At 5:12 a.m., the San Andreas Fault ruptured along nearly 300 miles, sending violent shaking through San Francisco. Gas lines burst and ruptured water mains left firefighters helpless as flames consumed over 28,000 buildings. The disaster displaced half the city's population of 400,000 and reshaped American ideas about urban fire codes and seismic engineering.
Witnesses described the ground moving in visible waves, church bells ringing themselves from the shaking alone, and chimneys toppling through roofs in the first violent seconds. But it was the fire, not the quake, that truly destroyed the city. With water mains shattered, firefighters resorted to dynamiting buildings to create firebreaks, sometimes starting new fires in the process.
The blaze burned for three days, consuming 500 city blocks and leaving refugees camping in Golden Gate Park as ash rained down. Official death tolls of around 700 were deliberately understated by city boosters anxious to protect San Francisco's reputation for investors; modern historians estimate the true toll near 3,000.
The catastrophe transformed American engineering. Cities nationwide rewrote building codes, and the study of the San Andreas Fault that followed helped found modern seismology in the United States.