The unexpected earthquake caused most of the deaths — somewhere between 3,000 and 5,000 people. Firestorms fed by fierce winds raged for three days in San Francisco and caused the majority of the damage. The terrified inhabitants could walk away from a fire, as they did dragging trunks and holding bird cages, but only the most agile and quick thinking could escape an earthquake.
The water system's distribution pipes in the city broke, leaving little water with which to fight the many fires that flared up within the first hour. Horse-drawn fire engines sped from one hydrant to another, but frustrated firemen found very little water to pour on the fast-spreading flames. Underground cisterns were tapped for what little water they contained, and a few hoses were coupled together and sucked water from the bay. The hot, dry desert winds blowing from the northeast fanned the flames, whose great heat — exceeding 2,000 degrees — was enough to combust the interiors of steel-framed buildings. There was nothing to do but use the only tool that was available, and that was explosives. The extensive dynamiting only spread the flames.
Meanwhile, nearby Army troops — soon to be augmented by marines, sailors, the state militia, student cadets from the University of California, and self-proclaimed vigilante groups — took over law enforcement without martial law ever having been declared. The armed troops were issued orders by the mayor to "KILL" anyone suspected of committing a crime. An undetermined number of people were shot, adding to the death toll.
Refugees fled west to the untouched Western Addition and Golden Gate Park, east by ferry to Oakland, or south to San Mateo. The Southern Pacific Railroad gave free passage to those who wanted to flee further. An area of 4.7 square miles or 508 city blocks was blackened during those three days. There were also fires in Ft. Bragg, San Jose, and Santa Rosa. The writer Jack London, who was in both cities, believed that Santa Rosa "got it worse" than San Francisco. Regardless of which city suffered most, the earthquake and fires combined to cause the nations' greatest urban tragedy.