We could tell you that San Francisco has exhilirating mountain biking and you would not believe it. It is not a popularly held opinion that San Francisco is a "fat tire friendly" zone. Ask a SF mountain biker about all of the nice local rides, and you'll typically get, "San Francisco? Well, you can take a nice ride at Skegg's Point or in Marin Headlands."
Skegg's Point, officially known as El Corte de Madera Open Space, is a nice ride, no doubt, but it is a 40 minute drive from SF. To get to the Marin Headlands, which are exceptionally fun to ride with many miles of fire roads (sorry, singletrack closed to bicycles), you have to either add 10 miles to your round trip ride distance or deal with the traffic and parking problems associated with the Golden Gate Bridge. (You can also take the 28 or 29 MUNI to the Golden Gate Bridge, with all buses equipped with front bike racks. MUNI map here.)

Luckily San Francisco proper DOES have nice mountain biking: dirt roads, singletrack, forest groves, peak climbs, ocean views, historic places and great places along the way to eat, grab a coffee or stay the night. The trails for biking are in some places clearly defined and in others they are open for interpretation. A surprising amount of available San Francisco riding is not on pavement, 50% or higher for some of the loop rides. There are vital, though probably unplanned and relatively overlooked, pieces of connecting trails or "greenways" which provide for off-pavement mountain biking between various parks within the city to create satisfying trail loops. San Francisco mountain biking will treat you to roots, curbs, jumps, rocky descents, technical maneuvers and plenty of opportunities to do some "cloud splitting", if you only know where to go. It is the urban freeride.

All this combines to create the "San Francisco Linked-Loop Shared-Use Off-Road Trail Network"

Upon exploration, it has been found that several distinct and complete trail system loops exist within San Francisco. There's the Presidio Loop , passing through the green hills of the Presidio, the rocky paths of Land's End/Lincoln Park with dramatic ocean views. There are 2 Golden Gate Park Loops, which have more than 10 miles of singletrack and narrow dirt trails!. There's the Ocean Beach/Harding Park Loop with its views of the Pacific Ocean, Fort Funston, Lake Merced and endless sunset riding opportunities. There's the Twin Peaks Loop, a trail along the highest point in the city at 850' with an optional jaunt to the top of Mt. Davidson and its massive hilltop cross. There's the Buena Vista Park/Corona Heights/Mt. Sutro Loop, running just behind the Haight and the UCSF Medical Center. See the San Francisco Mountain Biking Map for a top level view and links to these ride descriptions.

As an added bonus, the conditions of San Francisco make it possible to enjoy extended mountain bike treks and multi-day excursions without sacrificing your comfort or your enjoyable biking experience. Additional trails connect San Francisco to Pacifica, the Marin Headlands and beyond!! All of this makes for a huge trail network available to the local or the visitor. Even if you aren't a tourist, it's always nice to make a mountain biking day trip to visit the ocean or eat at a restaurant. Local businesses probably won't mind if mountain biking and mountain bike tourism bring more customers their way.

San Francisco .... it's not just for cars anymore!