Every morning a great wall of fog descends upon the city of San Francisco. It begins far out at sea. It forms over the Farallons, covering the sea lions on their rocks, and then it sweeps onto Ocean Beach, filling the long green bowl of Golden Gate Park. The fog obscures the early morning joggers and the lone practitioners of tai chi. It mists up the windows of the Glass Pavilion. It creeps over the entire city, over the monuments and movie theaters, over the Panhandle dope dens and the flophouses in the Tenderloin. The fog covers the pastel Victorian mansions in Pacific Heights and shrouds the rainbow-colored houses in the Haight. It walks up and down the twisting streets of Chinatown; it boards the cable cars, making their clanging bells sound like buoys; it climbs to the top of Coit Tower until you can't see it anymore; it moves in on the Mission, where the mariachi players are still asleep; and it bothers the tourists. The fog of San Francisco, that cold, identity-cleansing mist that rolls over the city every day, explains better than anything else why that city is what it is.