. The ascent is not a switchback but more of a continuous incline. As I rounded one curve, I surprised a 4 foot Rattlesnake that was out sunning on the trail. I gave a shake and found cover in the grass on the uphill side of the trail. I was unable to get a good photo, but you can see a bit of it's side in one photo.