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Early on 18 April 1906 a section of the San Andreas fault roughly 290 miles long ruptured, shaking San Francisco and a long stretch of northern California. Fractured water mains left firefighters with little water, and fires burned for about three days. Army-led dynamiting to create firebreaks, often done by inexperienced crews, is described as having started new fires as well as stopping some, and much of the gold-rush city was destroyed.
The San Andreas is a transform fault where the Pacific plate moves northwest past the North American plate, with no crust created or destroyed. Because the plates lock together along the fault, strain builds up over decades and is released in sudden slips.
Chinese residents could then claim they had been born in the city, and so were citizens, without documents that could disprove it. Citizenship let them sponsor 'paper sons' from China, which gave a way around the Chinese Exclusion Act.
Many insurance policies covered fire but not earthquake damage. City leaders also wanted to reassure investors that San Francisco was safe to rebuild. Winchester shows that describing the disaster as 'the Great Fire' helped with both aims, so the name people used for the disaster decided who paid for it and how its risk was seen.