I couldn't find THE biggest tourist attraction, but there are a few sites, like the one below, that list the top ten things to do in SanFran.
Link: http://gocalifornia.about.com/cs/sanfrancisco/a/sfbest.htm
because it is a good tourist attraction
Qualcomm Stadium is a tourist attraction in San Diego, California. It is the home of the San Diego Chargers.
Lombard Street! It is the most crooked street in America. Or the Golden Gate Bridge
San Pedro Island is one tourist attraction in region VIII. Biri Rock formations are another tourist attraction in the area.
"Fisherman's Wharf is an extremely popular tourist attraction in San Francisco, California. Here you are bound to find great restaurants and hotels, as well as historical landmarks."
It is in user because it is now a tourist attraction.
3D Tourist - 2011 3D Tourist San Francisco Part 1 1-1 was released on: USA: 10 June 2011
3D Tourist - 2011 3D Tourist San Francisco Part 2 1-5 was released on: USA: 24 June 2011
westfield
In recorded history it was the 1906 quake.
The Palace of Fine Arts is located in the San Francisco Bay Area. It was originally built to exhibit works of art at the 1915 Panama-Pacific Exposition and is now a popular tourist attraction.
Lombard Street in San Francisco, California, is known as the "crookedest street in the world." This iconic street features eight sharp hairpin turns on a steep incline, making it a popular tourist attraction.